Neoteny in a young ape
Amphibians begin life in the water as tadpoles but as adults spend most of their time on land. But a Mexican salamander found life in the water more comfortable than the struggle on land and a neotenous change occurred to adapt it for such a life. It kept all the features of its tadpole stage into adult life and actually breeds and lives its whole life now as a large tadpole. It is the axolotl. We know for sure it is a neotenous salamander because it can be induced to undergo the metamorphosis that it normally postpones for life and the result is an ordinary looking salamander.
Neoteny is a mechanism for rapid adaptation to changing conditions and succeeds because juveniles are usually less specialized than adults. A minor change to a gene controlling development is all that is needed to delay growing up.
It seems to have worked strongly in man’s evolution. Those who dislike the aquatic theory say that neoteny is all that is needed to explain the changes in the developing ape. If so, what unusual conditions required neotenous changes in an ape setting out to explore the grasslands? Evidently none. The baboon successfully made the same transition without invoking neoteny. Indeed its snout lengthened compared with an ordinary monkey rather than remaining flat like the foetal baboon’s. Nor did they lose their body hair as mankind did. Admittedly, man is not really the “naked ape” because he has as many hair follicles per unit area as any other great ape. Human beings look naked because human hairs are so short and so fine that, to all intents and purposes, human beings are naked. Why should a savannah ape be effectively naked? What is the reason for human nakedness?
Some anthropologists argue that by shedding hair our ancestors were able to keep cooler whilst hunting. Who then did the hunting? Human females? Female humans have lost more hair than male humans. And if nakedness solved the problem of overheating, why did other mammals not adapt in the same way? Other primates which took to the grasslands when the Miocene forests retreated, like vervet monkeys as well as baboons, did not find it necessary to lose their hair. Indeed, why, if nakedness is held to be such an advantage, do many humans, like the bedouin, cover their skins with wrappings of loose cloth in strong sunlight? Hair protects the skin from direct solar radiation and it also acts as an insulator, by trapping air, keeping its owner warm on cold savannah nights. Hairless humans have to use warm blankets at night to substitute for their ineffective hair. It is strange for any creature of the savannah to be bald unless they have thick skin like the elephant or the rhinoceros.
Other savannah theorists sidestep this reasoning, accepting that nakedness was disadvantageous but arguing that neoteny nonetheless effected the change because the advantages outweighed the disadvantages. The foetuses of great apes are, at one stage of their development, naked. A trigger is needed for neoteny to have occurred but it was not entering the water—it was to accommodate the human learning experience. Maturity was delayed so that an extended childhood could fill the growing brain with knowledge and experience. Gestation, childhood and progress to maturity slowed down relative to other primates—childhood features were retained including childhood curiosity which gave humans the incentive to learn late into their lives. The extension of adult life also meant that parents survived long enough to protect and teach their slow maturing offspring. But neoteny cannot choose the good features of the infant to extend into adulthood and leave unchanged the others. The whole gamut of juvenile features have to be carried into adulthood. Though hairlessness was disadvantageous, the package was advantageous overall and was selected by natural selection.
But this whole notion is easily disproved, first by the success of other primates successfully stepping on to the grasslands at the same time without recourse to neotenous changes, and second by the lanugo of human babies which is overlooked by the savannah theorists. The lanugo is the hairy covering that human foetuses have before birth. They start to become hairy but the hair regresses, and by birth has usually gone, though, on occasions it is retained for a while after birth, to the horror of some parents. The neotenous changes envisaged by the savannah theorists would surely have favored selection of the lanugo to continue into adult life to protect the hominid’s sunboiled skin and retain warmth in the cool nights. We should quickly have been no longer the naked ape. The failure of the lanugo to evolve as a protection shows that human nakedness evolved as a positive response to some situation. Living in water was it.
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- More Adaptations to Water Curious features of Homo sapiens that other apes lack can...
- Where and When was the Human Aquatic Period Where and when did the ape become aquatic?...
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