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Had there been a non-flying pterosaur?
Since there are non-flying birds and secondary non-flying insects, it is reasonable to assume there were also non-flying pterosaurs.

Well, according to this source there are no flightless bats, so it isn't an absolute that all flying clades have flightless members:
https://pterosaurheresies.wordpress.com/2011/07/21/meet-the-first-flightless-pterosaur-sos-2428/

Everyone knows about the various flightless birds: the penguin, the dodo, the ostrich… the list goes on. There are no flightless bats. And no one has ever discovered a flightless pterosaur… until now.

But the short answer to your question is: no confirmed flightless pterosaur fossil seems to have been discovered so far.
The longer answer is: from what I can tell no pterosaur has been found that was clearly flightless, but pterosaur flight isn't well-understood in the first place so there is debate as to how and whether some specimens could have flown. It seems to be the consensus so far that they did fly however (based on the lack of mention of flightlessness on the Wikipedia page, and the last paper I link to in this answer is fairly convincing).
As far as not finding flightless specimen, the above link claims to have found one but the source is not reputable and I found no confirmation of it elsewhere (Wikipedia confirms, and I'm usually all about Wikipedia but here the page has all the hallmarks of having been written by the same person who wrote the blog). The same author argues a large pterosaur is flightless here, but their arguments are quite poor compared to others made in the field and they seem again to be the only ones making them.
Here is a post from Tetrapod Zoology in 2008 imagining what a flightless pterosaur might be like, and also claiming none have been found:

Long-time readers will know that I am an unashamed fan of both speculative zoology, and of Dougal Dixon’s hypothetical ‘alternative’ animals. Inspired by a comment made here in August by Jenny Islander, I have been having a re-think about the possible evolution of flightless pterosaurs: the fossil record gives no indication that such animals ever existed, and maybe they didn’t, but that hasn’t stopped people from speculating.

A similar quote from the 2004 book "Posture, Locomotion, and Paleoecology of Pterosaurs":

So far, there is no example of flightless pterosaurs.

The Wikipedia page for pterosaurs makes it clear how hard it is to figure out how pterosaurs flew.
Here is one of the main arguments that the largest pterosaur Quetzalcoatlus northropi was flightless

The estimated mass for the largest pterosaur known, Quetzalcoatlus northropi, exceeds the previous highest estimates by more than 100%, and it is argued that this extremely large pterosaur is better interpreted as a secondarily flightless form.

And an argument that the largest pterosaurs would have been flightless based on a comparison to modern oceangoing birds:

Our result therefore casts doubt on the flying ability of large, extinct pterosaurs. The largest extant soarer, the wandering albatross, weighs about 12 kg, which might be a pragmatic limit to maintain a safety margin for sustainable flight and to survive in a variable environment.

This paper summarizes the debates and argues against those assessments (the whole paper is worth reading actually):

While the conclusions on giant pterosaur flight by Chatterjee and Templin [19], Sato et al. [17], Henderson [25] and other workers using avian analogues for pterosaurs are not without merit, we find that they leave themselves open to criticism by not considering alternative data sources when making inferences about the palaeobiology of extinct animals. Giant pterosaur anatomy, functional morphology and, in the case of Pteranodon at least, sedimentary context all indicate that they were flighted animals and, likewise, clear anatomical distinctions between birds and pterosaurs indicate that only basic mechanical details can be treated interchangeably.

+1 for skepticism about the pterosaur heresies, which is "wrong in just about every detail ... It’s just bad science"

Two more flightless pterosaurs have been discovered.
Alcione is a flightless nycotosaur.
http://reptileevolution.com/nyctosaurusUNSM.htm
PIN 2585/4 a flightless unnamed anurognathid
http://reptileevolution.com/jeholopterus-CAG.htm

Can you provide peer-reviewed evidence here for flightlessness here, rather than just links to your own webpage.

Sorry, but no. A ms. describing one were rejected because I had not seen the specimen recently, after I had seen it a year earlier. That bogus rejection was only one of the reasons why I decided to start the web page. All the data is there for anyone to judge the validity of the reconstructions.


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Solute potential of sucrose relative to NaCl
Does 1M NaCl or 1M sucrose solution have a more negative solute potential?
I was thinking that for the same volume of solution, (eg 1 dm^3) there will be 2 mol of ions in NaCl solution and 1 mol of sucrose.
However, there are more OH groups in sucrose that water can form hydration shells around.
So which solution has the more negative solute potential?

I would say 1 M NaCl has lower solute potential. By the equation, solute potential is proportional to solute concentration.

Yes, but how do we account for the fact that sucrose has more OH groups that water can form hydration shells around? Wouldn't that lower the solute potential to a greater extent than NaCl? There are more OH groups per mole of sucrose than there are ions per mole of NaCl.

You are right. NaCl has a van't Hoff factor of 2. For simplicity you can assume sucrose as a simple solute and ignore macromolecular interactions. BTW, even sodium and chloride ions will have a hydration shell and its size depends on the surface charge density.

So, we assume that the hydration shells formed around Na+ and Cl- ions are bigger than those formed around sucrose (which we assume to have only one hydration shell formed around it)?

Hydration shell is a totally different concept. I don't think it is a major factor in osmolarity. Osmolarity is a bulk property.

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What is the function of epidermal ridges on human fingers (that produce fingerprints)?
What function is served by the epidermal or capillary ridges on human fingers, the supposedly unique impressions of which are known as fingerprints?

In this case, it seems that @canadianer successfully identified some positive selection-based answers. But, honestly Mark, I would read my neutralist answer too... too often people "expect" a selection-based answer, when most of the time the answer is simply neutral.

So that I can my phone's fingerprint sensor! Just kidding. ;-)

It's not just humans that have fingerprints, they're also present in many of our closest relatives and have separately evolved in Koalas and North American Fishers.

It should be noted that fingerprints may not be considered as a reliable unique identifier as they once were. http://www.naturalnews.com/044876_fingerprints_law_enforcement_forensic_science.html And also that some farmers and some old people can have rubbed out fingerprints.

I find it ridiculous that so many questions like this ask "what is the evolutionary reason…". You could ask whether "whatever is the technical term to describe the feature of the skin that you are referring to" (and it is not fingerprint — do a little work before posting) has any function. But to assume that every feature of an organism is selected for is an intellectual blind alley.

@StephanBranczyk: Natural news dot com is not a trustworthy source. Google "quackwatch naturalnews".

Fingerprints no longer uniquely identify people. http://www.nbcnews.com/id/5053007/ns/us_news-security/t/fbi-apologizes-lawyer-held-madrid-bombings/#.WMngMW_yu70 You could say fingerprints suffer from hash collisions (computer science and cryptography).

I like the new title, it focusses on the general trait rather than a specific patterning of some finger, X

I found many plausible claims that fingerprints increase friction. However, the following article claims, at least under their experimental conditions, that fingerprints actually decrease friction with smooth surfaces by reducing contact area.
Fingerprints are unlikely to increase the friction of primate fingerpads.

It is generally assumed that fingerprints improve the grip of primates, but the efficiency of their ridging will depend on the type of frictional behaviour the skin exhibits. Ridges would be effective at increasing friction for hard materials, but in a rubbery material they would reduce friction because they would reduce contact area. In this study we investigated the frictional performance of human fingertips on dry acrylic glass using a modified universal mechanical testing machine, measuring friction at a range of normal loads while also measuring the contact area. Tests were carried out on different fingers, fingers at different angles and against different widths of acrylic sheet to separate the effects of normal force and contact area. The results showed that fingertips behaved more like rubbers than hard solids; their coefficients of friction fell at higher normal forces and friction was higher when fingers were held flatter against wider sheets and hence when contact area was greater. The shear stress was greater at higher pressures, suggesting the presence of a biofilm between the skin and the surface. Fingerprints reduced contact area by a factor of one-third compared with flat skin, however, which would have reduced the friction; this casts severe doubt on their supposed frictional function.

That said, the author does later discuss their potential role in gripping of rough or wet surfaces:

So why do we have fingerprints? One possibility is that they increase friction on rougher surfaces compared with flat skin, because the ridges project into the depressions of such surfaces and provide a higher contact area. Experiments on materials of contrasting known roughness are needed to test this possibility.
A second possibility is that they facilitate runoff of water like the tread of a car tyre or grooves in the feet of tree frogs (Federle et al., 2006), so that they improve grip on wet surfaces. Though there is evidence that friction falls on fingers coated with high levels of moisture (Andre et al., 2008) it is possible that it falls less quickly on fingertips than on flatter skin. Once more, suitable experiments could test this idea.

There seems to be more consensus on the idea that fingerprints are useful for tactile sensation. The following are just some articles which discuss this.
Effect of fingerprints orientation on skin vibrations during tactile exploration of textured surfaces.

In humans, the tactile perception of fine textures is mediated by skin vibrations when scanning the surface with the fingertip. These vibrations are encoded by specific mechanoreceptors, Pacinian corpuscules (PCs), located about 2 mm below the skin surface. In a recent article, we performed experiments using a biomimetic sensor which suggest that fingerprints (epidermal ridges) may play an important role in shaping the subcutaneous stress vibrations in a way which facilitates their processing by the PC channel. Here we further test this hypothesis by directly recording the modulations of the fingerpad/substrate friction force induced by scanning an actual fingertip across a textured surface. When the fingerprints are oriented perpendicular to the scanning direction, the spectrum of these modulations shows a pronounced maximum around the frequency v/λ, where v is the scanning velocity and λ the fingerprints period. This simple biomechanical result confirms the relevance of our previous finding for human touch.

The role of fingerprints in the coding of tactile information probed with a biomimetic sensor.

In humans, the tactile perception of fine textures (spatial scale <200 micrometers) is mediated by skin vibrations generated as the finger scans the surface. To establish the relationship between texture characteristics and subcutaneous vibrations, a biomimetic tactile sensor has been designed whose dimensions match those of the fingertip. When the sensor surface is patterned with parallel ridges mimicking the fingerprints, the spectrum of vibrations elicited by randomly textured substrates is dominated by one frequency set by the ratio of the scanning speed to the interridge distance. For human touch, this frequency falls within the optimal range of sensitivity of Pacinian afferents, which mediate the coding of fine textures. Thus, fingerprints may perform spectral selection and amplification of tactile information that facilitate its processing by specific mechanoreceptors.

