Clerestory

On Juvenescence

June 16, 2020

Neoteny, or juvenilization, is the delaying or slowing of the development of an animal. It is, at a cellular or physiological level, the act of staying young.

The 100-Year Life argues that the same thing is happening at a behavioural level, and calls the phenomenon “juvenescence.” Though the book is rather short on answers, at least for the people most likely to live to one hundred, its treatment of this aspect of the question of longevity is worth citing:

With this decoupling of age and stage, we will see characteristics previously associated with a specific age becoming more widespread. In particular the multi-stage life requires all ages to retain features previously associated with the young: youthfulness and plasticity; playfulness and improvisation; and the capacity to support novel action taking.

There are some obvious connections here to what I’ve written about serotonin, as well as the avant-garde and selection filters. Serotonin is higher in children, and may increase plasticity in adults. It seems probable that it is involved in creative/exploratory thinking.1

The book’s authors credit Robert Pogue Harrison with the original observation of this phenomenon, and continue:

This youthfulness in part reflects the elongation of adolescence. Humans are unique in the length of time they are socially and economically dependent. The evolutionary advantage of an elongated juvenile stage is the fact that there is more time for education, ensuring that the adult is operating on the basis of learning from past generations rather than simply instinctively. It makes sense with a longer life to further increase this investment in education. Adolescence is a time of flexibility – a time for discovering options and keeping them open rather than making commitments. With the lengthening of life, options become more valuable and so the period over which we explore and create options also lengthens.

Take a look back to the pictures of 16- and 17-year-olds from your grandparents’ generation. In these pictures you will see serious faces that look full of life experiences and dressed in a way indistinguishable from their parents. Now look at pictures from the mid-1950s and already people of the same age are looking and dressing in a more youthful manner. Their style marks the emergence of the teenager – a new social phenomenon of that time. Now look at current photos of people in their 20s and 30s. A similar phenomenon is occurring – but at a different age. These people have the same youthful experience and responsibility-free look of those 1950s teenagers.

In other words, the book argues, people are postponing milestones and look younger even as they get older. Adolescence is elongated, meaning that people are both dependent for longer and educated for longer.

I suspect that the point of this longer education is not, as the authors argue, to improve our knowledge of past learning. It unlikely that we have a better knowledge of history (or have accumulated more general knowledge) than we had in the past — though maybe I’ll think more about this point. Instead, I agree with them about plasticity, and I think that’s what is elongating is the ability to learn itself. I’ve written about this idea in the context of scientific progress.

It also seems to me that rather than a constant trend, as this book observes, it could be the case that society’s attitude towards youth is cyclical.


  1. Could higher serotonin levels (therefore higher entropy) be a mechanism for “juvenescence?” (On the other hand, Carhart-Harris has argued that we’re currently in a lower entropy state than previously, a kind of advanced depression as a species.)


I'm Bryan Kam. I'm thinking about complexity and selfhood. Please sign up to my newsletter or see more here.