>By contrast, intrinsic mortality stems from processes originating within the body, including genetic mutations, age-related diseases, and the decline of physiological function with age

So we put genetic diseases in the bucket of intrinsic mortality and then found that intrinsic mortality has a heritable component?

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.

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...

The 50% number is a bit mysterious, but if I understand the text of the article correctly, it essentially means that if we do not account for the noise added by accidents and such, we get a Pearson correlation of life expectancies of monozygotic twins of ~0.23. If we correct for accidents, the correlation rises to 0.5, hence 50% (with some further analysis they go up to 0.55, hence "above 50%" in the abstract). Now, in practical terms, this means that, given a MZ twin who died recently of natural causes, we could obtain an estimate for ourselves, but only if we make additional assumptions. A correlation coefficient alone is not very informative.

There's a lot of genes that impact lifespan, both good and bad. For example my father has hereditary hemochromatosis due to 2 copies of the HFE C282Y mutation. He was diagnosed in his 50's, so I'd expect the damage it did to his body to impact lifespan.

In my case I don't have it (I'm just a genetic carrier). If I did have the genotype and took the necessary dietary measures to avoid the phenotype, then it likely wouldn't impact lifespan.

On one hand you can argue a heritable disease like HHC has an impact on lifespan, but with genetic testing and treatment you can argue it doesn't impact lifespan (or it's impact is significantly mitigated).

The problem with twin studies:

1. There are genetic mutations that make you immune to HIV.

2. Monozygotic twins will both be immune, or not immune, while dizygotic twins may be either, one can be immune, while the other one could get AIDS.

3. Thus, a twin study would likely show that AIDS is a genetic defect.

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.

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)?

I know enough about heritability to know that the science people use words differently than I expected, but not enough to explain that so here's someone's article about it:

https://dynomight.net/heritable/

Genetics may predispose for nicotine addiction, obesity, alcoholism, etc. This is intended design of genetic studies which look at multiple genes, like twin studies, GWAS studies, etc.

I think the studies which find a single gene variant which would have large impact on lifespan would be interesting. Not sure if variants like that exist though.

It's interesting on my mother's side of the family, most everyone lived well into their 80's and 90's. The execution being for my Mom and her sisters who smoked heavily. Her brothers both died in their 60's but were in the Vietnam war and were definitely exposed to Agent Orange and both had brain cancer. My dad lived until nearly 80 after smoking since he was 12 years old and 2-3 packs per day.

In the absence of other evidence, isn't it the case that any given trait is 50% heritable and 50% environmental?

Rats. I have ancestors that died at 97, others at 81. Some even younger. So, no telling.

Wait. They studied twins, removed accidents etc. But wouldn’t this lead to overestimation of heritability due to shared environment?

Seemingly due to reduction in extrinsic factors affecting lifespan.

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).

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.

Now, not to these people shouldn't make kids but perhaps, choose a spouse whose family dies on average at 60+?

Marry "up", not "down" :)

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