It might just be a product of the turnover of people with whom I have much professional contact, but I’ve not heard as much about human enhancement in the past couple of years as I had in, say, 2010.  In particular, there seems to be less being said about radical life extension.  Remember Aubrey de Grey and his “seven deadly things“?  The idea there was that senescence was attributable to seven basic processes; those basic processes are all perfectly scrutable and comprehensible biological mechanisms.  Therefore, the argument went, if we just put the time and effort into finding a way to slow, halt, or reverse them, we could slow, halt, or reverse aging.  Bingo.  Preventing senescence would also ensure maximum robustness, so accidents and illnesses would be less likely to kill us.  To all intents and purposes, we’d be immortal.  Some enterprising people of an actuarial mindset even had a go at predicting how long an immortal life would be.  Eventually, you’ll be hit by a bus.  But you might have centuries of life to live before that.

Dead easy.

I was always a bit suspicious of that.  The idea that death provides meaning to life is utterly unconvincing; but the idea that more life is always a good thing is unconvincing, too.  What are you going to do with it?  In essence, it’s one thing to feel miffed that one isn’t going to have the time and ability to do all the things that one wants to do: life is a necessary criterion for any good.  But that doesn’t mean that more life is worth having in its own right.  Centuries spent staring at a blank wall isn’t made any better by dint of being alive.

But a letter published this week in Nature suggests that there is an upper end to human lifespan after all.  In essence, the demographic data seem to suggest that there’s an upper limit to survivability.  That being the case, we should stop worrying about making people live longer and longer, and concentrate on what’s going on during the 125 years or so that Dong, Milholland and Vijg think is allotted to us.

Others reject the claim.  According to the BBC, James Vaupel of the Max Planck Institute has apparently labelled the study a “dismal travesty”, which is a gloriously intemperate thing to say.  But it is true that the work reported in the letter is empirical, and so tells us little about what is possible in principle.  It may be that we’re reaching the upper limits of how long people can expect to live given prevailing conditions – but there may be a huge shift in our modes of life in a generation or so that’ll make what we take to be inevitable now not inevitable, and our acquiescence to it may come to appear naïve.  Indeed, Dong, Milholand and Vijg get close to admitting that they don’t know why their hypothesised upper limit is where it is:

What could be the biological causes of this limit to human lifespan?  The idea that ageing is a purposeful, programmed series of events that evolved under the direct force of natural selection to cause death has now been all but discredited.  Instead, what appears to be a “natural limit” is an inadvertent byproduct of fixed genetic programs for early life events, such as development, growth and reproduction.  Limits to the duration of life could well be determined by a set of species-specific, longevity- assurance systems encoded in the genome that counteract these inadvertent byproducts, which are likely to include inherent imperfections in transferring genetic information into cellular function.

This reminds me of a book I was reading about a year ago: Nick Lane’s The Vital Question.  The wet sciences have never been my happy place, and I fear that a lot of Lane’s argument went over my head – but one of the take-home messages there is that there are good reasons based in biophysics to think that there’s a natural upper limit to human lifespan.  And that upper limit is… around 120 years, give or take.

It’s strikingly close to the empirical work in Nature.

Now, of course, we could respond that if this time limit is written in the cell, it doesn’t follow that we have to be bound by it.  We could imagine a world in which we discover how to manipulate the biophysics in such a way as to increase life expectancy by an order of magnitude.  If dying is bad, or if preventing a death is the same as saving a life and we have a duty to save lives where possible, then we could generate an argument for researching that kind of manipulation.  Lots of people have already gone down that route.  But, all the same, there’s still the question of whether it’s worth it.  I’m not convinced that it really is.

What, really, would be the point?  Don’t we have much better things to do with our lives than to worry about their duration?

I don’t have the space here to provide a detailed argument about why.  But try this as a stopgap.  There’s a ton of videos on YouTube from the annual Cooper’s Hill cheese-rolling thingy.  Inevitably, there’re images of people shuffling slowly down the hill, filming themselves as they do so.  This is absurd.  They’re putting so much into recording their participation in the event that they aren’t actually participating in it at all – which means that their record is meaningless.  People who maunder on about extending life-expectancy strike me as doing the same thing.  I think that Nick Agar makes a similar point in Humanity’s End.

It may be that it’s the way we run society that makes it hard to break the 120-year barrier; it may be biology.  Both those things are changeable.  I don’t know which is the harder to change.  But… Well, speaking as someone just entering middle age, 120 years seems more than enough, no?