question: Why do insects, fish, amphibians, birds etc have seemingly infinite variations of the species...but humans are pretty much black, white, or yellow, and homogenous comparatively?
comment: Human is one specific species of animal and you compare them to a whole family. To make a fair comparaison you should compare fish, amphibians or bird vs mammals. And there is a lot of variations of species for mammals too. The skin color of human is just one variation within the same species, just like height or color of hair. In that case, it would seem that human are more variable. Take for example black or brown bear, both are different species, while human with brown or white skin are still of the same species.
passages: Blackfoot disease is a disease caused by environmental pollution and causes people to have black, charcoal-like skin in the lower limbs. This is caused by arsenic pollution in water and food source. This is an example of how disease can affect human variation. Another disease that can affect human variation is syphilis, a sexual transmitted disease. Syphilis does not affect human variation until the middle stage of the disease. It then starts to grow rashes all over the body, affecting people's human variation.
  
  Section::::Environmental factors.:Nutrition.
   Many species, such as all marine mammals, the owl monkey and the Australian sea lion (pictured at right) are monochromats under normal conditions. In humans, absence of color discrimination or poor color discrimination is one among several other symptoms of severe inherited or acquired diseases, as for example inherited achromatopsia, acquired achromatopsia or inherited blue cone monochromacy.
  
  Section::::Humans.
   One hallmark feature of the Order Primates is the diminished emphasis on olfaction. Smell is often viewed as a mitigated special sense during the emergence of higher neural function, and correspondingly, olfaction has been increasingly reduced throughout the course of primate evolution. Some researchers relate the de-emphasis of smell to the emergence of complex vision. Accordingly, many primate species convey a large proportion of OR pseudogenes, with the highest levels shown in humans, chimpanzees, and gorillas. Humans only contain approximately 400 functional genes, contrasted with the 600 OR pseudogenes present within the genome. The disparity is explained by the development of acute vision in Catarrhini (apes and Old World monkeys) 40 million years ago, namely during the period when the Earth became cooler. Trichromatic vision was evolved to enhance long-distance perception and foraging for ripe fruit, reducing the selective advantage of possessing a large OR gene repertoire.
   Human skin shows high skin color variety from the darkest brown to the lightest pinkish-white hues. Human skin shows higher variation in color than any other single mammalian species and is the result of natural selection. Skin pigmentation in humans evolved to primarily regulate the amount of ultraviolet radiation (UVR) penetrating the skin, controlling its biochemical effects.
   Other important factors of environmental factors include climate and disease. Climate has effects on determining what kinds of human variation are more adaptable to survive without much restrictions and hardships. For example, people who live in a climate where there is a lot of exposure to sunlight have a darker color of skin tone. Evolution has caused protection of folate (folic acid) from UV radiation, thus giving them darker skin tone with more melanin to make sure child development is smooth and successful. Conversely, people who live farther away from the equator have a lighter skin tone. This is due to a need for an increased exposure and absorbance of sunlight to make sure the body can produce enough vitamin D for survival.
   Humans and some other mammals have evolved trichromacy based partly on pigments inherited from early vertebrates. In fish and birds, for example, four pigments are used for vision. These extra cone receptor visual pigments detect energy of other wavelengths, including sometimes ultraviolet. Eventually two of these pigments were lost (in placental mammals) and another was gained, resulting in trichromacy among some primates. Humans and closely related primates are usually trichromats, as are some of the females of most species of New World monkeys, and both male and female howler monkeys.
   Among human beings, the sense of sight is usually in charge of recognizing other members of the same species, with maybe the subconscious help of smell. In particular, the human brain has a disproportionate amount of processing power dedicated to finely analyze the features of a human face. This is why we are able to distinguish basically all six billions of human beings from each other (barring look-alikes), and a human being from a similar species like some anthropomorphic ape, with only a quick glance.
   The basis for this variation is the number of cone types that differ between species. Mammals in general have color vision of a limited type, and usually have red-green color blindness, with only two types of cones. Humans, some primates, and some marsupials see an extended range of colors, but only by comparison with other mammals. Most non-mammalian vertebrate species distinguish different colors at least as well as humans, and many species of birds, fish, reptiles and amphibians, and some invertebrates, have more than three cone types and probably superior color vision to humans.
   Human skin color
  
