Scientists find humans age dramatically in two bursts – at 44, then 60 | Hacker News Reader

Scientists find humans age dramatically in two bursts – at 44, then 60

theguardian.com

77 pointsnemoniac11 comments

This lines up quite well with the late-acting error theory of aging. This theory basically states that many mutations have some kind of clock associated with them, ie they are more likely to cause negative effects after some period of time. There is a lot of evolutionary selective pressure to weed out such mutations that trigger when we are young as those impede reproduction. However as we get older, there is less selective pressure, particularly in pre-industrial times. There is still some selective pressure, as living parents and grandparents help raise and provide resources for later generations even after they stop reproducing, but it diminishes.

So a mutation that causes heart attacks in your twenties is obviously going to die out, but a mutation that causes heart attacks in your 50s could survive. If you had a mutation that would guarantee a heart attack in your 130s, you would never know, nor would evolution; but as the odds of living to an advanced age increase, so too do the odds of experiencing the negative effects of these late-acting mutations.

If this theory is correct, we should not see a perfectly smooth increase in age-related effects, instead we should see spikes near significant life milestones. Assuming a generation length of about 20 years, these peaks correspond reasonably well to the points where grandchildren would be able to take care of themselves, and the point where those grandchildren start having kids of their own. The rate of change of your biomolecules is the derivative of the selective pressure. So basically there is strong selective pressure to live long enough to help with the early days of raising your grandkids, then pressure suddenly drops to an intermediate level - a grandparent is about as helpful to a 8 year old as a 14 year old - then by the time you're a great-grandparent your progeny is setup as good as its ever going to be, and selective pressure drops further.

While I am sure there are ways of explaining these peaks with other theories of aging, like lifestyle changes at the ages increasing the rate of accumulation of damage, it seems to me such explanations would not be resilient across genders and especially not across cultures or socioeconomic conditions.

> However as we get older, there is less selective pressure, particularly in pre-industrial times.

Note that the industrial revolution did not necessarily significantly expand how long humans live. Most people who made it to adulthood could expect to live a long life, and there was only a small increase in the maximum human age. Rather, most of the difference was a drop in child mortality.

Thus, many of the selective pressures would have remained the same. But the overall point is correct -- evolutionary fitness in older age has less selective pressure than in younger age.

This is not true. While the extremely low life expectancies are indeed mostly a result of high infant mortality, and the maximum life expectancy was comparable, people that reached adulthood still died substantially younger than today.

For example amongst english aristocracy that made it to 21, the average lifespan was early 60s for most of the period from 1200 to 1750. The average age of death of English kings from 1000 to 1600 was 48. Excavations of graves of anglo-saxon field workers from 400-1000 found none over 45, while among clergy only 5% lived past 45. For English commoners from 1200 to 1750, adult life expectancy was generally early 50s.

People did not drop dead due to old age at these younger ages. The odds of dying due to malnourishment or disease were much higher at every age range. It was very possible for someone to live into their 90s back then, it was just substantially rarer.

https://www.statista.com/statistics/1102957/life-expectancy-... https://www.sarahwoodbury.com/life-expectancy-in-the-middle-....

That's a very interesting theory, but in the context of generations couldn't frailty and appearances associated with frailties be advantages that outweigh occasional post reproductive death when too many combine?

If we were more like sharks and grand parents were larger, more intimidating, and almost always able to maintain status via direct physical confrontation, I kind of wonder how grand relationships would look, whether there would be larger chaos in generational changes with longer over shadowed generations, etc.

The figure showing the bursts is at [1], and the Nature article itself is at [2].

All the people in the study lived in California, perhaps near Stanford where many of the authors are. It would be interesting to repeat the exact same process on a completely different cohort, say a South American tribe. Or for that matter, farm workers from California's Central valley.

[1] https://www.nature.com/articles/s43587-024-00692-2/figures/4

[2] https://www.nature.com/articles/s43587-024-00692-2

Why do all those graphs peak at the same ages so clearly?

I am probably missing something, but if this phenomenon is so clearcut in the graphs, how come it took so long to be discovered?

Or for that matter, on all of the above, and any other groups one can think of; and perhaps also a "group of random individuals" study or three.

If this is true, shouldn’t we see small spikes of mortality at those ages?

Observationally and personally true.

honest to goodness, I think this lines up with my experience, at least for men.

Not sure about menopause lol!

Honestly 40 has been pretty rough!

Reply on news.ycombinator.com