The axolotl is a peculiar amphibian: it never undergoes metamorphosis, retaining its gills and living in water through its entire life, a kind of tadpole with feet.
Studying the axolotl in the late 19th century, the German zoologist Julius Kollmann coined the term “neoteny” to describe this process—the retention of youthful traits into adulthood.
Neoteny has gone on to have a provocative history within biology. Evolutionary biologists throughout the twentieth century, including Stephen Jay Gould, discussed and debated neoteny as one of the mechanisms of evolution and one of the distinguishing features of Homo sapiens in particular. Compared to our fellow primates, we mature later, more slowly, and somewhat incompletely: we stay relatively hairless, with larger heads, flatter faces, bigger eyes. Human adults, that is, strongly resemble chimpanzee infants.
(Intriguingly, our typical depiction of an even more highly evolved species than ourselves—namely, aliens—is one of enormous heads, huge eyes, tiny noses: namely, a species even more neotenous than we are.)
Neoteny, depending on how far one wishes to extend the term beyond considerations of pure anatomy, also functions as a description of human cognitive development and human culture. A baby gazelle can outrun a predatory cheetah within several hours of being born. Humans don’t even learn to crawl for six months. We’re not cognitively mature (or allowed to operate heavy machinery) for decades.
Indeed, humans are, at the start of our lives, among the most uniquely useless creatures in the entire animal kingdom. Paradoxically this may be part and parcel of the dominant position we hold today—via the so-called Baldwin effect, where we blend adaptation by genetic mutation with adaptation by learning. We are, in effect, tuning ourselves to our environment in software, rather than in hardware. The upside is we can much more rapidly adapt (including genetically) to selective pressures. The downside: longer childhoods.
Human culture itself appears to progress by way of neoteny. Thirteen-year-olds used to be full-fledged adults, working the fields or joining the hunting parties. Now we grouse that “grad school is the new college,” our careers beginning ever later, after ever-lengthening periods of study and specialization.
Computer scientists speak of the “explore/exploit” tradeoff—between spending your energy experimenting with new possibilities and spending it on the surest bets you’ve found to date. One of the critical results in this area is that in problems of this type, few things matter so much as where you find yourself on the interval of time available to you.
The odds of making a great new discovery are highest the greener you are—and the value of a great discovery is highest when you’ve got the most time to savor it. Conversely, the value of playing to your strengths, going with the sure thing, only goes up over time, both as a function of your experience and as a function of time growing scarce. This naturally puts all of us, then, on an inevitable trajectory: from play to excellence, from craving novelty to preferring what we know and love. The decision-making of the young—whether it’s who to spend time with, where to eat, or how to work and play—really should differ from the decision-making of the old.
And yet even here there is an argument to be made for neoteny, of a kind of conscious and deliberate sort.
To imagine ourselves as making choices not only on our own behalf, but on behalf of our peers, successors, and descendants, is to place ourselves much more squarely at the beginning of the interval, an interval much vaster than our lifetime. The longer a future we feel ourselves to be stewarding, the more we place ourselves in the youth of the race.
This offers something of a virtuous circle. A host of results in neuroscience and psychology show that the brain appears to mark time by measuring novel events in particular. “Life is long,” we think, and the effort of exploration is worthwhile. In turn, the explorer is immune to the feeling of time speeding up as they age. The mindset is self-fulfilling. To lengthen youthfulness is to lengthen life itself.