In the far future of my space opera setting I write my stories in, about a thousand years into the future, genetic engineering has advanced, and the human mainstream has embraced its power, making themselves (by our standards) very beautiful, very intelligent, and, most importantly, ageless. There’s a reason why I always keep the exact age of my far-future characters very vague in my far-future stories: because I’m somewhat uncertain what the exact life cycle would look like!
Averting Geriatric Stagnation
As I touch upon in my post “Worldbuilding Immortals in Science Fiction”, one deleterious potential effect of agelessness is in drastically raising the average age; given youth-American mortality rates the population’s half-life is 858 years, so given a stable population that would be the median age. Old people tend to be much more stuck in their ways and risk-averse than young people. Brian Hoover over at Paladium, in a somewhat different context, presumes, reasonably in my view, that the natural cycle from aggressive youth to complacent midlife to conservative senility is mediated by hormones, and that old men made hormonally young will avoid elderhood’s deleterious effects.
However, I’d speculate that the most insidious effects of old age, namely rigidity and becoming stuck in your ways, are direct consequences of more life experience, and cannot be cheated by making the body more youthful. What’s really needed, therefore, is a more plastic and youthful brain, if a superficially-youthful geriatric stagnation is to be avoided. What exactly would this look like?
The Orion’s Arm worldbuilding project for their part speculate that this could be genetically engineered, and that humans could retain the flexibility and sponge-like nature of the youthful brain indefinitely, but at the cost of this more plastic brain being much more forgetful. Not being stuck in your ways implies forgetting your ways and constantly renewing yourself, potentially with aspects of your personality changing along the way (not too much in my view, as the vast majority of your personality is innate, but the part that’s down to environment or choice would shift, exerting some significant effect).
Not aging yet also forgetting most of your experiences by the time something or another falls you isn’t necessarily all that appealing, but it’s possible that the memories wouldn’t be truly forgotten, just blended into a haze, with only the strongest memories standing out vividly. A version of this already happens in old age as it is, so accentuating it shouldn’t be too hard.
It might also be possible to compartmentalize these memories and suppress them, isolating their effect from the mind more broadly but with them all still being accessible with deliberate effort. Something like this can be done today with hypnosis, but it’s an extremely weak tool, woefully incapable of the full-blown version. Making such a process an inborn faculty of the brain would seem a sounder approach, but that level of genetic or even spiritual engineering seems a bit too advanced for my setting in the 4th millennium, but should be feasible in later eras.
Another much more out-there possibility is to cycle between childhood and adulthood; let’s say every century a youthful-presenting human, rather than dying, instead regenerates into a small child, beginning the cycle anew. That might seem crazy, but Turritopsis dohrnii, the so-called immortal jellyfish, does this already! If such an ability exists in nature it can likely be engineered into man given enough time and effort.
I’m thinking different races of man might pursue each avenue. Some letting the elders get set in their ways, some letting them forget everything, some taking a more in-between approach, and some imposing a regeneration cycle.
In any case, in my far future if you see someone who looks 20 they might actually be 20, or they might easily be 200. It’s hinted at several points in my stories that some young-looking people aren’t as young as they might seem, with many possessing an aura of wisdom, serenity, and experience that can only be accumulated with old age. One never knows for sure, though, how old they are.
The smarter the Race, the longer the Childhood
That goes even for the 20-year-olds! The primary reason I’m vague about people’s ages is that I’m unsure what the effects of greatly enhanced intelligence would be. Steven Hsu speculates that if all the gene variants that raise intelligence were engineered into one man he would be 100 standard deviations above average, i.e. an IQ of over 1000. For comparison, IQ tops out at around 200 now. That’s a big difference.
The rule among animal species is the more intelligent species spend a longer time in childhood, because that sponge-like brain needs more time to develop and to absorb the world and everything there is to know about it. As Marco DelGiudice writes in the Handbook of Life Course Health Development:
In biological terms, middle childhood corresponds to human juvenility —a stage in which the individual is still sexually immature, but no longer dependent on parents for survival. In social mammals and primates, juvenility is a phase of intense learning—often accomplished through play—in which youngsters practice adult behavioral patterns and acquire essential social and foraging skills. Indeed, the duration of juvenility in primates correlates strongly with the size and complexity of social groups, as well as with cortical brain volume (Joffe 1997). Social learning in juvenility can be understood as investment in embodied capital—skills and knowledge that cost time and effort to acquire but increase an individual’s performance and reproductive success (Kaplan et al. 2000).
As a rule, the smarter the species, the longer the juvenility, which is why middle childhood lasts as long in humans as all of early childhood put together. Given a far smarter human race, it stands to reason juvenility might need to be correspondingly lengthened.
How much longer would childhood need to be? There doesn’t seem to be that noticeable a difference between the smartest and dumbest humans today, but that’s at most 10 standard deviations, not 100, so who knows? It might be the case that more middle childhood is optimal even if smarter humans don’t get it naturally. As a very rough guess I’d say maybe 2 to 3 times the length spent in middle childhood today (with correspondingly slower growth rates after age 7 or so) might be optimal. This implies that rather than maturing at 13 humans would instead mature at 20 or 27.
On the other hand, who’s to say such an extended middle childhood is actually necessary if you have genetic engineering available and could use techniques nature passed by? For all we know the whole human growth cycle could be greatly compressed with little or no ill effects. So you could have children that mature much faster as opposed to slower!
And of course there’s always the possibility that you could engineer in much faster or slower growth for other reasons, or the same rate of growth we have today because it’s more natural and ancestral, and accept whatever trade-offs, if any, that result from those choices.
The net effect is I’m not really sure how old exactly the youngest adults would be in such a setting, but I am reasonably sure that the early-childhood life cycle would be similar, hence why babies and small children are depicted as growing about the rate they do today.
It might be the coolest option to just say that all these options are viable, both for the growth rates and for the stodgy-immortals problem, and that different races make different choices, just accepting different trade-offs. I think I’ll go with that…