  Human skin color ranges in variety from the darkest brown to the lightest hues. An individual's skin pigmentation is the result of genetics, being the product of both of the individual's biological parents' genetic makeup, and exposure to sun. In evolution, skin pigmentation in human beings evolved by a process of natural selection primarily to regulate the amount of ultraviolet radiation penetrating the skin, controlling its biochemical effects.
   Humans are distributed across the globe with the exception of Antarctica, and form a variable species. In adults, average weight varies from around 40 kilos for the smallest and most lightly built tropical people to around 80 kilos for the heavier northern peoples. Size also varies between the sexes, the sexual dimorphism in humans being more pronounced than that of chimpanzees, but less than the dimorphism found in gorillas. The colouration of skin, hair and eyes also varies considerably, with darker pigmentation domination in tropical climates and lighter in polar regions.
  
  BULLET::::- Genetic, ethnic affiliation, geographical ancestry.
   Guido Barbujani has written that human genetic variation is generally distributed continuously in gradients across much of Earth, and that there is no evidence that genetic boundaries between human populations exist as would be necessary for human races to exist.
  
  Over time, human genetic variation has formed a nested structure that is inconsistent with the concept of races that have evolved independently of one another.
  
  Section::::Modern scholarship.:Social constructions.
   Human phenotypes are highly polygenic (dependent on interaction by many genes) and are influenced by environment as well as by genetics.
  
  Nucleotide diversity is based on single mutations, single nucleotide polymorphisms (SNPs). The nucleotide diversity between humans is about 0.1 percent (one difference per one thousand nucleotides between two humans chosen at random). This amounts to approximately three million SNPs (since the human genome has about three billion nucleotides). There are an estimated ten million SNPs in the human population.
   With the evolution of hairless skin, abundant sweat glands, and skin rich in melanin, early humans could walk, run, and forage for food for long periods of time under the hot sun without brain damage due to overheating, giving them an evolutionary advantage over other species. By 1.2 million years ago, around the time of "Homo ergaster", archaic humans (including the ancestors of "Homo sapiens") had exactly the same receptor protein as modern sub-Saharan Africans.
   Richard Jantz and Lee Meadows Jantz who are both directors at the Forensic Anthropology Center at the University of Tennessee said white American skulls of both sexes have become less neotenous since the mid-19th century.
  
  Section::::Between races, ethnicities and among primates.:Aboriginal Australians.
  
  Frederick S. Hulse wrote in 1962 that aboriginal Australians have retained "similar" "skeletal characteristics" to those "which most men possessed in earlier times" (gerontomorphic characteristics) that are "contrary" to the "pedomorphic qualities" which the Bushmen have evolved.
  
  Section::::Between races, ethnicities and among primates.:Mongoloids.
   Approximately 10% of the variance in skin color occurs within regions, and approximately 90% occurs between regions. Because skin color has been under strong selective pressure, similar skin colors can result from convergent adaptation rather than from genetic relatedness; populations with similar pigmentation may be genetically no more similar than other widely separated groups. Furthermore, in some parts of the world where people from different regions have mixed extensively, the connection between skin color and ancestry has substantially weakened. In Brazil, for example, skin color is not closely associated with the percentage of recent African ancestors a person has, as estimated from an analysis of genetic variants differing in frequency among continent groups.
   Patterns such as those seen in human physical and genetic variation as described above, have led to the consequence that the number and geographic location of any described races is highly dependent on the importance attributed to, and quantity of, the traits considered. Scientists discovered a skin-lighting mutation that partially accounts for the appearance of Light skin in humans (people who migrated out of Africa northward into what is now Europe) which they estimate occurred 20,000 to 50,000 years ago. The East Asians owe their relatively light skin to different mutations. On the other hand, the greater the number of traits (or alleles) considered, the more subdivisions of humanity are detected, since traits and gene frequencies do not always correspond to the same geographical location. Or as put it:
   Humans have undergone an extraordinary loss of olfactory receptor genes during our recent evolution, which explains our relatively crude sense of smell compared to most other mammals. Evolutionary evidence suggests that the emergence of color vision in humans and several other primate species has diminished the need for the sense of smell.
  