This paper also asserts a reason for the elliptical nature of fingerprints:

In humans, fingerprints are organized in elliptical twirls so that each region of the fingertip (and thus each PC) can be ascribed with an optimal scanning orientation.

The first paper shows that fingerprints decrease friction when gripping dry acrylic glass, but I guess there wasn't much dry acrylic glass in the environments where fingerprints evolved. It might be quite different when gripping rough or wet surfaces. (But for all I know there might be plenty of research on that as well.)

@Nathaniel Much in the same way that slick tyres are better than anything on dry tarmac, but you'd want treads on rough or wet terrain.

Would this mean that people without fingerprints could be measured to have less sense of touch than those with?

@Nathaniel I agree. As I said, their experiment is not exhaustive, but literature on this subject seems hard to come by (at least in my admittedly brief search).

Clarity on the TLA: PC, in "and thus each PC", please.

Just a gentle push and you're in 10k club! Congrats ;)

Extensive amount of research, I've learnt a lot from this. Particularly on the final quote TQ

To balance the debate, from a neutralist evolutionary perspective...
There does NOT have to be a direct selective pressure for a trait's contribution to an organism's expressed phenotype.

Three alternative, neutral, explanations:

"Hitch-hiker" traits: It (the trait) could be a by-product of a more necessary component whose function is directly associated with survival. E.g. we have hair, and it happens to have a colour, the colours perceived in the specific pigmentation of our hair are not strongly selected, one way (blonde) or the other (brunette), at least as significantly as the functionally essential properties of the hair itself: to keep our ancestors nice and warm. This brings us to...
Ancestrally Inherited Vestigial traits: once evolved, they can take a long evolutionary time "to get rid of". This accounts for traits we still express phenotypically, yet whose original functional purpose is obsolete today. For example, the Coccyx and our defunct visual sensor, a more optimal design is found in squid eyes: the retina should be ahead of the vitreous gap to avoid blind spots, a "glitch" only we measly mammals have to deal with. At least we have a good brain, right? Those pesky, extinction-imminent, tigers have nothing on us. And as for those echidna, still laying eggs? That's soo last-epoch...
Neutral Evolutionary Regimes: mutations whose inheritance patterns are heavily driven by a force known as genetic drift (wiki). Long story...

Side Note
A most remarkable trait, in my opinion, is found in the blind cave fish. Why does this fish have eyes, when it can't see?
Have a guess: which of the answers listed above is true: 1., 2. or 3.?

Related topics:

Is there a name for the evolutionary loss of vestigial structures?

EDIT/s:

2017-03-17: Correction (kudos AliceD): I mixed up reasoning about the mammalian eye example, floaters was not the suboptimal trait, it was blind spots. No blind spot in cephalopod eyes.

In response to your cavefish question, without guessing ;) http://biology.stackexchange.com/questions/34466/is-there-a-name-for-the-evolutionary-loss-of-vestigial-structures/34471#34471

I think in this case, neutral evolution is highly unlikely, because of the convergent evolution of fingerprints in other species (e.g. Koala and North American Fisher) which appears to be linked to their lifestyle and habitat but it's still important to consider other explanations.

@JackAidley You still need to make sure there's no other trait that is linked to fingerprints that's the actual result of convergent evolution, with fingerprints being just a common side-effect of that.

@JackAidley, I would argue that you're missing a key facet about fingerprints: their large variability in, at least, Human populations... You need to be sure what you mean by "finger print", a specific patterning? Because if maximum friction was the evolutionary "end game", surely we'd all have gecko hands?

@JeffreyBosboom, feel entirely free to edit that in the bottom of the answer following the "---" markdown symbol. Search: "Pending correction of mammalian eye example."

Mammalian retina location is a very bad example. It does serve it's purpose so it's promoted. The fact that better solutions exist is meaningless to the evolution process. Switching to a better solution would require un-evolving vision first - that just aint gonna happen. Same with vas deferens being looped over the pubic bone, pointless but "we've invested too much in this solution to scrap it now".

@Agent_L. touché. I agree to you on some level, but "meaningless", is a bit harsh right? What I meant, is what I agree with you on, essence being: Natural Selection is a "blind watchmaker" -- Dawkins. See: https://en.wikipedia.org/wiki/The_Blind_Watchmaker. Care to edit my answer?

Why wouldn't a squid eye have floaters? You could mention the absence of a blind spot in squid eyes

@AliceD: touché, EDITED. I mixed up my optimal design reasoning in mammalian vs. cephalopod eyes.

Glad I could help. +1

@hello_there_andy No, I believe "meaningless" is the right word here. Evolution literally doesn't care that objectively better solution exists somewhere (unless another species can outcompete you thanks to that solution). I don't think there is a reason to evoke Dawkins either, he's needed when someone can't grasp the basic concept of evolution and people participating in this discussion seem to have no problem with that.

@hello_there_andy There is no "grand blind watchmaker concept" to realize, the very basic idea of evolution is that grand concept. Blind watchmaker is just a way to explain it, an "evolution for dummies" story. We are not dummies here, please don't treat us so. Dawkins is controversial figure even among evolution proponents, because he's dangerously close to preaching science like just another religion. And I don't agree evolution is a bad watchmaker, it's a very good one. Because it's better to release a successful product that works than spend too much resources on unneeded improvements.

Nothing to add but: "Let's see if your cavefish still has eyes in a million years! :) ) PS: There's a newly discovered cave loach. It's awesome.

@Kara more importantly, let's see if we if we can adapt to a hotter climate, low oxygen levels, and competition with an expected H.sapiens population size of 12 Billion by 2039!

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Anatomy of seeds (dicot and monocot)
Do all dicot seeds have endosperm? Will they be retain as they grow and what are the difference with its monocot counterpart?

You are asking a broad question. Can you please add relevant details to narrow down your question so that it is answerable in a few paragraphs (at max).

Will dicots always have endosperm?

no all dicots seeds don't retain endosperm, e.g.: Fabaceae


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For which taxonomic levels are xylotomical, embryological, and palynological evidence each most useful in determining species relationships?
From the 2010 USABO Semi:

In plant systematics, three
  lines of evidence may be useful in determining relationships; xylotomical (wood anatomy),
  embryological and palynological. Match these three with the level for which they are most
  useful.

The options for the levels were order, family, and genus. The answers matched xylotomy to genus, embryology to order and family, and palynological to genus, but if anybody could provide some examples to explain that would be great. Thanks!

Do you have any initial ideas yourself about the given answers, as a starting point?


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How can I measure bee and wasp population?
Bees and wasps in our garden disappeared suddenly last year - I asked a question about it at Why our bees might have suddenly disappeared. This year, I see that some bumblebees are active now. I'd like to measure the population of bees and wasps in the garden over the year, and see if the numbers change when the nearby fields are sprayed.
I note the question How best to count bees entering and leaving a hive to measure hive activity? but I don't have a hive to count. Our bees come from far away, and I'm interested in multiple species from multiple nests, and wasps too. So I'd need to count the number visiting the garden. But, can I count reliably? It will vary with weather, and the number on any one plant will vary greatly depending on plant flowering dates.
Is there any established protocol for counting bees and wasps in the wild to look for population changes over time?
I can't spend too much time on this - I might manage an hour every week. Or, I could set up camera recording, if someone knows some really clever software to do the counting. But I still can't imagine how to overcome the variation.
Thanks!

 Short Answer
No. You cannot appropriately examine population dynamics using the approach you've described.
You can, however, examine how foraging frequencies vary/correlate with field spraying (though this might take more effort than you're looking for).
 Long Answer
You're not going to be able to properly quantify population levels from casual observance.

Because you would be unable to effectively identify individuals, you would be unable to know if you're seeing different individuals or repeats of previous individuals.
The data are also biased toward those species or individuals that use the habitat features in your particular garden and are biased against those that do not (Parsons & Szewczak, 2009).
Further, you would have no way to identify which hives/nests that individuals are coming from (without watching them leave the nest directly), so you would not know which populations are represented at any given sighting.

Unfortunately, although the question you link to (How best to count bees entering and leaving a hive to measure hive activity?) would allow you to better examine/compare separate populations, those methods likewise suffer from the same shortcomings listed above.

What you can figure out:
Your causal observance can at best be used to quantify foraging frequency in your garden.

In other words, you would just be able to count how many bees visit your garden at any given time and compare those values at different discrete time points. You could compare this to a number of environmental variables to look for trends.

In your case, your approach would look something like the following:

You could count the number of sightings (or landings or feedings) in various random locations throughout your garden.

Each of these locations should be randomly selected, and you would preferably collect numerous random samples from each of various "habitats" (i.e., different locations, different flowers, etc.).
You must return to the same locations each time and spend the same amount of time at each location each sampling period.

You can do simple statistics on these different samples across all sampling periods to examine foraging frequency trends across time.
If you directly measure a number environmental variables (e.g., temp., precipitation, humidity, cloudiness, etc.) you'll be able to rule out variance in your data due to these factors.

Proper background research would be required to determine which variables might be important to measure.

Finally, you could do regression/ANOVA analyses to examine any correlation between nearby field spraying on your foraging activity.

However, there are a ton of variables that could affect the trends you see, so final analyses will likely be weak at best.

Measuring those aforementioned environmental variables will help with this, as will increasing your sampling rate. See Power Analysis

Power analysis is an important aspect of experimental design. It allows us to determine the sample size required to detect an effect of a given size with a given degree of confidence. Conversely, it allows us to determine the probability of detecting an effect of a given size with a given level of confidence, under sample size constraints. If the probability is unacceptably low, we would be wise to alter or abandon the experiment.

Note: Work by J.E. Eckert (1933) showed that (honey)bees can travel multiple miles from their hive/nest, so unless those fields are mutliple miles away, any pesticides could very well impact the populations visiting your garden.

