In case anyone was curious like me: the standard deviation of lifespan is ~12-15 years in developed countries.
So environmental effects, sleep, diet, lifestyle, etc (I.e. modifiable factors) maybe account for half of that, so like 6-7.5 years of variance. Which… sounds about right to me.
Lifespan is not even half the story though, health span is much more important. Your life is completely different if you can ski or split your own wood at 80+ vs being barely able to use stairs at 50. Both might die at 90 but one "lived" 30 years more
It is probably more than half the story. Health span is strongly correlated to life span, although not completely. The median "health span gap" is about 10 years, and has widened by roughly one year over the past 20 years. However, this is probably just due to an aging population and not necessarily from any factors you can control fully.
I wouldn't be surprised if "health span" (although defining it is difficult) exactly mirrors the inheritability pattern of mortality.
It depends on the definition, if you're even just 20kg overweight you're living a wildly different life than you'd have if you were fit, you're closing so many doors by default and making a bunch of things much harder than they should be, But you're still considered "healthy" here
Yeah, been working in IT since forever (sitting work all day), but started lifting recently and it already made remarkable improvements in my wellbeing. Should've started sooner of course, but I'm still well in time.
One of the most consistent health research findings Ive heard in recent years is the benefits of weight training for older adults. Hopefully the message is being received.
Too many people think your life is a binary 'living or dead' when thats not the case at all. I didn't even understand it fully till I was hit by a car.
This is a nice example/re-stating of what the heritability % "means" here.
I'm curious, with something like smoking/drinking, how you can be confident that you've untangled genetic predispositions to addiction or overconsumption from those "modifiable factors". I guess that's just captured within the 50% heritability? And if you could confidently untangle them, you might find heritability is higher than 50%?
Heritability is a pretty funky concept because it's contextual to a certain point in time, environment, and population, effectively.
An example I like is that if you measured the heritability of depression in 2015, and then you measured the heritability of depression in 2021, you would likely see changes due to environmental effects (namely, there's the pandemic/lockdowns and this could conceivably cause more people to experience depressive symptoms). Let's assume we make those measurements and the rate of depression did increase, and we could tie it causally to the pandemic or related events.
In that scenario, the heritability of depression would have decreased. I don't think anyone would argue there were massive genetic changes in that 6 year time period on a population scale, but the environment changed in a way that affected the population as a whole, so the proportion of the effect on the trait which is genetically explained decreased.
For something like lifespan in the above example, you can imagine that in a period of wartime, famine, or widespread disease the heritability would also decrease in many scenarios (if random chance is ending a lot of lives early, how long the tail of lifespan is influenced genetically is much less important).
Given that note, it's generally tricky to talk about whether heritability increases or decreases, but with more accurate estimates of how genetic predispositions form you could see the heritability of certain traits increase with the environment held stable, as there's certainly ones that may be underestimated or genetic factors that aren't currently accounted for in many traits.
*edit: I realized I never mentioned the other thing I wanted to mention writing this! since you mentioned what the percent heritability means here, I think the best way to think of it is just "the proportion of phenotypic variation for this trait in a measured population which is explained by genetic variation." So it's dependent on the amount of variation in several aspects (environmental, genetic, phenotypic).
> the standard deviation of lifespan is ~12-15 years in developed countries.
That seems rather higher than I would have expected, at least if one corrects for preventable accidents and other such things (that I would expect to shift the results away from a normal distribution).
Lifespan isn't as important as healthy lifespan. Lifestyle can mean the difference between being able to complete an Ironman triathlon at age 80 vs being bedbound.
Keep in mind this research is based on correcting twin study heritability estimates for confounding effects. However, new research shows that heritability estimates derived from twin studies are themselves dramatically inflated: https://open.substack.com/pub/theinfinitesimal/p/the-missing...
How is heritabiltity of life span useful if by the time the lifespan becomes known (eg at 80yrs old) the inheritance is not possible anymore (eg menopause)?
Heritability acts on lineages, not individuals (in general, not always) - a good rule of thumb is that traits that benefit 3 or more generations of a family have a good shot at being propagated. In this case, the advantage (of both menopause and longevity) is increased well-being of the tribe, ampliyfing the positive effects of culture and stability. Wisdom of the elders is implicit to the genetics. This is a tradeoff with the cost in resources; at some point the cost to keep someone around might exceed the benefit, but from an evolutionary standpoint, the accounting is over a lifetime; in a relatively stable environment, genes that improve longevity and healthspan will be reinforced by the positive feedback loops of culture and nurture and civilization and technology. Menopause is also prevalent in orcas and a handful of other mammals - and older females help rearing and protecting babies, and so forth, with a protoculture providing that feedback loop.
In (quantitative) genetics literature, heritability is usually defined (simplifying a bit) as the proportion of variance of a trait (lifespan, height, etc), in a population, that can be explained by genetics. The rest, by environmental factors, or error.
If height were a 100% heritability means that all differences in height between individuals would be explainable by genetics.
