Neoteny in humans

Neoteny in humans is the slowing or delaying of body development, compared to non-human primates, resulting in features such as a large head, a flat face, and relatively short arms and legs. These neotenic changes may have been brought about by sexual selection in human evolution. In turn, they may have permitted the development of human capacities such as emotional communication. However, humans also have relatively large noses and long legs, both peramorphic (not neotenic) traits.

In humans, neotenic traits include several features of the head, including the globular skull thinness of skull bones; the reduction of the brow ridge; the large brain; the flattened and broadened face; the hairless face; hair on (top of) the head; larger eyes; ear shape; small nose; small teeth; and the small maxilla (upper jaw) and mandible (lower jaw).

Neoteny of the human body is indicated by glabrousness (hairless body). Neoteny of the genitals is marked by the absence of a baculum (penis bone); the presence of a hymen; and the forward-facing vagina. Neoteny in humans is further indicated by the limbs and body posture, with the limbs proportionately short compared to torso length; longer leg than arm length; the structure of the foot; and the upright stance.

Many prominent evolutionary theorists propose that neoteny has been a key feature in human evolution. Stephen Jay Gould believed that the "evolutionary story" of humans is one where we have been "retaining to adulthood the originally juvenile features of our ancestors".J. B. S. Haldane mirrors Gould's hypothesis by stating a "major evolutionary trend in human beings" is "greater prolongation of childhood and retardation of maturity."Delbert D. Thiessen said that "neoteny becomes more apparent as early primates evolved into later forms" and that primates have been "evolving toward flat face." However, in light of some groups using arguments based around neoteny to support racism, Gould also argued "that the whole enterprise of ranking groups by degree of neoteny is fundamentally unjustified" (Gould, 1996, pg. 150).

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