Another Option:
You could perform Trap Counts to try to approach quantifying populations rather than just quantifying foraging behavior.

This method is used frequently for other insects. However, I found very few reputable sources examining bees/wasps.

One example: Danka & Gary (1987) estimated foraging populations effectively, but they did so by collecting data at the hive entrance.

Though there is an inherent issue with trap studies as well:

As Petrovskii et al (2012) point out:

Traps are effective at providing relative counts that enable comparisons but are poor at delivering information on the absolute population size.

However, Petrovskii et al (2012) show that a ‘mean-field’ diffusion model is capable of revealing the generic relationship between trap catches and population density.

Their paper is freely available here.

Citations

Danka, R. G., & Gary, N. E. (1987). Estimating foraging populations of honey bees (Hymenoptera: Apidae) from individual colonies. Journal of economic entomology  80(2): 544-547.
Eckert, J. E. (1933). The flight range of the honeybee. Journal of Agricultural Research 47:257-285.
Parsons, Stuart and Joseph M. Szewczak (2009). Detecting, Recording, and Analyzing the Vocalizations of Bats In: Ecological and Behavioral Methods for the Study of Bats. Thomas H. Kunz and Stuart Parsons, ed. The Johns Hopkins University Press, Maryland, 2nd ed., pp. 91-111.
Petrovskii, Sergei, Daniel Bearup, Danish Ali Ahmed, Rod Blackshaw (2012). Estimating insect population density from trap counts. Ecological Complexity 10: 69-82. http://dx.doi.org/10.1016/j.ecocom.2011.10.002.

Wow! I need to do some reading! Thanks for all this, let me get back to you.


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Sex and human's sexual urge.
Why is it necessary for humans to feel pleasure while having sex? Why is it that other animals don't need to experience it? Is it evolutionary ? Why do we mate for pleasure when it's so energy wasting/ time consuming?

How do you know other animals don't like sex?

@user137 I know animals like to have sex as well but they do it only for reproduction and not for pleasure. Only certain species do it for pleasure. I know this kinda sound taboo but I'm curious about this

How do you reconcile your two assertions "animals like to have sex" and "they do it ... not for pleasure"? Seems contradictory to me. How well do you think, say, a dog understands its own reproductive biology? Is the dog thinking "I must propagate my species" while copulating?

http://biology.stackexchange.com/users/29114/solanacea I mean that's their instincts to reproduce

@TheoneandonlygreatK Wouldn't enjoyment of something be a great way for an evolutionary process to "enforce" an instinct? What other options are there? Withdrawal/relief from a negative stimulus can also be somewhat pleasurable/enjoyable: i.e., drinking or eating when you are thirsty/hungry.

Plenty of animals have sex for pleasure, dolphins and porcupine are known masturbators. your assumptions are just wrong.

This is logical question and somehow related to evolution.
See mating is pleasurable to most of animals
Second thing during course of evolution mating became pleasurable not because humans can take pleasure but to attract them towards mating therby increasing population of a species helping it to survive.

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Well Plate Method VS Kirby Bauer Method
Any pros and cons? One puts the test substance in sterile discs, while the other one puts it directly into wholes in the agar. Any thoughts?

I came across a nice Master's thesis that investigated precisely that. The conclusion reads as follows:

Automated microbroth dilution-based testing methods are increasingly used by many
  clinical microbiology laboratories to determinate antimicrobial susceptibility. Thus, it is vital that
  these methods are able to accurately determine the correct antibiotic susceptibility patterns of
  microorganisms being tested. In our laboratory, we use the Trek Sensititre system (Well Plate Method). However, if
  this system cannot accurately detect resistance visualized as inner colonies on the Kirby Bauer
  Assay, then the clinical importance of the Trek Sensititre may be called into question.
Our study showed that the Trek Sensititre was unable to detect the
  additional resistance of inner colonies that are detected using the
  Kirby Bauer Assay. Nevertheless, there are a number of important
  limitations associated with the study: Firstly, the inner colonies
  used in the study were pooled from all inner colonies from the Kirby
  Bauer plate. Because the colonies were pooled, in some cases from
  different antibiotic zones, it is possible that a mixed population of
  resistant organisms that were selected for by the different
  antibiotics were tested. This possible mixture of multiple different
  subpopulations may make the results difficult to interpret. Secondly,
  some inner colonies were selected from antibiotics that do not have
  any CLSI- 47 approved interpretations and would be considered
  inappropriate to report. For example, some Pseudomonas aeruginosa
  isolates displayed inner colonies to ertapenem, an antibiotic that has
  no CLSI interpretations and a drug that would not be used clinically.
  The Trek Sensititre results from those inner colonies showed
  additional issues with multiple different antibiotics. Clinically, the
  patient would not have been treated with that antibiotic, so that this
  resistant set of subpopulations may not have been selected for. Thus
  the results from the study may not be clinically significant but it
  does open up questions to the possibility that the Trek Sensititre may
  not detect clinically significant resistant subpopulations.
Given that
  the Trek Sensititre can miss resistant subpopulations in Gram negative
  bacilli, it is important to establish the clinical relevance of this
  finding. If the inner colonies selected for by each of the antibiotic
  discs was sub-cultured individually instead of pooled together and
  then run on the Trek Sensititre, then the following results may
  possibly differ from the pooled inner colonies. An important future
  direction would be to determine whether the unreported resistance from
  the organisms in the study had an effect on patient care however, this
  was beyond the scope of this thesis study. Thus, the clinical
  significance of this study’s findings require future study.
  Nevertheless, laboratories should be aware of the potential for
  missing sub-populations of antimicrobial resistant organisms using
  broth-based microdilution methods.


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Is there something that makes flies slower at high altitudes?
At first glance, higher altitudes equal lower temperatures, which would likely slow down cellular metabolism.  However, while backpacking in New Mexico in ~90 degree weather, I experienced the same thing -- the flies were slow enough I was able to catch them easily in my hand, as well as with chopsticks.
Is this related to air density?  Why are these flies so much slower to react and move about in the mountains.

The atmospheric density may not be the only factor, but from a physics standpoint, flying animals should in general move more slowly at high altitude.
As an example, New Mexico's Wheeler Peak is at an altitude of ~4 km above sea level. For a back-of-the-envelope air density calculation, a good estimate of scale height is 10 km, i.e. $\rho(h) = \rho_{sea}*e^{-h/10km}$ , which means the air density at Wheeler Peak is about $2/3$ the density at sea level (other air conditions being equal).
For wing-flapping animals, the power required to maintain flight is inversely proportional to the air density. I'm not confident about how flies' wing movements would be affected (this is where an entomologist should step in), but in any case their air speed should be reduced at high altitude.

It may be influenced by inter-species differentiation in characteristics.  Were the flies larger or smaller than other flies?  If there were flies of different sizes present in the same location and under the same temperatures, how did their relative speeds compare?
To know the species of fly which one is examining is quite difficult.  It can come down to counting hairs on the fly's body under a microscope--literally.  But some species may simply have different habits when compared to another species.
Mosquitoes are in the same order as flies (Diptera), and in Southeast Asia there are many species of mosquitoes.  Some make a noise or hum while flying; some fly silently.  Some are quite fast; others are much slower to take off, making them easier to slap.  Some have an uncanny ability to sneak in and bite while one is otherwise occupied/absorbed in something, while others seem too eager and land in plain sight while one is watching.  Some are larger, with more painful bites; others are smaller and their bites itch longer after their deed has been done.
A consideration of these simple variables leads to the obvious conclusion that more information about the flies in question might be needed before a determination could be made as to why they seem slower.
Air densities might be a factor, in addition to gravitational forces.  I'm not knowledgeable about the relative impact of thinner air versus the amount of gravity to be overcome in flight, but I know large jet airplanes fly faster and with less drag (resistance) at higher altitudes, making high-altitude flight more efficient.

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Looking for a database of plant features
To perform some private data science experiments I am looking for accessible information on morphological plant features (tabular information would be best). Crawling the web I found many websites with limited more general description and a lot of information on location and population data.
Do you know a website, institute or person in possession of such data and willing to share it? Since I am located in Germany my main interest is in the local flora, but any other would also do the job.

-- Traits --
TRY
TRY is a Plant Trait Database. More formally, it's a network of vegetation scientists headed by DIVERSITAS/IGBP, and the Max Planck Institute for Biogeochemistry, providing a global archive of curated plant traits.
BioTraits
This is an online resource for empirical data on how biological traits respond to environmental drivers such as temperature, light, and salinity.
Nate Swenson
Nate and his collaborators have compiled a ton of traits for species all over the world (though focused on the tropics).
Coyle et al. 2014
Appendix 2 of their 2014 Ecography paper lists primary literature sources and publicly available trait databases they used to examine 3 traits: leaf nitrogen, seed mass, and wood density.
-- Images --
Morphbank
An international Web database that contains thousands of high-resolution photographs and other images of plant and animal specimens.
Botanical Images Databases
This site provides dozens of links to databases containing plant images. There are also regional databases provided (e.g., Pflanzenphotos.de).
Botany.ch
This site contains both text sources (e.g., lectures and essays) as well as links to morphology picture databases (e.g., Botanical Image Database of the University of Basel).

See also FAO Online Catalogues for a number of morphological sources in both English and German.

There is the TRY database of plant traits:
https://www.try-db.org/TryWeb/Home.php


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What type of subsoil root structure provides better plant anchorage?
Which type of root is better for good anchorage for small plants: tap roots or fibrous roots?. How about for trees:  tap root or a fibrous system?

This is partially dependent on soil texture/types


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For how long can influenza survive on a piece of paper?
Consider the following hypothetical: A graduate student would like to return a set of assignments before a certain deadline, but she currently has the flu and may sneeze or cough while grading the papers at home. Under the assumption that she has just graded the papers but is still in possession of them, how long should she wait before returning them to the students? At what point does the risk of transmitting the flu to a student via paper become negligible?