Note that evolution isn't about individuals, it's about genes (which we should further note is more than just DNA, but that's a different discussion). If it weren't valuable for humans to live at all without being fertile, then the average age of menopause and the average age of death would likely be much closer together. As it turns out, the human genes that were best able to pass themselves along were those that kept old people around despite being infertile, presumably to the benefit of helping to raise grandchildren, among other things.
Healthy grandparents that are around to support their children and take care of grandchildren increase the fitness of the entire lineage by helping their children have more children and those grandchildren to be healthier/safer.
If you are interacting with a carrier of your genes at all while they still might reproduce, you are having an impact on their fitness and thus evolutionary pressure exists.
Given the opportunity, one wonders what you'd like to do with 'old people consuming resources without adding anything and supposedly 'holding back societies'. Earlier in the 20th century a significant cohort of intellectuals had decided ideas on this and the earlier generations.
Related somewhat to this: 'The Intellectuals and the Masses' by John Carey makes for truly shocking reading.
Those old people used to be young and helped pay for their parents and grandparents to live into old age. Part of being young and productive is helping take care of those less able than you, including the elderly.
Unless you're volunteering to work for 40 years then be executed on retirement, I think you should delete that comment and that thought from your mind.
This finding rectified my mental model of longevity after a long, perplexing period where longevity was estimated to be much less heritable than expected when comparing to other studied traits.
Yes but those aren’t random samples. Children not raised with their birth parents had different circumstances. As did children who got split up, and families adopting children is also a selection bias.
In case anyone was curious like me: the standard deviation of lifespan is ~12-15 years in developed countries.
So environmental effects, sleep, diet, lifestyle, etc (I.e. modifiable factors) maybe account for half of that, so like 6-7.5 years of variance. Which… sounds about right to me.
Lifespan is not even half the story though, health span is much more important. Your life is completely different if you can ski or split your own wood at 80+ vs being barely able to use stairs at 50. Both might die at 90 but one "lived" 30 years more
It is probably more than half the story. Health span is strongly correlated to life span, although not completely. The median "health span gap" is about 10 years, and has widened by roughly one year over the past 20 years. However, this is probably just due to an aging population and not necessarily from any factors you can control fully.
I wouldn't be surprised if "health span" (although defining it is difficult) exactly mirrors the inheritability pattern of mortality.
> The median "health span gap" is about 10 years
It depends on the definition, if you're even just 20kg overweight you're living a wildly different life than you'd have if you were fit, you're closing so many doors by default and making a bunch of things much harder than they should be, But you're still considered "healthy" here
Yeah, been working in IT since forever (sitting work all day), but started lifting recently and it already made remarkable improvements in my wellbeing. Should've started sooner of course, but I'm still well in time.
Lot of people think it's a niche exercise activity and it shouldn't be - for all ages including those in their 80s and 90s according to reports.
One of the most consistent health research findings Ive heard in recent years is the benefits of weight training for older adults. Hopefully the message is being received.
It's a remarkable tragedy how many people don't understand your point.
https://en.wikipedia.org/wiki/Disability-adjusted_life_year
Too many people think your life is a binary 'living or dead' when thats not the case at all. I didn't even understand it fully till I was hit by a car.
As many of the health nutters say, the goal is "live well, drop dead."
One note: the standard deviation of the remaining effects would be sqrt(1/2) as large, not 1/2 as large. So more like 8.5-10.5 years.
This is a nice example/re-stating of what the heritability % "means" here.
I'm curious, with something like smoking/drinking, how you can be confident that you've untangled genetic predispositions to addiction or overconsumption from those "modifiable factors". I guess that's just captured within the 50% heritability? And if you could confidently untangle them, you might find heritability is higher than 50%?
Heritability is a pretty funky concept because it's contextual to a certain point in time, environment, and population, effectively.
An example I like is that if you measured the heritability of depression in 2015, and then you measured the heritability of depression in 2021, you would likely see changes due to environmental effects (namely, there's the pandemic/lockdowns and this could conceivably cause more people to experience depressive symptoms). Let's assume we make those measurements and the rate of depression did increase, and we could tie it causally to the pandemic or related events.
In that scenario, the heritability of depression would have decreased. I don't think anyone would argue there were massive genetic changes in that 6 year time period on a population scale, but the environment changed in a way that affected the population as a whole, so the proportion of the effect on the trait which is genetically explained decreased.
For something like lifespan in the above example, you can imagine that in a period of wartime, famine, or widespread disease the heritability would also decrease in many scenarios (if random chance is ending a lot of lives early, how long the tail of lifespan is influenced genetically is much less important).
Given that note, it's generally tricky to talk about whether heritability increases or decreases, but with more accurate estimates of how genetic predispositions form you could see the heritability of certain traits increase with the environment held stable, as there's certainly ones that may be underestimated or genetic factors that aren't currently accounted for in many traits.
*edit: I realized I never mentioned the other thing I wanted to mention writing this! since you mentioned what the percent heritability means here, I think the best way to think of it is just "the proportion of phenotypic variation for this trait in a measured population which is explained by genetic variation." So it's dependent on the amount of variation in several aspects (environmental, genetic, phenotypic).
> the standard deviation of lifespan is ~12-15 years in developed countries.
