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 almost never reasonable to assume normality and make calculations like this. This is particularly the case when you are dealing with lifespan, which isn't normally-distributed even in the slightest. The actual ranges are likely smaller than you are stating here, and variance is just not a very practical or interpretable metric to use when dealing with such a skewed distribution.

We should be stating something like a probability density interval (i.e. what is the actual range / interval that 95% of age-related deaths occur within), and then re-framing how much genetic variation can explain within that range, or something like it. As it is presented in the headline / takeaway, the heritability estimate is almost impossible to translate into anything properly interpretable.

https://biology.stackexchange.com/questions/87850/why-isnt-l...

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%?

Environmental effects are not necessarily modifiable. It includes randomness, background radiation, unknown risk factors, anything which is not genetic.

> 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.