Unlikely. Because as long as she has the flu (and we're talking about the real influenza here, not just some nasty cold) she will neither grade any papers nor return them because she will be in bed being sick.

Perhaps just eight to 12 hours.

Both influenza A and B viruses survived for 24-48 hr on hard, nonporous surfaces such as stainless steel and plastic but survived for less than 8-12 hr on cloth, paper, and tissues. Measurable quantities of influenza A virus were transferred from stainless steel surfaces to hands for 24 hr and from tissues to hands for up to 15 min.

--Survival of influenza viruses on environmental surfaces.
Or, perhaps, up to 17 days, when in the presence of "respiratory mucus" (i.e. snot), although even then a couple days was more plausible. Note that this was on Swiss banknotes, which isn't standard paper.

Influenza A viruses tested by cell culture survived up to 3 days when they were inoculated at high concentrations. The same inoculum in the presence of respiratory mucus showed a striking increase in survival time (up to 17 days)....  When nasopharyngeal secretions of naturally infected children were used, influenza virus survived for at least 48 h in one-third of the cases.

-- Survival of influenza virus on banknotes.


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Transfering Odds Ratios to another SNP with high LD?
I have the Odds Ratios (OR) for a particular risk allele in a SNP (I'll call it SNP1).  That SNP was unfortunately not genotyped in my data, but I don't want to throw it away.  I have looked up the SNP on LDLink and another SNP (I'll call it SNP2) is in high linkage disequilibrium with SNP1 (R2=0.94).
How do I transfer the OR from the SNP1 allele to the corresponding SNP2 allele?
I know it is something similar to log(OR)*sqrt(R2) but I'm not entirely sure.  Could somone please clarify if this is the correct formula?


text:
Example of code with pypgen (python)
I have a VCF file and wish to calculate a few indices of population divergence over a sliding window.
I consider using pypgen but the documentation is currently very limited. Can you please give me an example (for Jost'D for example) of a code that would work?

vcftools can compute a few things in sliding windows (Tajima's D, Pi, Fst, LD at least), but that's probably not enough, is it?

Nope it is not indeed. It cannot calculate Jost's D or Dxy for example. There is also EggLib (for which I am currently reading the documentation).


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In Vitro Meat Initial Production
I've gotten interested in the science behind in vitro meat, and I was wondering what would be necessary to create it. Would you initially need a primary culture, or an immortalized cell line? And how would you go about creating such a culture that differentiates properly?
The closest analog to this, I think, would be tissue regeneration but I'm finding it hard to figure out the answers to these questions.
Thanks so much!


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Western blot transfer issues
I am having some issues with transfer efficiency to nitrocellulose membranes. To get all the technical info out of the way:
Transfer method: Wet, tank transfer overnight at 30V with normal tris-glycine transfer buffer + 20% methanol. I do this at RT with stirring. Of note: I have not recently been equilibrating my gel in transfer buffer, as this was reported to decrease transfer of basic proteins due to the stripping of SDS (I can furnish this reference if anyone is interested).
Sample: In all cases these are in vitro reconstituted nucleosomes with or without certain enzymes--the main transfer issues are the core histones, which are highly basic (pI 10-11). There should be no more than about 100 ng of each histone being transferred per lane. The salt in the sample is <25 mM. They are boiled prior to loading. There is no noticeable precipitate in the samples before or after boiling, however the volume is quite small (20 ul) so I would not necessarily detect precipitation.
Nitrocellulose is 0.2 um and is pre-equilibrated in transfer buffer prior to transfer.
The gel: I use a 15% gel, 1.0-1.5 mm thick. The acrylamide I use is 37.5:1 acrylamide:bis. Some issues could arise here--the acrylamide solution is about 1 year old and has been stored at RT that entire time (which is what is recommended on the label). In addition, we typically keep a stock of 10% APS at 4C, so I cannot guarantee my APS has not gone bad.
I have been quite careful generally to ensure there are no bubbles between any components of the sandwich and filter paper/foam pads are soaked in transfer buffer.
Now to the issue. Attached are images of the membrane after transfer (and also after processing, thus the relatively high background from the blocking buffer) as well as the gel after transfer. As you can see from lane to lane I seem to have differing transfer efficiencies. This has occurred with my last three blots. My first thought was sample precipitation, but I have not had this issue before despite running essentially the same blot many many times over the past year.
Any thoughts? Quite frustrating, as it has appeared suddenly with identical protocols/reagents as before.

I've never done it, but I remember hearing that histones are very hard to work with in SDS-PAGE and Westerns because of their basic nature -- conventional gels and blots assume that the proteins are acidic because of the SDS bound to them, but that isn't true with histones. I see one protocol for histones here.

The first thing that comes to mind for me is that the transfer seems excessive... isn't histone sub-20 kDa? I have often transferred similar-sized proteins at 4C for 30 min, 30V.
In general, presence of SDS will inhibit transfer efficiency, and increasing alcohol in your TG buffer will counteract the effect of SDS present. Perhaps bring down the methanol to 10%? I would be curious to see that reference regarding the SDS/pre-equilibration, though. That certainly runs contrary to how I understand it working. (Note: I flip-flop between equilibrating or not equilibrated my gels without any observable differences.)
If your acrylamide or ACS had gone bad, your gel wouldn't set.
If you don't already, I'd suggest running a Bradford or BCA on your samples to be sure that you're loading the same amount into each well. Having loaded more into each well could give the appearance of uneven transfer.
To be honest, I don't really see what you mean by uneven transfer, based off the Coomassie and Ponceau. If you're seeing a gradient effect across a large portion of the gel, I would suggest you visually inspect to make sure that the gels you cast are even width all the way across. Having a thicker gel in one place than in another could impact the resistance (heat) in that part of the gel and impact transfer. If you're seeing a lane-by-lane transfer efficiency shift, I would suggest localized pH or temperature changes due to uneven loading of salts, protein concentration, or lipid concentration.
Hope this helps!


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Are hormone secretion variations the same for a pair of monozygotic twins?
I have recently read a paper about how stress affects morning salivary cortisol levels in an individual. I am conducting a study on monozygotic twins and was wondering if cortisol levels would fluctuate similarly in a pair of twins, or whether cortisol and other hormones are unrelated to the genetic makeup of the twins.

Bartels et al. 2003 is a review that reports an estimate of the heritability of the cortisol level of 0.62. In comparison to most traits, it is a relatively high heritability.
So, in short, the answer is "no". Cortisol level variation is lower among twins than among unrelated individuals. If the definition of heritability is a little bit unclear to you, you should have a look at this post.
The reaction norm of cortisol level (and other stress response) with varying stress level also seems to be heritable (Ilsing and Hoelsboer 2006, Volckaert et al. 2012).

"So, no cortisol level variation is lower among twins than among unrelated individuals"... I believe you're missing a comma after the no, am I right?

Yes indeed! A comma changes everything! Thanks

No worries, already upvoted anyway!


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Using Chi-squared analysis to confirm expected phenotypic ratios of offspring
In a recent question the original poster was faced with deciding which ratios to use in a Chi-squared analysis. They were supposed to decide on, "logically", what test-ratio to use.
Example question:
A supplied sample contains four types of seeds and the total number is 64. The
types of seeds are large red 42, large white 8, small red 10 and small white 4. Calculate goodness of fit.
My initial assumption was that in order to solve the problem, you would need to think about the genotype of each parent.
Lets say:
L = large seeds;
s = small seeds;
R = red seeds;
w = white seeds
If both parents were LsRw, the phenotype-distribution of the offspring would follow a 9:3:3:1 ratio.
If one parent was LsRw, and one parent was ssww, you would have a 1:1:1:1 ratio.
And if one parent was LsRw, and the other parent was Lsww or ssRw, you would have a 2:2:1:1 ratio.
Obviously, out of all of these ratios, the example question follows most closely with the 9:3:3:1 ratio.
So, to solve this question statistically, would you make the null hypothesis There is no difference between the observed and expected ratios?
While the alternative hypothesis would be There is a different between the observation and the expected ratios?
And would a statistically significant result indicate that the null hypothesis must be rejected in favour of the alternative hypothesis, thus the parents are unlikely to be heterozygotic for both traits?

I suspect that the actual question contained more information than what was posted. If not, presumably you could formulate a null and alternate hypothesis for each expected ratio to determine the phenotypes of the parents, though as I type this I can't help but think there would be some statistical reason not to do it this way. Perhaps you would get a better answer at Cross Validated.

You're correct, each time you run a statistical model you are introducing an error of ~5% to your conclusion - that would be the reason to not do it that way. But this question has had me thinking for a couple days so I thought I'd see if anyone has any other approaches to the problem with the limited information available. If indeed it is a matter of just thinking about inheritance, I'm not sure if the statisticians would be able to catch on.

For any statistical test the definition of the null hypothesis is essential. You cannot guess the null hypothesis based on a given question. The null hypothesis is based on some prior knowledge. There is no way to guess it. Moreover, what the alternative hypothesis is does not really matter because the statistical test does not say which one of the infinite possible alternatives is correct. The test just accepts or rejects the null hypothesis and for any test the first step is to define the null hypothesis; everything else is after that. Plus, a test cannot be performed with just one sample!

In the example you considered, the null hypothesis is basically that observed value is not different from an expected value for which the prerequisite is the knowledge of the expected value. Now what the expected value is, depends on your model. You assumed one possible inheritance model and proceeded towards calculation. However, this assumption has to be clearly stated and understood by the experimenter before performing the test. OP's professor did not talk about any underlying model and simply asked to check goodness of fit. It is ridiculous; I can assume anything as per my convenience.


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Why Japanese cherry trees blossom so early in spring?
My understanding is that flowers' main benefit are the insects which attracted to the shape/taste of these and facilitate cross pollination. Yet the Japanese cherry trees start (and end) to blossom (in my observation) way before the most of insects become active. What is the evolutionary explanation for such a behavior?

Might be good to read Austen and Weis 2015

Perhaps your assumption about insect activity is wrong?  We're just now getting early spring flowers (crocus, snowdrops, &c), and bees (or something bee-like) are busy pollinating them.