That seems rather higher than I would have expected, at least if one corrects for preventable accidents and other such things (that I would expect to shift the results away from a normal distribution).
Lifespan isn't as important as healthy lifespan. Lifestyle can mean the difference between being able to complete an Ironman triathlon at age 80 vs being bedbound.
Keep in mind this research is based on correcting twin study heritability estimates for confounding effects. However, new research shows that heritability estimates derived from twin studies are themselves dramatically inflated: https://open.substack.com/pub/theinfinitesimal/p/the-missing...
How is heritabiltity of life span useful if by the time the lifespan becomes known (eg at 80yrs old) the inheritance is not possible anymore (eg menopause)?
Heritability acts on lineages, not individuals (in general, not always) - a good rule of thumb is that traits that benefit 3 or more generations of a family have a good shot at being propagated. In this case, the advantage (of both menopause and longevity) is increased well-being of the tribe, ampliyfing the positive effects of culture and stability. Wisdom of the elders is implicit to the genetics. This is a tradeoff with the cost in resources; at some point the cost to keep someone around might exceed the benefit, but from an evolutionary standpoint, the accounting is over a lifetime; in a relatively stable environment, genes that improve longevity and healthspan will be reinforced by the positive feedback loops of culture and nurture and civilization and technology. Menopause is also prevalent in orcas and a handful of other mammals - and older females help rearing and protecting babies, and so forth, with a protoculture providing that feedback loop.
In (quantitative) genetics literature, heritability is usually defined (simplifying a bit) as the proportion of variance of a trait (lifespan, height, etc), in a population, that can be explained by genetics. The rest, by environmental factors, or error.
If height were a 100% heritability means that all differences in height between individuals would be explainable by genetics.
Note that evolution isn't about individuals, it's about genes (which we should further note is more than just DNA, but that's a different discussion). If it weren't valuable for humans to live at all without being fertile, then the average age of menopause and the average age of death would likely be much closer together. As it turns out, the human genes that were best able to pass themselves along were those that kept old people around despite being infertile, presumably to the benefit of helping to raise grandchildren, among other things.
Explanation I've heard in popscience books:
Healthy grandparents that are around to support their children and take care of grandchildren increase the fitness of the entire lineage by helping their children have more children and those grandchildren to be healthier/safer.
You can make it broader and simplify:
If you are interacting with a carrier of your genes at all while they still might reproduce, you are having an impact on their fitness and thus evolutionary pressure exists.
What is the question you are asking? What does "useful" mean, in other words? How does it contribute to the reproductive success of the offspring?
It's probably not that useful beyond some age. Old people consuming resources without adding anything or holding back societies.
Given the opportunity, one wonders what you'd like to do with 'old people consuming resources without adding anything and supposedly 'holding back societies'. Earlier in the 20th century a significant cohort of intellectuals had decided ideas on this and the earlier generations.
Related somewhat to this: 'The Intellectuals and the Masses' by John Carey makes for truly shocking reading.
Who? https://www.theguardian.com/books/2025/dec/14/john-carey-obi...
Those old people used to be young and helped pay for their parents and grandparents to live into old age. Part of being young and productive is helping take care of those less able than you, including the elderly.
Unless you're volunteering to work for 40 years then be executed on retirement, I think you should delete that comment and that thought from your mind.
the more little old ladies around, the easier it is to raise kids.
This finding rectified my mental model of longevity after a long, perplexing period where longevity was estimated to be much less heritable than expected when comparing to other studied traits.
There's also some wisdom in that if you make kids later in life, you pass them the genes to survive (with 50% probability it seems) up to that age.
So if you're in the kind of family that dies of cancer at 30, and make kids at 25, perspectives don't look great.
Wait. They studied twins, removed accidents etc. But wouldn’t this lead to overestimation of heritability due to shared environment?
FTA: “We use mathematical modeling and analyses of twin cohorts raised together and apart”
So, take one cohort of twins raised together and see how well their life spans correlate.
Take another cohort of twins separated at or near birth and do the same.
Then, do some math magic with both to estimate heritability.
The obvious problem you run into with twins raised apart is that there in fact aren't many twins who are raised apart.
Yes but those aren’t random samples. Children not raised with their birth parents had different circumstances. As did children who got split up, and families adopting children is also a selection bias.
Yeah I’d take this study with a spoon of salt. As with many human studies, it’s hard to control for all factors.
Seemingly due to reduction in extrinsic factors affecting lifespan.
Rats. I have ancestors that died at 97, others at 81. Some even younger. So, no telling.
do you know what they died of? car accidents are probably less heritable, unless they're caused by heritable rash behaviour...
Cancer mostly. Except Mom. She died of heart failure at 97. That's mostly, tired of living so long. She gave up.
tangentially, readers may be interested in this paper: https://stateofutopia.com/papers/1/evolving-brains-cull-long...
(you can reproduce its results yourself in a few minutes).
Shorter lifespans drive faster evolution. That was taught in basic biology and we, as a society, know it all too well (infectious diseases).
It’s difficult to square obsession with a long life with a healthy humanity.