Neoteny in humans

The human head becomes proportionately smaller and the legs become proportionately longer as humans mature. This implies that proportionately large heads and proportionately short legs would be neotenous features for adults.

Neoteny is the retention of juvenile traits well into adulthood. In humans, this trend is greatly amplified, especially when compared to non-human primates. Neotenic features of the head include the globular skull;[1] thinness of skull bones;[2] the reduction of the brow ridge;[3] the large brain;[3] the flattened[3] and broadened face;[2] the hairless face;[4] hair on (top of) the head;[1] larger eyes;[5] ear shape;[1] small nose;[4] small teeth;[3] and the small maxilla (upper jaw) and mandible (lower jaw).[3]

Neoteny of the human body is indicated by glabrousness (hairless body).[3] Neoteny of the genitals is marked by the absence of a baculum (penis bone);[1] the presence of a hymen;[1] and the forward-facing vagina.[1] Neoteny in humans is further indicated by the limbs and body posture, with the limbs proportionately short compared to torso length;[2] longer leg than arm length;[6] the structure of the foot;[1] and the upright stance.[7][8]

Humans also retain a plasticity of behavior that is generally found among animals only in the young. The emphasis on learned, rather than inherited, behavior requires the human brain to remain receptive much longer. These neotenic changes may have disparate roots. Some 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, though these peramorphic traits separating modern humans from extant chimpanzees were present in Homo erectus to an even higher degree than in Homo sapiens, which means general neoteny is valid for the H. erectus to H. sapiens transition (although there were perimorphic changes separating H. erectus from even earlier hominins such as most Australopithecus).[9] Later research shows that some species of Australopithecus, including Australopithecus sediba, had the non-neotenic traits of H. erectus to at least the same extent which separate them from other Australopithecus, making it possible that general neoteny applies throughout the evolution of the genus Homo depending on what species of Australopithecus that Homo descended from. The type specimen of A. sediba had these non-neotenic traits, despite being a juvenile, suggesting that the adults may have been less neotenic in these regards than any H. erectus or other Homo.[10]

  1. ^ a b c d e f g Bednarik RG (2011). The Human Condition. doi:10.1007/978-1-4419-9353-3. ISBN 978-1-4419-9352-6. (page 134), cited by:
    Achrati A (November 2014). "Neoteny, female hominin and cognitive evolution". Rock Art Research. 31 (1): 232–238.
    "In humans, neoteny is manifested in the resemblance of many physiological features of a human to a late-stage foetal chimpanzee. These foetal characteristics include hair on the head, a globular skull, ear shape, vertical plane face, absence of penal bone (baculum) in foetal male chimpanzees, the vagina pointing forward in foetal ape, the presence of hymen in neonate ape, and the structure of the foot. 'These and many other features', Bednarik says, 'define the anatomical relationship between ape and man as the latter's neoteny'".
  2. ^ a b c Gould SJ (1977). Ontogeny and Phylogeny. Cambridge: Belknap Press.
  3. ^ a b c d e f Montagu A (1989). Growing Young (2nd ed.). Granby, MA: Bergin & Garvey Publishers. ISBN 978-0-89789-167-7. Retrieved 19 July 2019.
  4. ^ a b Jean-Baptiste de Panafieu P (2007). Evolution. USA: Seven Stories Press. ISBN 978-1-60980-368-1.
  5. ^ "Why Do Men Find Women With Larger Eyes Attractive?". Zidbits - Learn something new everyday!. 2 June 2011.
  6. ^ Smith JM (1958). The Theory of Evolution. Cambridge University Press.
  7. ^ Henke W, Tattersall W, eds. (2007). Handbook of Paleoanthropology. Vol. 1. NY: Springer Books. ISBN 978-3-540-33761-4.
  8. ^ Hetherington R (2010). The Climate Connection: Climate Change and Modern Human Evolution. Cambridge University Press. ISBN 978-0-521-14723-1.
  9. ^ Thompson JL, Krovitz GE, Nelson AJ, eds. (December 2003). Patterns of Growth and Development in the Genus Homo. Cambridge University Press. ISBN 978-0-511-54256-5.
  10. ^ Reed KE, Fleagle JG, Leakey RE, eds. (March 2013). The paleobiology of Australopithecus. Vertebrate Paleobiology and Paleoanthropology. Netherlands: Springer. ISBN 978-94-007-5919-0.