Well in Tokyo now it's just above 10C during the days, and it's half of that in the nights. Yet the local 梅 (ume) trees already have bloomed and now are naked again - the leafs will appear in another 3 weeks I guess. I don't think I could spot any insects so far.


text:
Can there be medium height(neither tall nor short) pea plants in Mendel's experiment?
Can there be medium height(neither tall nor short) pea plants in Mendel's experiment?
All textbooks I have read seem to imply that pea plants have to be either tall or short, nothing in between.

Medium height (like in people) and other traits that seem like a mixture of two extremes are often a result of incomplete dominance. For example, a red and white flower are bred to produce an offspring with pink petals.
Mendelian genetics does not include incomplete dominance (which is classified as, surprisingly, non-Mendelian genetics).
Basically, Mendel got very lucky with his choice of plant. Pea plant height is strictly dominant, meaning one dominant allele results in tall plants, regardless of the identity of the second inherited allele. This is a consequence of the genetic makeup of pea plants. Had he tried a similar experiment with snapdragon flower color, he would be very confused.
(See https://www.ndsu.edu/pubweb/~mcclean/plsc431/mendel/mendel2.htm for snapdragon incomplete dominance example.)

I don't think Mendel got lucky; I think he worked with these plants and on these traits specifically because he noticed the patterns in them.

Because of law of dominance
Because dominant gene Express themselves and suppress effect of other gene . In case of pea  tall(t) is dominant and overrides effect of other recessive allele and does not even produces any intermediate trait.

Welcome. We require answers to be accompanied by suitable, credible answers. A little more detail and elaboration will help a lot too. It's more of a comment than an answer now.

I believe  AliceD was meaning to type: "accompanied by suitable, credible references".


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What is the science behind talent?
So some people are better at doing stuff than others of the same age..in other words, they have talent.
So I am asking, what is the science behind talent? What is different in their brains than others which give them an advantage?
By talent I mean excelling in physical performances like sports and mental abilities like IQ

This is far too broad. What kind of traits/talents are you most interested in? IQ, social skills, physical performances etc? All traits differ to what extent they are determined by genetics, environment and gene/environment interactions, and our knowledge about different traits also differ dramatically.

I agree with @fileunderwater , this question is way too broad and shows no research effort whatsoever. There is plenty of literature available on this subject. One just needs to search for it (hint, hint)..

i DID search it but couldn't find very satisfying answers. And sorry for the broad question, I narrowed it down..

Excellent. Would you perhaps care to add some of the sources to your question? I mean the ones that you came across and found unsatisfactory. It always helps to create a better understanding.


text:
Why does rotational cleavage take place in mammels like humans. What is its significance?
What is the actual reason behind the rotational cleavage that takes place in humans? Why does it happen? If it doesn't occur, what will happen


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Why should evolution not be equated with progress?
My science textbook says this:

Evolution should not be equated with progress. In fact, there is no real 'progress' in the idea of evolution. Evolution is simply the generation of diversity and the shaping of the diversity by environmental factors. The only progressive trend in evolution seems to be that more and more complex body designs have emerged over time. However, again it is not as if older designs are inefficient! So many of the older and simpler designs still survive [..] In other words, human beings are not the pinnacle of evolution, but simply yet another species in the teeming spectrum of life.

I am not sure if I agree with this; after all, humans do seem to be more advanced than dogs. Many people have asked me why I thought this was true, so here is my answer: Today, humans could wipe out dogs from Earth if they wanted, but you can hardly imagine  a scenario in which dogs would do the same to humans.
What am I missing here?

Humans more advanced than dogs?  When you consider that dogs have better hearing, a far better sense of smell, often (depending on breed) much greater endurance, a digestive system able to accept a wider variety of food...

And if you still think humans are more advanced than dogs, I'd ;like to see YOU catch a frisbee in your mouth :-)

@jamesqf yes that was a new perspective for me. Yet dogs did'nt reach Mars or Pluto, humans did.

humans are the products of 4 billions years of evolution, just like every other living organisms, so either you and e-coli are equally advanced or advancement/progress is not equal to evolution. Evolution is also quite happy to have organisms evolve in a direction that will eventually drive them extinct, as long individual selective entity does better than its competitors. Evolution is less marching in a direction and more the drunkard's walk. Any advancement is due only to chance.

@Prashant Gokhale: Well, if that's your definition of "advanced".  And strictly speaking, humans haven't reached either Mars or Pluto, machines have :-)

@John:  Arguably it's not years of evolution, but the number of generations.  So figure a human can reproduce at 16, a dog at 2, then (assuming their last common ancestor also reproduced at 2, and the divergence was smooth), dogs are 4 times as "advanced" as humans.

Actually we try hard to wipe some pests out of one square mile, and usually cannot. When we do, we wipe out a significant part of biodiversity together. Is this to be advanced?

You know you can't say that humans are more advanced than dog cause humans haven't evolved from dogs so on what basis are you saying this? These are two totally different species , I don't think that is the right way to say it .

Related question "If evolution is progress, why fight extinction"

Your argument can be easily broken down by virus. And virus is not even universally considered to be a form of life.

Rolled back edit to block quote. The quoted text is from here, and includes the odd usage.

bacteria  can survive in many place where human can’t. Ex Thermus aquaticus . It can withstand high temperature. And it has high reproductive capability.

There was a similar question like " does it create complexity" and there werent any answers. So i argued that complexity or is a side effect of survival fitness, which is enhanced by increasing numbers of attributes to cope with increasing and multifaceted geographies and an increasingly biodiverse and fit competition environment.

I'm glad you've asked the question as it is a common layman misunderstanding.
Dog vs Human
Your example comparing humans and dogs is actually very central to the logical flaw that yields many to equate evolution with progress.
There are several issues when you say

humans do seem to be more advanced than dogs

Humans are not more evolved than dogs

Humans, dogs, jellyfish, oak tree, fungi, bacteria, .... we have all evolved during about 3.5 billion years. None of the extant lineages is more evolved than any other at least in terms of the number of years of evolution. Note, however, that what matters most when considering evolutionary time is the number of generations. Humans having a rather long generation time, it tends to make fewer generations. In this regard, one could expect a dog to have been through more generations than humans and could eventually be called more evolved but even there it is not that easy. See also Are we “more evolved” than present-day bacteria?

You are a human, be aware of your biases

As @Jamesqf rightly said in the comments, you did not feel like considering the dog's extraordinary sense of smell, better hearing, higher jumps, stronger jaws or protective fur. Not to mention, dogs can typically raise way more offsprings than humans can. Not to become personal but my 8 months old, 9 kg Cocker Spaniel runs 300 meters at the same time Usain Bolt runs 200 meters! You seem to have only considered things that make you human such as opposable thumbs and high cognitive abilities. Coming to cognitive abilities you will note that a puppy learns by association faster than a baby human. Dogs just plateau much quicker than humans.
Make sure that you understand that high cognitive abilities are not a goal or a direction of evolution. While it is hard to measure the evolution of intelligence for both a question of definition and question of measurement tools, it is very very likely that many lineages (incl. eventually the Homo lineage) have evolved toward reducing intelligence at some point (see this post).
You say humans could wipe out dogs from Earth however again it feels very human (and awkwardly combative and hostile) to consider the ability to kill as a measure of progress.

The illusion of considering two variables

You consider a correlation between two variables 1) how evolved a lineage is and 2) how advanced a lineage is. (As discussed in the first point, there is actually no variance in how evolved lineages are if we consider evolutionary time). You are determining those that are more evolved by how "advanced" you visualize the lineage. Your explanatory and response variables are therefore the same and you do not explain anything by saying 'humans are both more advanced and more evolved than dogs so evolution should equate progress'

Definition of progress
A big issue in your question is the definition of progress. For example, if you define progress as an increase of mean fitness (the concept of fitness in biology has nothing to do with bodybuilding, see here) over time, then yes evolution is in part to be equated with progress as increase in mean fitness over time is exactly what natural selection is doing (see the so-called Fundamental Theorem of Natural Selection).
Evolution ≠ Natural Selection
So, let's assume we define progress as an increase in mean fitness over time. As stated in the previous section, this is exactly what natural selection is doing. So, instead of saying Evolution should not be equated with progress, one could say Natural selection is to be equated with progress (as a reminder this assumes a very specific definition of progress)
You will note that I replace the term evolution with natural selection. It is often unclear to laymen but these two terms, while related, are different.
Evolution is a change of allele (loosely speaking, an allele is a variant of a gene) frequency over time. There are a number of mechanisms that can cause evolution, one of which is natural selection (which itself is caused by a fitness differential associated with genetic variance). But there is way more to evolution than just natural selection. Genetic drift, mutations, migration and other demographic elements are all important factors causing the evolution of populations.
You should have a look at Understanding Evolution by UC Berkeley. It is a very introductory online course on evolutionary biology that will teach you about the basic forces that cause evolution.

Well said, though I'd argue one point.  Evolutionary time should not be measured in years, but in generations.  Which means that bacteria, which can produce a new generation every few hours, are far more evolutionarily advanced than us primitive chordates ;-)

It would be misleading also to consider number of generations as the quantity of evolution but I agree with your point. I try not to get into complications but I edited my post. Feel free to edit it yourself if you would think of a better way of phrasing it. Thanks.

I always thought that what you propose here as other elements are categorically different and are not the alternative to natural selection. Without mutations or migration or etc. there would not be selection, as there would not be change. And selection then would work like a filter of that change, not the component of change itself.

I always enjoy and appreciate your answers. This is another good one. I do wonder, though, about equating natural selection with progress. You define it specifically, which helps, but over time, as well as the very word progress suggests an ongoing march over many generations in a constant environment. I wouldn't expect Darwin's finches to be any more fit now than they were in 1836, or in 1831, for that matter. Environments change. Sometimes selective pressures favor large beaks, other times small.  You're more knowledgable here, but I wondered what your thoughts were.

