...the concept of \"neoteny\"—the retention of juvenile features into adult life. It is a commonplace of human evolution that the transition from Australopithecus to Homo and from Homo habilis to Homo erectus and thence to Homo sapiens all involved prolonging and slowing the development of the body so that it still looked like a baby when it was already mature. The relatively large brain case and small jaw, the slender limbs, the hairless skin, the unrotated big toe, the thin bones, even the external female genitalia—we look like baby apes.

The skull of a baby chimpanzee looks much more like the skull of an adult human being than either the skull of an adult chimpanzee or the skull of a baby human being. Turning an apeman into a man was a simple matter of changing the genes that affect the rate of development of adult characters, so that by the time we stop growing and start breeding, we still look rather like a baby. \"Man is born and remains more immature and for a longer period than any other animal,\" wrote Ashley Montagu in 1961.

The evidence for neoteny is extensive. Human teeth erupt through the jaw in a set order: the first molar at the age of six, compared with three for a chimp. This pattern is a good indication of all sorts of other things because the teeth must come at just the right moment relative to the growth of the jaw. Holly Smith, an anthropologist at the University of Michigan, found in twenty-one species of primate a close correlation between the age at which the first molar erupted and body weight, length of gestation, age at weaning, birth interval, sexual maturity, life span, and especially brain size. Because she knew the brain size of fossil hominids, she was able to predict that Lucy would have erupted her first molar at three and lived to forty, much like chimpanzees, whereas the average Homo erectus would have erupted his at nearly five and lived to fifty-two.

Adult humans look like baby chimpanzees

The boy-genius can be seen as a specific instance of psychological neoteny which is apparently adaptive in modernizing cultures, and it occurred early in science because science is one of the most ‘modern’ and advanced social systems [2]. ‘Neoteny’ refers to the biological phenomenon whereby development is delayed such that juvenile characteristics are retained into maturity. It represents a relatively fast and simple way of evolving adaptations – for instance modern humans in Western Europe have evolved the ability for adults to digest dairy products (which were not a part of the hunter gatherer diet) by the simple method (presumably by a single gene mutation) of neotenously perpetuating the activity of the milk sugar-digesting enzyme lactase from the breast-fed infant throughout mature life.

Probably, the main proximate cause of psychological neoteny in modernizing societies is the prolonged duration of formal education – which may be why the boy-genius arose in an American context where mass higher education and extended schooling was first established [5]. So long as a person is in formal education, or is open to the possibility of returning for more formal education, their minds are in a significant sense ‘unfinished’. Perhaps this could be one reason why scientists so often strike other people as ‘immature’ in their manners and behaviour? Scientists need to be somewhat child-like in order to keep learning and developing. As mass higher education becomes a feature of all liberal democracies, and as the average number of years spent in formal education progressively increases [6], we may expect to accumulate ever-more chronologically middle-aged and elderly people who remain youthfully-minded.

Since modern cultures favour cognitive flexibility, such people tend to thrive and succeed and now set the tone of contemporary life. The biggest praise that can be given to an elderly person is that they have retained the characteristics of youth – not just a youthful appearance, but also the youthful vitality and drive. The modern exemplary geriatric should continue to compete for high status, remain actively interested in love and sex, show themselves adaptive to change, and continually seek new experiences and challenges. Because such attributes are highly valued, they seem to have become much more common.

But of course there is a downside to psychological neoteny, in that the faults of youth are retained as well as its virtues. Modern society is characterized by a short attention span, frenetic sensation- and novelty-seeking, ever-shorter cycles of arbitrary fashion, and (so cultural intellectuals would argue) a pervasive emotional and spiritual shallowness. There are a lot of divorces and broken families. Modern people – it seems fair to say – also lack a profundity of character which seemed commoner in the past. The personality difference between Einstein and Feynman shows this clearly: Einstein had a mature and harmonious personality of great wisdom [7]; while Feynman was vital, protean, witty and life-enhancing - but he was certainly not a sage, and was quicksilver-clever rather than deeply wise [8].

I would expect that this trend to maintain flexible immaturity through adulthood will continue. Psychological neoteny will be matched by perpetuation of youthful appearance: partly natural due to improved health and social conditions, and partly artificial due to continued advance in cosmetic technologies. In future, the most successfully adapted humans may become something like the axolotl – a cave-dwelling salamander which retains its larval form through sexual maturity and until death.

Perpetual education and change has pushed humans into a perpetual state of youthful cognition. Our brains remain childlike in order to continue to learn and adapt to our ever-changing modern environment.