question: Why do animals get to full grown adult size so much faster than humans?
comment: Depends on species and much on life span. Take lions. They don't live much more than 12-15 years. So they are adult in 3-4 years. Tiger shark, which lives to over 35-40 years, doesn't get large until about 10 years (and grows its entire life).
passages: In developed countries, infants are typically in weight and in height at birth. However, low birth weight is common in developing countries, and contributes to the high levels of infant mortality in these regions. Helpless at birth, humans continue to grow for some years, typically reaching sexual maturity at 12 to 15 years of age. Females continue to develop physically until around the age of 18, whereas male development continues until around age 21. The human life span can be split into a number of stages: infancy, childhood, adolescence, young adulthood, adulthood and old age. The lengths of these stages, however, have varied across cultures and time periods. Compared to other primates, humans experience an unusually rapid growth spurt during adolescence, where the body grows 25% in size. Chimpanzees, for example, grow only 14%, with no pronounced spurt. The presence of the growth spurt is probably necessary to keep children physically small until they are psychologically mature. Humans are one of the few species in which females undergo menopause. It has been proposed that menopause increases a woman's overall reproductive success by allowing her to invest more time and resources in her existing offspring, and in turn their children (the grandmother hypothesis), rather than by continuing to bear children into old age.
   Dogs are highly variable in height and weight. The smallest known adult dog was a Yorkshire Terrier that stood only at the shoulder, in length along the head and body, and weighed only . The largest known adult dog was an English Mastiff which weighed and was from the snout to the tail. The tallest known adult dog is a Great Dane that stands at the shoulder.
   Several reasons for this trend are possible, one of which is that neural cells have a relative constant size. Some brain functions, like the brain pathway responsible for a basic task like drawing breath, are basically similar in a mouse and an elephant. Thus, the same amount of brain matter can govern breathing in a large or a small body. While not all control functions are independent of body size, some are, and hence large animals need comparatively less brain than small animals. This phenomenon can be described by an equation: C" = "E"/"S, where E and S are brain and body weights respectively, and C is called the cephalization factor. To determine the value of this factor, the brain- and body-weights of various mammals were plotted against each other, and the curve of "E" = "C""S" chosen as the best fit to that data.
   Other theorists have argued that neoteny has not been the main cause of human evolution, because humans only retain some juvenile traits, while relinquishing others. For example, the high leg-to-body ratio (long legs) of adult humans as opposed to human infants shows that there is not a holistic trend in humans towards neoteny when compared to the other great apes. Andrew Arthur Abbie agrees, citing the gerontomorphic fleshy human nose and long human legs as contradicting the neoteny hominid evolution hypothesis, although he does believe humans are generally neotenous. Brian K. Hall also cites the long legs of humans as a peramorphic trait, which is in sharp contrast to neoteny.
   Physical anthropologist Barry Bogin said that the pattern of children's growth may intentionally increase the duration of their cuteness. Bogin said that the human brain reaches adult size when the body is only 40 percent complete, when "dental maturation is only 58 percent complete" and when "reproductive maturation is only 10 percent complete". Bogin said that this allometry of human growth allows children to have a "superficially infantile" appearance (large skull, small face, small body and sexual underdevelopment) longer than in other "mammalian species". Bogin said that this cute appearance causes a "nurturing" and "care-giving" response in "older individuals".
   Shorter gestation lengths are found in the greater short-nosed fruit bat ("Cynopterus sphinx") with a period of three months. The litter size of all megabats is usually one offspring.
   Section::::Human evolution.:Growth pattern of children.
  
  Desmond Collins who was an Extension Lecturer of Archaeology at London University said that the lengthened youth period of humans is part of neoteny.
   BULLET::::- The largest hutia are Desmarest's Hutia ("Capromys pilorides") of Cuba , a tail that is long, and weigh . The largest extinct Blunt-toothed giant hutia to have weighed between 50 and 200 kg (110 and 440 lb).
  
  BULLET::::- The largest Muroid is the Gambian pouched rat of Africa. It grows up to in total length and can weigh up to .
   BULLET::::- The largest possum is the common brushtail possum ("Trichosurus vulpecula") from Australia 32–58 cm with a tail length of 24–40 cm. It weighs 1.2-4.5 kg. Males are generally larger than females.
   Brain size usually increases with body size in animals (is positively correlated), i.e. large animals usually have larger brains than smaller animals. The relationship is not linear, however. Generally, small mammals have relatively larger brains than big ones. Mice have a direct brain/body size ratio similar to humans (1/40), while elephants have a comparatively small brain/body size (1/560), despite being quite intelligent animals.
   Development at birth varies considerably among animals, and even among mammals. Altricial species are relatively helpless at birth and require considerable parental care and protection. In contrast, precocial animals are born with open eyes, have hair or down, have large brains, and are immediately mobile and somewhat able to flee from, or defend themselves against, predators. Primates are precocial at birth, with the exception of humans.
  