There are two issues here; defining "progress" and equating evolution with it. I'll take the second one first.
When we "equate evolution with progress" we are typically making specific claims (sometimes without thinking about it). We mean that progress is an important priority of evolution or even its goal. We mean that evolution always leads to progress. And when we say "don't equate evolution with progress" we're saying that neither of those things is implied in the Theory of Evolution, and in fact, there isn't much evidence for either.
Humans are more advanced than dogs (again, skipping the question of defining "progress" for now), but humans and dogs aren't the only organisms around. E.coli is as much the outcome of 4 billion years of evolution as we are, yet we didn't "progress" in the same way at all.
One way of looking at it is thinking of diffusion. When I release a dot of dye into the water, it expands outward. Is there a specific force pushing it outward? Are any of the molecules trying to go outward? No, and no; all the molecules are moving randomly, and it is statistics that make it so their overall movement is outward; there simply is more space to move outside of the dot than inside.
And if I put that dye on the right edge of a water container, it would expand leftward. Again, is there a leftward force? Do all the molecules want to go left? No, and no: all the molecules are moving randomly, they just can't go further right than they already are, so for a molecule by the edge any random movement right keeps them where they are and any random movement left takes them left. And the overall average of the molecule's positions will move leftward, even though no specific molecule has a leftward bent (if they did we might expect molecules to disappear from the right edge, and in a diffusion situation they don't). Moreover, if we took the leftmost molecule at a certain point and looked at its trajectory over time, it would sure look like it's deliberately moving leftward... But that deliberateness would be an illusion; out of trillions of molecules moving randomly the odds are good that one of them would have made only or mostly leftward movements, and obviously that's the kind of molecule that would end up being leftmost in the first place. That doesn't mean it is being pushed left, or that its next movement will be leftward.
So applied to evolution, for almost all measures of "progress" we can come up with - size, intelligence, behavioral complexity, structural complexity, whatever - if evolution was pushing any lineage randomly along those variables we would still expect the maximum and even average size/intelligence/complexity to increase over time, because it would be very hard for life to become smaller, dumber or simpler than E.coli (harder but not impossible ! And we see examples of such trajectories, in parasites especially).
Now, you will tell me, evolution isn't random! Through natural selection, it leads to adaptation. True; it leads to adaptation to the environment. Change the environment, you change the direction that evolution will "push" a given lineage. And in the case of things like complexity or intelligence (the usual markers for "progress" in evolution), those traits can be adaptive or not depending on the environment; complexity allows more variety in responding to the environment, intelligence allows more productive interactions with said environment, but both have a cost, in risks of errors, in energy consumption, and so on. And so while you might say this lineage over this time period (in this environment) shows a definite trend towards complexity or intelligence (or gaining flight, or losing sight...), it is impossible to say the same of Evolution as a whole.
One point of evidence that the increase in maximum "progress level" is the result of diffusion and not a specific progress-ward force, is that as the right side of the container that still contained dye, the biosphere still contains tons of (a majority of in fact!) "un-progressed" organisms. This would not be true if Evolution as a whole were pushing toward progress. (in fact, you might note that I am not quite correct here! In a naturalistic view of abiogenesis, living things (or not-technically-living ancestors to living things) must have existed that were themselves outcomes of evolution but were incredibly simple compared to today's amazing bacteria, and those could be thought to be the lower bound in complexity, and Evolution did move life as a whole away from it! So we could argue that Evolution does move towards a minimal level of "progress" (the amount sufficient to compete against a bacterium). It's just that we reached that level over 3 billion years ago).
And to get back to the first point about defining "progress", once you dig down into what that means it can become all the clearer that evolution doesn't push one way or another. Bacteria have more metabolic diversity than Eukaryotes could hope for. Humans are more intelligent than dogs but worse at smelling. It can be argued that from a Müller's Ratchet perspective, "complexity" in Eukaryotes is pretty much constant, and any progress in one domain is the result of tradeoffs in another domain. This doesn't mean humans aren't more "advanced" than dogs, but it does demonstrate you need to be more specific about what "advanced" means for that to be true.

It is also worth mentioning one result from the long term E. Coli experiment, sample are periodically taken and frozen, and when older samples are pitted against newer ones, sometimes the older ones outcompete the younger ones. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5788700/

When you say, humans are more advanced than dogs, from what perspective are you saying that from? Is it in the capacity to use intelligence, to build and create, to do the math, to climb trees? If it is any of these, you are right: humans are better at using intelligence to build and create, at doing the math and at climbing trees than dogs do. However, from the perspective of, say, hunting down a rabbit or detecting by smell some chemical component at very low concentrations in a suitcase, dogs are indubitably better.
So which is actually more advanced? The answer is none, they are just differently adapted to be better at some things - the things they needed to be better at to survive, and which evolution created and preserved. So evolution here simply means the constant modification of living organisms and the perseverance of those who become better adapted to the conditions they live in - this means that a bacteria today is as evolved as a human being, his dog or the tree that dog is peeing on. Now when we talk about progress, we're talking about something which function or capacity improves over a continuum. Evolution does make progress sometimes, such as the progression from initial photoreceptors to the organs of vision we have today (called eyes), and the increasing capacity of some bacteria strains to resist antibiotics - both are signs of progress, and both are made possible through the process of evolution.
At a larger level, we see that life, though evolution, has been progressively more able to create more and more complex organisms (complexity here meaning the amount of information necessary to describe the organism), through the principle of "complexity allows for the creation of more complexity". Today, there are indubitably more complex organisms that there was in the beginnings of life, and yes, we can say humans are one of the most (if not the most, because of brain complexity) complex beings alive, and also complex things in the universe. So we can say that evolution is a process which made possible the progress towards more and more complex things.
What I hope to have helped understand is that evolution and progress are correlated and interdependent, but not the same thing. Evolution is a process which allows for progress, but not always and not necessarily.
I am not including any sources or background because this question relates more to etymology and meaning than scientific research.
EDIT: interesting things you may like to watch about the progress and evolution of complexity:
https://www.youtube.com/watch?v=MTFY0H4EZx4
https://school.bighistoryproject.com/bhplive
https://www.ted.com/talks/david_christian_big_history

Okay so Ill answer the questions you asked me at the beggining of the answer.

1.For hunting a rabbit, humans are undoubtedly better, we have sophisticated equipment for that.

Moreover for smelling etc, we simply use the dogs for our own use. We can control dogs and use them for our work, but  dogs simply cant control us.

@Prashant Gokhale: Really?  You obviously haven't met my dogs, have you?  You might think about who goes out to work all day, and who gets to lounge around the house :-)

@jamesqf and we're not even talking about cats yet! :p

Indeed evolution cannot be equated with progress, but that book's reasoning is misstated.
The reason it cannot be equated is because of many distinctions between these 2 concepts, regardless of the fact that in many cases evolution is a vehicle or mechanism by which progress happens, by popular definitions of what we call progress at a given time. If survival and adaptation of a species in question, is what we would consider progress in whatever context, then evolution fuels that progress, and can reasonably be said to itself be progress in that context.
Now let's say that you consider a finely balanced Ecosystem, and some species quickly evolves to better hunt another species, then from a short term perspective of the subject species, evolution is progress, but knowing that this will cause a population explosion and shortly after, mass starvation, it is clear that this was not progress, even for the hunter species -- however, it still cannot be said that evolution did not occur, so clearly evolution does not equate with progress on sematic or functional levels (the latter simply because there can be shown many situations where that is clearly not the case).
Fun aside: Also consider that evolution cannot go backwards to pick another foregone path. But in some cases that would be required for progress being considered, like the perfection of human eyeballs, which are greatly evolved, but would/could have been much better if we didn't come from the water

Evolutionary biology cannot answer a question about "progress".  Opinions are strong.  For a good discussion see https://academic.oup.com/bioscience/article/50/5/451/264248 and note comment by Stephen Jay Gould, “Progress is a noxious, culturally embedded, untestable, nonoperational, intractable idea that must be replaced if we wish to understand the patterns of history” (Gould 1988, p. 319) and William Provine “the problem is that there is no ultimate basis in the evolutionary process from which to judge true progress” (Provine 1988, p. 63).
I believe this is because its mathematical formulation only looks backward.  It presumes a parameter "fitness" which has a value in a particular environment, especially in what that environment WAS not what it IS or WILL BE.  (For a clear treatment, not the usual overbearing textbook, see Gillespie, Population Genetics - A Concise Guide, 1998 https://public.wsu.edu/~gomulki/mathgen/materials/gillespie_book.pdf )
That does not mean the question cannot be answered.  But it requires a convincing definition of progress.  There already is one in common use among futurists.  And it leads to a convincing answer.  However, there is disagreement as to whether humans are on the path to an answer.
To obtain a definition of progress, only note which forms are most likely to remain viable in future environments.
This requires forecasting of future environments, a difficulty I will pass over.  While non-trivial, it is an entirely separate question.
Looking far enough into the future, it is extremely easy to forecast that Earth (and the sun and moon and rest of it) will eventually meet some end and not even be available as an environment.  It could be as simple as a focused gamma ray burst https://jatan.space/timeline-for-life-until-the-end-of-the-universe/ .  The only viable forms will be those which have left.
There is a famous puzzle, named after Enrico Fermi though he didn't formulate the puzzle exactly.  He just asked, "Where are all the Aliens?"
Putting aside those who claim they are among us and we don't know it, and looking only at physical evidence, while some might keep themselves secret we can't think of a reason why they all would.  We appear to be alone in the universe.  There appear to be some barriers that prevent life from leaving its home planet.  And I'm not talking about the long time travels required, etc.  Those are not actually insurmountable.  I worked for NASA for 45 years and studied this question often.  Difficult is not insurmountable.  Pass over that argument, it is a sidetrack.
None of the solutions to the so-called Fermi Paradox are the least bit impressive.  Not only to me, I never met anyone who was really impressed with any of them.  They pick favorites, but everyone is puzzled.  It is not obvious humans are capable of solving this problem.  For the most concise (not too long, but still comprehensive, and very colorful) see the animated video short https://www.youtube.com/watch?v=sNhhvQGsMEc&t=6s , or look up the original paper by Michael Hart, 1975, "Explanation for the Absence of Extraterrestrials on Earth."
If in the future humans become "advanced" enough to understand the problem and work out what its realistic features are, then we might be able to say if humans can solve it, or if dogs can solve it.  So there is potential to define objective progress in evolution.
It might require the evolution of life around red dwarfs to solve the problem.  Such life might have a concept of much longer time intervals, for example, or be much more cooperative.  We just don't know how such imponderable variables would affect evolution.  The issues with life around Red Dwarfs is discussed here https://www.space.com/14659-red-dwarf-stars-planets-habitable-zones.html and note that the timeline given earlier https://jatan.space/timeline-for-life-until-the-end-of-the-universe/ suggests that in 1 trillion years Red Dwarfs will be all that is left.  Thus the future environment has already been predicted with high confidence.
The ancestors of dogs evolved in surprising ways, achieving brains that rival our own.  I'm thinking of the whales and dolphins, that presumably evolved from some predator hunting in shallow lagoons and gradually returning to the sea.  https://evolution.berkeley.edu/evolibrary/article/evograms_03
In their present form they are unsuitable for spaceships.  Suppose over a billion years the sea dried up, and they gradually adapted, developed an urgent need to free themselves from dependence on one single planet that could be so rude as to lose its oceans, and developed an instinctive collective urge to find other planets, instilling cooperation far beyond the human level.  Then dogs might win.
I personally believe the Achilles heel of the Fermi dilemma is cooperation.  Much touted human cooperation is not what it appears.  More intelligent people cooperate less.  If you explain game theory to people they cooperate less (Nash Equilibrium and all that).  A global society might not be a highly cooperative one.  Interstellar travel might require global cooperation.  Forcing everyone to take just one approach to any given problem might be the ruin of any civilization.  It is certainly not the way of evolution.
But not knowing who is going to solve the Fermi Paradox, if any species ever, does not detract from its value in defining progress in an extremely objective manner.
And if you get past that, there is the end of what we call the universe.  Cosmologists, at least some of them, now think it is not really the end.  See Dyson et. al. Disturbing Implications of a Cosmological Constant https://arxiv.org/abs/hep-th/0208013 .
But there might be ten to the 100th years of not very interesting non-entropic processes until there is a repeat, or approximate repeat, of the initial conditions, a Poincare Recurrence as Poincare proved a theorem that this would eventually happen over a hundred years ago.  Who will survive that?  We can't say it's impossible.  We know next to nothing about non-entropic processes.  But it is possible to define progress even then.

