It seems reasonable to assume that there's a genetic component to aging and the human life span. For example, it's clear that if you inherit bad genes (alleles) from your parents then your chances of living a long life will be diminished. It's also clear that a lot of deaths (short life span) are not due to alleles you inherit from your parents but to extrinsic factors such as accident, war or disease. It's true that some diseases, such as cancer, have a heritable component but even people with "good genes" can die of cancer.
What's not clear is how much of the underlying, intrinsic, component of life span is due to alleles you inherit from your parents. If you look at the average life expectancy of men and women in different countries you can see that the average life expectancy of an American is about 80 years but people in Japan can expect to live five years longer. Is that difference due to genetics, or better health care, or something else?
A recent paper in Science (January, 2026) attempts to answer some of these questions by looking at three sets of twin studies in order to estimate the heritability of life span.
Shenhar, B., Pridham, G., De Oliveira, T.L., Raz, N., Yang, Y., Deelen, J., Hägg, S. and Alon, U. (2026) Heritability of intrinsic human life span is about 50% when confounding factors are addressed. Science 391:504-510. [doi: 10.1126/science.adz1187]
How heritable is human life span? If genetic heritability is high, longevity genes can reveal aging mechanisms and inform medicine and public health. However, current estimates of heritability are low—twin studies show heritability of only 20 to 25%, and recent large pedigree studies suggest it is as low as 6%. Here we show that these estimates are confounded by extrinsic mortality—deaths caused by extrinsic factors such as accidents or infections. We use mathematical modeling and analyses of twin cohorts raised together and apart to correct for this factor, revealing that heritability of human life span due to intrinsic mortality is above 50%. Such high heritability is similar to that of most other complex human traits and to life-span heritability in other species.
The authors note that previous studies on the heritability of life span gave low estimates. The contribution of genes was less than 25% in most studies. This value seems low compared to studies of life span in mice and data on other human traits and the authors speculate that the low value was due to confounding factors such as extrinsic mortality. They also note that deaths due to extrinsic mortality have declined considerably in Western cultures the last 100 years so maybe it's time to revisit the question using more recent deaths.
Most of the analysis relies on complex modeling that's impossible to evaluate unless you're an expert in this sort of thing. They looked at the data from three different twin studies in Sweden and Denmark where there was enough information on cause of death to separate extrinsic and intrinsic effects. The study distinguished between monozygotic and dizygotic twins and compared twins raised together and raised apart. The study only looked at twins born between 1900 and 1935 where both twins survived to age 61.
Figure 2 (below) shows the correlation between the age of death of monozygotic twins where the extrinsic (red) and intrinsic (blue) deaths are separated by the model. It shows that once extrinsic deaths are eliminated there is a strong correlation between the ages of death of the two twins. If one of them dies at age 80 then there's a good chance that the other will die at a similar age.
This data can be used to estimate the heritability of life span and the value calculated by the authors is about 55%. This means that genetics accounts for about 55% of all the factors contributing to life span. If your parents died earlier than the average life span then chances are you will too. If your parents lived into their 90s then it's likely that you will also live to be 90.
The results seem interesting and reasonable but keep in mind that they rely on complex mathematical models that are pretty opaque to most of us. I'm skeptical that peer review is capable of recognizing any flaws in the analysis. We'll have to wait and see if these results can be duplicated and whether other experts agree with the methodology.
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