  In September 2016, scientists reported that, based on human DNA genetic studies, all non-Africans in the world today can be traced to a single population that exited Africa between 50,000 and 80,000 years ago.
  
  Section::::Mitochondrial DNA.
   The Negro race... is marked by black complexion, crisped of woolly hair, compressed cranium and a flat nose, The projection of the lower parts of the face, and the thick lips, evidently approximate it to the monkey tribe: the hordes of which it consists have always remained in the most complete state of barbarism.
  
  Cuvier's racial studies held the main features of polygenism which are as follows:
  
  BULLET::::- Fixity of species
  
  BULLET::::- Strict limits on environmental influence
  
  BULLET::::- Unchanging underlying type
  
  BULLET::::- Anatomical and cranial measurement differences in races
  
  BULLET::::- Physical and mental differences between racial worth
   Craig Venter and Francis Collins of the National Institute of Health jointly made the announcement of the mapping of the human genome in 2000. Upon examining the data from the genome mapping, Venter realized that although the genetic variation within the human species is on the order of 1–3% (instead of the previously assumed 1%), the types of variations do not support notion of genetically defined races. Venter said, "Race is a social concept. It's not a scientific one. There are no bright lines (that would stand out), if we could compare all the sequenced genomes of everyone on the planet." "When we try to apply science to try to sort out these social differences, it all falls apart."
   The understanding of the genetic mechanisms underlying human skin color variation is still incomplete, however genetic studies have discovered a number of genes that affect human skin color in specific populations, and have shown that this happens independently of other physical features such as eye and hair color. Different populations have different allele frequencies of these genes, and it is the combination of these allele variations that bring about the complex, continuous variation in skin coloration we can observe today in modern humans. Population and admixture studies suggest a 3-way model for the evolution of human skin color, with dark skin evolving in early hominids in sub-Saharan Africa and light skin evolving independently in Europe and East Asia after modern humans had expanded out of Africa.
   Variation comes from mutations in the genome, reshuffling of genes through sexual reproduction and migration between populations (gene flow). Despite the constant introduction of new variation through mutation and gene flow, most of the genome of a species is identical in all individuals of that species. However, even relatively small differences in genotype can lead to dramatic differences in phenotype: for example, chimpanzees and humans differ in only about 5% of their genomes.
  
  Section::::Variation.:Mutation.
   In 2006, Lewontin wrote that any genetic study requires some priori concept of race or ethnicity in order to package human genetic diversity into a defined, limited number of biological groupings. Informed by genetics, zoologists have long discarded the concept of race for dividing groups of non-human animal populations within a species. Defined on varying criteria, in the same species a widely varying number of races could be distinguished. Lewontin notes that genetic testing revealed that "because so many of these races turned out to be based on only one or two genes, two animals born in the same litter could belong to different 'races'".
   A 2002 study found that about 13% of human craniometric variation existed between regions, while 81% existed within regions (the other 6% existed between local populations within the same region). In contrast, the opposite pattern of genetic variation was observed for skin color (which is often used to define race), with 88% of variation between regions. The study concluded that "The apportionment of genetic diversity in skin color is atypical, and cannot be used for purposes of classification."
   in some non-human species this polymorphic variation is even greater, and it may well be adaptive.
  
  Section::::Physiology of color perception.:Theories.
   Human genetic variation
  
  Human genetic variation is the genetic differences in and among populations. There may be multiple variants of any given gene in the human population (alleles), a situation called polymorphism.
  
  No two humans are genetically identical. Even monozygotic twins (who develop from one zygote) have infrequent genetic differences due to mutations occurring during development and gene copy-number variation. Differences between individuals, even closely related individuals, are the key to techniques such as genetic fingerprinting.
  
  As of 2017, there are a total of 324 million known variants from sequenced human genomes.
  
presuppositions: Humans are a single species. Humans are relatively homogenous.
corrections: Humans are extremely varied sometimes in more ways than animals that are different species.  Humans are very variable depending on the type of variation.
raw_presuppositions: Humans are a single species. Humans are relatively homogenous.
raw_corrections: Humans are extremely varied sometimes in more ways than animals that are different species.  Humans are very variable depending on the type of variation.