Welcome to Biology.SE! It isn't clear that this adds anything to the existing answers or that it answers the OPs question. In addition, answers are much more likely to receive a favorable response if you include supporting references (primary literature is best). Without that support, your post is indistinguishable from opinion. ——— Please take the [tour] and then consult the help pages for additional advice on [Answer] effectively on this site and then either [edit] or delete your answer accordingly. Thanks!

I added references as you requested.  But the site would not let me add more than 8 links.  This is a really crummy site (first time I've tried to post here).  I have authored over 50 peer reviewed papers in half a dozen fields.  Including links for all references is par for the course.  Clean up your act.

Welcome. Because you are new here, certain restrictions apply, including, apparently, the number of links you can add. Further, I cannot  really see how this answers the question either?

@RobertShuler — If you have constructive suggestions about the site, please feel free to start a discussion about them on [meta]. I'm not sure why you're telling me to "clean up my act". Note that I'm just another user and I am trying to help brand new users such as yourself become productive members of this community ...

There is no real progress behind the idea of evolution.
Evolution is simply the generation of diversity and shaping of diversity by environmental selection.
The only progressive trend in evolution seems to be that more and more complex body designs has emerged over time. It doesn't means that the older designs are inefficient.
However, one of the simplest form of life (Bacteria) can even survive in harsh conditions such as hot springs or ice of Antarctica.
Therefore, Human beings aren't the pinnacle of evolution, but simply yet another species in teeming spectrum of evolving life.

SOURCE: NCERT Class 10 science textbook

priyanshu, I've downvoted your answer because it is a late answer that doesn't add to the information already present in other answers. We welcome contributions from new users, though.  You might try some unanswered questions. It's best if you avoid posting answers to a previously answered question unless your answer adds something to the post.


text:
What industry job am I qualified for with a PhD in virology?
I'm considering applying for a PhD studying innate resistance to HCV. I enjoy research but I would prefer to have a stable job, instead of moving from contract to contract and writing grants to ensure that I get more funding.
Would such a PhD enable me to transition into industry? What roles would I be eligible for?

I am not sure if your question should be in Biology S.E. I feel Academia S.E. might be a better place. In addition, it seems you have a preconceived idea of what work in Academia/Industry looks like. I found myself in the exact same situation once and went for the industry. All I would say is that this old adage of job security and higher wages in the industry DOES NOT necessarily hold up in the Life Science industry. My recommendation: Do what you feel passionate about (research/money whatever you want), research companies in-depth (e.g. Glassdoor, salary surveys) before applying.


text:
Do animals exhibit handedness (paw-ness?) preference?
I have been observing my cat and found that when confronted with an unknown item, she will always use her front left paw to touch it.
This has me wondering if animals exhibit handedness like humans do? (and do I have a left handed cat?)
One note of importance is that with an unknown item, her approach is always identical, so possibly using the left paw means allowing a fast possible exit based on how she positions her body.
This question is related to Are there dextral/sinistral higher animals?. However, I question the "paw-ness" as a consequence of how the cat is approaching new items (to be ready to flee), whereas the other question remarks about the high number of "right-pawed" dogs and questions the influence of people for this preference.

It seems a shame to close this as a duplicate when theforestecologist's answer is excellent, and better than the answer on the other question.

If the questions are exact duplicates, a mod can merge them.  On Stack Overflow (my home site) it's somewhat common to close older questions as duplicates of newer ones if the new one is better.  (I haven't lurked here long enough to know the local custom.)

 Short Answer
Yes. handedness (or Behavioral Lateralization) has been documented in numerous vertebrates (mammals, reptiles and birds) as well as invertebrates.

This includes domestic cats (see Wells & Millsopp 2009).

 Long Answer
There have been numerous studies that have documented behavioral lateralization in many groups of animals including lower vertebrates (fish and amphibians), reptiles (even snakes!), birds and mammals. More recent work (e.g., Frasnelli 2013) has also shown that lateralization can also occur in invertebrates. In other words, "handedness" (or pawedness, footedness, eyedness, earedness, nostriledness,
toothedness, breastedness, gonadedness, etc.) occurs rather extensively across the animal kingdom.

These studies suggest that the evolution of brain lateralization, often linked to lateralized behaviors, may have occurred early in evolutionary history and may not have been the result of multiple independent evolutionary events as once thought.

Although this view of brain lateralization as a highly conserved trait throughout evolutionary history has gained popularity, it's still contested (reviewed by Bisazza et al. 1998; Vallortigara et al. 1999).

Note: Laterality of function may manifest in terms of preference (frequency) or performance (proficiency), with the former being far more often investigated.
And no, right-handedness is not always dominant.
But Why?

One hypothesis is that brain lateralization was the evolutionary result of the need to break up complex tasks and perform them with highly specialized neuronal units to avoid functional overlap (i.e., to account for "functional incompatibility").

In humans, many hypotheses have been developed including: division of labor, genetics, epigenetic factors, prenatal hormone exposure, prenatal vestibular asymmetry, and even ultrasound exposure in the womb.

Snake studies (see below) have suggested lateralization behavior can be dictated by environmental conditions (specifically, temperature).

Other work (Hoso et al. 2007) suggest that lateralization could be the result of convergent evolution. In this case, snakes developed feeding aparati that allow them to better consume more-common dextral species of snails.

Note: dextral (meaning "clockwise") is a type of chirality -- another form of "handedness"

Reviews:

Lateralization in non-human primates: McGrew & Marchant 1997.

Lateralized behaviors in mammals and birds:
Bradshaw & Rogers 1993; Rogers & Andrew 2002.

Lateralized behaviors in lower vertebrates: Bisazza et al. 1998; Vallortigara et al. 1999.

Some Examples:
Invertebrates

Some spiders appear to favor certain appendages for prey handling and protection (Ades & Novaes Ramires 2002).

Octopi (or octopodes) preferably use one eye over the other (Byrne et al. 2002; with seemingly no preference for right/left at the population level: Byrne et al. 2004) and also apparently have a preferred arm (Byrne et al. 2006).

Fish

Preferential ventral fin use in the gourami (Trichogaster trichopterus). [Bisazza et al. 2001].

Preferential eye use in a variety of fish species [Sovrano et al. 1999, 2001].

Amphibians

Lateralization of neural control for vocalization in frogs (Rana pipiens). [Bauer 1993].

Preferential use of hindlimbs (Robins et al. 1998), forelimbs (Bisazza et al. 1996) and eyes (Vallortigara et al. 1998) in adult anurans.

Snakes

Preferential use of right hemipenis over left under warm conditions. [Shine et al. 2000].

Coiling asymmetries were found at both the individual and population levels. [Roth 2003].

Birds

Tendency for parrots to use left-feet when feeding. [Friedmann & Davis 1938].

Mammals

Pawdness in mice. [Collins 1975].

left forelimb bias in a species of bat when using hands for climbing/grasping. [Zucca et al. 2010]

Behavior experiments show domesticated cats show strong preference to consistently use either left or right paw and that the lateralized behavior was strongly sex related (in their population: ♂ = left / ♀ = right). [Wells & Millsopp 2009].

Non-human Primates

Posture, reaching preference, tool use, gathering food, carrying, and many other tasks. See McGrew & Marchant (1997) for review.

Citations

Ades, C., and Novaes Ramires, E. (2002). Asymmetry of leg use during prey handling in the spider Scytodes globula (Scytodidae). Journal of Insect Behavior 15: 563–570.

Bauer, R. H. (1993). Lateralization of neural control for vocalization by the frog (Rana pipiens). Psychobiology, 21, 243–248.