  The duration of gestation in placental mammals varies from 18 days in jumping mice to 23 months in elephants. Generally speaking, fetuses of larger land mammals require longer gestation periods.
   BULLET::::- The majority of mammals are born with a brain close to 90% of the adult weight. Humans are born with 28% of the adult weight, chimpanzees with 54%, bottlenose dolphins with 42.5%, and elephants with 35%.
   Section::::Development.
  
  The neomammalian brain (neocortex) is the newest addition to the Human Brain. MacLean proposed that as animals evolved over the hundreds of millions of years , in order for an increased chance of survival, higher order animals developed an increased cognitive ability, which resulted in an increase in brain size. 
   At the opposite end of the spectrum are precocial animals in which the young have open eyes, have hair or down, have large brains, and are immediately mobile and somewhat able to flee from, or defend themselves against, predators. For example, with ground-nesting birds such as ducks or turkeys, the young are ready to leave the nest in one or two days. Among mammals, most ungulates are precocial, being able to walk almost immediately after birth. Beyond the precocial are the superprecocial animals, such as the megapode birds, which hatch with full flight feathers.
  
  Section::::Basis.
   Brain size usually increases with body size in animals (i.e. large animals usually have larger brains than smaller animals); the relationship is not, however, linear. Small mammals such as mice may have a brain/body ratio similar to humans, while elephants have a comparatively lower brain/body ratio.
   Physiological prematurity
  
  The term physiological prematurity refers to the fact that compared to most animals, humans are born in a premature biological state. Although sensory organs and skeletal and muscular systems are largely developed prenatally, human babies at the time of their birth are completely helpless and dependent on intensive care. This is in contrast to the maturity at birth found in other higher mammals (e.g. elephants, horses). 
   Section::::Smallest adult size.:Male dwarfism.
   The process of insular dwarfing can occur relatively rapidly by evolutionary standards. This is in contrast to increases in maximum body size, which are much more gradual. When normalized to generation length, the maximum rate of body mass decrease during insular dwarfing was found to be over 30 times greater than the maximum rate of body mass increase for a ten-fold change in mammals. The disparity is thought to reflect the fact that pedomorphism offers a relatively easy route to evolve smaller adult body size; on the other hand, the evolution of larger maximum body size is likely to be interrupted by the emergence of a series of constraints that must be overcome by evolutionary innovations before the process can continue.
   Increased postcanine size can be correlated with the evolution of other physiological traits
   Utilization of endocranial volume as a measure for brain size has been a popular methodology with the fossil record since Darwin in the mid 1800s. This measure has been used to access the metabolic requirements for brain growth and the subsequent trade-offs.
  
  Section::::Human and primate development.:Neoteny.
   Furthermore, the changes in the structure of human brains may be even more significant than the increase in size.
   Brain to body size scales allometrically. Small bodied mammals have relatively large brains compared to their bodies whereas large mammals (such as whales) have smaller brain to body ratios. If brain weight is plotted against body weight for primates, the regression line of the sample points can indicate the brain power of a primate species. Lemurs for example fall below this line which means that for a primate of equivalent size, we would expect a larger brain size. Humans lie well above the line indicating that humans are more encephalized than lemurs. In fact, humans are more encephalized than all other primates.
   In 1926 Louis Bolk described neoteny as the major process in humanization. In his 1977 book "Ontogeny and Phylogeny", Steven Jay Gould noted that Bolk's account constituted an attempted justification for "scientific" racism and sexism, but acknowledged that Bolk had been right in the core idea that humans differ from other primates in becoming sexually mature in an infantile stage of body development.
  
  Section::::In humans.
   BULLET::::- The kiwi lays the largest egg of any bird relative to its size - up to a quarter of the mass of the female.
  
  BULLET::::- Shrews have the largest brain-to-body mass ratio of any animal, with brains that are 10% of body weight. Humans however have the largest encephalization quotient of any animal.
  
  Section::::Humans.
  
  BULLET::::- The longest bone in the human body is the femur.
  
  BULLET::::- The largest artery is the aorta and the largest vein is the inferior vena cava.
   In terms of brain size differences, it has been noted that given the larger skull in neoteny humans, brain volume may be larger than an average human brain. It has been hypothesized that this is one mode of which the brains of Homosapiens grew as a species, as the prolonged development of neurons may have lead to hypermorphosis, or excessive neuronal growth.Especially in the prefrontal cortex, brain pruning from childhood may be slower than usual, allowing for more time for neuronal maturation. This prolongs the transformation of otherwise very juvenile features.
  
presuppositions: All animals grow to full adult size much faster than humans. Animals uniformly get to adult size faster than humans.
corrections: Some animals grow to full adult size much faster than humans. The rate of an animal's growth depends on its species and lifespan, and is not uniform.
raw_presuppositions: All animals grow to full adult size much faster than humans. Animals uniformly get to adult size faster than humans.
raw_corrections: Some animals grow to full adult size much faster than humans. The rate of an animal's growth depends on its species and lifespan, and is not uniform.