Bisazza, A., Cantalupo, C., Robins, A., Rogers, L. J. & Vallortigara, G. (1996). Right-pawedness in toads. Nature, 379, 408.

Bisazza, A., Rogers, L. J. & Vallortigara, G. (1998). The origins of cerebral asymmetry: a review of evidence of behavioural and brain lateralization in fishes, reptiles and amphibians. Neuroscience and Biobehavioral Reviews, 22, 411–426.

Bisazza, A., Lippolis, G. & Vallortigara, G. (2001). Lateralization of ventral fins use during object exploration in the blue gourami (Trichogaster trichopterus). Physiology & Behavior, 72, 575–578.

Bradshaw, J. L. & Rogers, L. J. (1993). The Evolution of Lateral Asymmetries, Language, Tool Use and Intellect. San Diego: Academic Press.

Byrne, R.A., Kuba, M. and Griebel, U. (2002). Lateral asymmetry of eye use in Octopus vulgaris. Animal Behaviour, 64(3):461-468.

Byrne, R.A., Kuba, M.J. and Meisel, D.V. (2004). Lateralized eye use in Octopus vulgaris shows antisymmetrical distribution. Animal Behaviour, 68(5):1107-1114.

Byrne, R.A., Kuba, M.J., Meisel, D.V., Griebel, U. and Mather, J.A. (2006). Does Octopus vulgaris have preferred arms?. Journal of Comparative Psychology 120(3):198.

Collins RL (1975) When left-handed mice live in righthanded worlds. Science 187:181–184.

Friedmann, H., & Davis, M. (1938). " Left-Handedness" in Parrots. The Auk, 55(3), 478-480.

Hoso, M., Asami, T., & Hori, M. (2007). Right-handed snakes: convergent evolution of asymmetry for functional specialization. Biology Letters, 3(2), 169-173.

McGrew, W. C., & Marchant, L. F. (1997). On the other hand: current issues in and meta‐analysis of the behavioral laterality of hand function in nonhuman primates. American Journal of Physical Anthropology, 104(S25), 201-232.

Robins, A., Lippolis, G., Bisazza, A., Vallortigara, G. & Rogers, L. J. (1998). Lateralized agonistic responses and hindlimb use in toads. Animal Behaviour, 56, 875–881.

Rogers, L. J. & Andrew, R. J. (Eds) (2002). Comparative Vertebrate Lateralization. Cambridge: Cambridge University Press.

Roth, E. D. (2003). ‘Handedness’ in snakes? Lateralization of coiling behaviour in a cottonmouth, Agkistrodon piscivorus leucostoma, population. Animal behaviour, 66(2), 337-341.

Shine, R., Olsson, M. M., LeMaster, M. P., Moore, I. T., & Mason, R. T. (2000). Are snakes right-handed? Asymmetry in hemipenis size and usage in gartersnakes (Thamnophis sirtalis). Behavioral Ecology, 11(4), 411-415.

Sovrano, V. A., Rainoldi, C., Bisazza, A. & Vallortigara, G. (1999). Roots of brain specializations: preferential left-eye use during mirror-image inspection in six species of teleost fish. Behavioural Brain Research, 106, 175–180.

Sovrano, V. A., Bisazza, A. & Vallortigara, G. (2001). Lateralization of response to social stimuli in fishes: a comparison between different methods and species. Physiology & Behavior, 74, 237– 244.

Vallortigara, G., Rogers, L. J., Bisazza, A., Lippolis, G. & Robins, A. (1998). Complementary right and left hemifield use for predatory and agonistic behaviour in toads. NeuroReport, 9, 3341–3344.

Vallortigara, G., Rogers, L. J. & Bisazza, A. (1999). Possible evolutionary origins of cognitive brain lateralization. Brain Research Reviews, 30, 164–175.

Wells, D. L., & Millsopp, S. (2009). Lateralized behaviour in the domestic cat, Felis silvestris catus. Animal Behaviour, 78(2), 537-541.

Zucca, P., Palladini, A., Baciadonna, L. and Scaravelli, D. (2010). Handedness in the echolocating Schreiber's long-fingered bat (Miniopterus schreibersii). Behavioural processes, 84(3): 693-695.

Holy c...bologna! That's a lot of citations, even for SE standards!

To add to the list: octopodes also have their preferred arm.

@JanDvorak if you can supply a reputable source, I will gladly add it to my answer :)

Quick search suggests an article at nature.com, but its external links don't work. #2 is a paper at PubMed that I haven't bought. #4 looks promising but I didn't check the site it's published on,  but it seems to be the same paper as #2 offers for purchase. ScienceDirect hosts a different paper as well as a video but they seem to be mostly about movement.

I was actually looking for references for handedness in elephants, that i remembered. Surprisingly I found this science blog, stating that handedness is actually rare in animals.

Lateralization has also been shown in mother-infant interactions (left side of mother bias) in diverse mammal species, purportedly due to right brain hemisphere social processing Lateralization of mother–infant interactions in a diverse range of mammal species

Horses also display handedness in their gaits: http://www.equine-rehab.com/handedness-in-horses/  Also, they show it in their manes, which naturally fall either to the left or right side of their neck.  No idea whether that correlates to their gait, though.

Polishing up your laureate work :D -- Adding links to that endless reference list of yours may improve the A further ;-)

@theforestecologist, does the fact that southpaws are in the minority (10% globally) mean that lefties are sexually undesirable? Arigato gozaimus in advance. Great answer!

Another fun example of handedness/chirality: Portuguese man o' war have dimorphic populations with ~50% having their sail ("pneumatophore") pointing left and 50% leaning right. When winds blow these organisms, this dimorphism ensures that at least some will not be randomly blown ashore to die. (Source: Wikipedia).  Evolution is fun :)

Stanley Coren, The Lefthander Syndrome, says that humans are distinctive, not in having preferred handedness, but in having a high majority of individuals right-sided instead of odds approaching 50-50.
There is a lot of urban legend biology that might be answered. For instance, right-handedness is a human combat advantage, because a right-handed attack or defense puts the heart slightly further away from an opponent than an attack that's left-handed. And that one doesn't require a real knowledge of biology to answer: 48% of Olympic fencers are left-handed, and among people who've studied it left-handed people are far more likely to be excellent at combat sports than right-handed people.
(I'd love to see someone debunk the array of folk explanations for why a large majority of humans are right-handed.)

Maybe it also swayed that way because humans co-operate a lot: I am left handed and as an experiment, I decided for a couple weeks to do interactions, when buying items, etc, as a right handed; it was amazing how much smoother everything was, just hands meeting one another to exchange an item alone was noticeably more direct than me interacting as a lefty; with that, it is possible that babies start to go the more convenient path, reinforcing the right handed majority; I highly recommend that experiment, it’s simple, fun and interesting.

If by answer you mean 'debunk', then this is consistent. Otherwise, you'd be saying that right-handed people have a combat advantage and left-handed people are better at combat sports, which wouldn't follow. I'm not sure which one it is.


text:
Source for an upper bound in the number of genes based on mutation rates
So I've found myself referring in an answer once again to the idea that complexity (insofar as it's a quantity for which "number of genes" is a proxy) has an upper bound, limited by Muller's ratchet-related processes. The idea being that if harmful mutations happen faster than natural selection can cull them, the genome will accumulate harmful mutations and the organisms' fitness will degrade over time; and that this imposes an upper bound on the size of a functional genome, because the number of harmful mutations that can happen obviously depends on the size of the functional genome (i.e. how many bases there are where a mutation would likely be harmful).
I knew about Muller's Ratchet, and when referring to it I usually refer to the Wikipedia page for it. But I first came across the concept that this defined an upper bound on complexity (as opposed to being a huge paradox of evolution and a plausible reason for sexual reproduction) in this Less Wrong post (it might have been edited since I first read it).
I've pretty much adopted this concept as a thing that happens; it makes sense to me, and I have seen other references to such an upper bound limited by mutation rates from biologists, for example most recently in this talk by Nick Lane (at 39:15).
However whenever I talk about this in discussions or debates and look for sources I cannot find an easy-to-link source that presents this argument, as seen from within the field of biology. The Wikipedia page on Muller's ratchet only talks about it in the context of asexual reproduction and LessWrong isn't a biology source. The post claims that George Williams makes this argument in his book Adaptation and Natural Selection, and that may also be what Nick Lane is referring to in the video, but a book is hard to refer to online and I would expect such a powerful concept to have more material about it anyway.
Is this concept actually the consensus in the field of biology, or evolutionary biology failing that? Either way, where can I find good, preferably linkable, sources explaining the concept or debating it if it isn't the consensus?

Muller's ratchet is a process that depends upon the population size. What population size are you willing to consider? The question will be a bit hard to address I am afraid but you might want to search the literature for the terms '[mutational meltdown]', 'mutation load' (see this post on the maximum number of babies possible) and 'drift load'.

Btw, please realize that a proxy should be a correlated variable, not a definition. What I mean is that if you don't clearly define complexity, it sounds funny to consider having a proxy for it rather than considering that you define complexity as being the number of genes. Of course many people will not find intuitive to define complexity as the number of genes also that might make some crop botanist happy :)

@Remi.b I know what a proxy is and I used the word correctly. I didn't define "complexity" in my post at all, deliberately so, but the most exact expression of what I meant would be "there are many concepts, some well-defined others vague, associated with the word 'complexity' in biology, a subset of which can be considered a quantity correlated with gene number such that gene number can be used as a proxy for it (whether specifically and vaguely), and when I use the word "complexity" here I am referring to any member of that subset".

To clarify; you are specifically asking for sources that discuss Muller's ratchet in relation to an upper bound for complexity?

@fileunderwater Yes. I hope that is clear enough, if not I would still be happy with whatever you think I meant, if nothing else it would help me know what I need to clarify.

@RozennKeribin No, that is fine. I just wanted to make sure that you weren't asking about the mutational load-aspects of Muller's ratchet, which are more well known and discussed. Finding papers/references that cover those aspects would be easier (but less interesting). You could maybe put the man question closer to the top, since the Q is quite long.