The Hidden Genetic Blueprint of Longevity

The question of whether our genes or our environment matter more for how long we live has lingered for decades. But a recent study published on April 21st, 2025 by Shenhar et al. may have finally tipped the scale. The authors reveal that genetics could account for twice as much of our lifespan as previously thought.

Environment plays a vital role throughout life, shaping early survival and long-term health. But its influence fades with age. Past a certain point, genetics becomes the dominant factor.

What is Heritability?

Heritability is the proportion of variation in a trait, like lifespan in this case, that can be explained by genetic differences between individuals. It’s not about how much your genes determine your life outcome, but how much they explain the variation across a population.

Researchers typically estimate heritability using:

• Twin studies: Comparing identical (monozygotic) and fraternal (dizygotic) twins.

• Pedigree studies: Tracking lifespans across extended families and generations.

• Genome-wide association studies (GWAS): Identifying specific genetic variants linked to longevity.

What the New Study Found: How Genetics Reclaimed the Spotlight

For decades, scientists estimated that only 7–25% of how long we live was inherited. But there was a major flaw in those numbers: they didn’t account for what kind of death occurred.

Shenhar et al. made a critical distinction between two types of mortality:

1. Intrinsic mortality – driven by biological aging and diseases like cancer or neurodegeneration.

2. Extrinsic mortality – caused by accidents, infections, wars, or external hazards.

This matters because extrinsic deaths introduce random variation unrelated to aging. This random noise masks the true genetic signals, making heritability look lower than it really is.

Using mathematical modeling and data from twin studies, the researchers showed that:

• Early deaths from extrinsic causes weaken the observed genetic link between twins.

• When these deaths are excluded, the genetic contribution becomes much clearer.

In more developed societies with lower extrinsic mortality, heritability estimates for lifespan increased dramatically, rising to over 50%.

Environment vs Genetics

Both environment and genetics matter but not equally and at a different time.

In early life, environment plays the dominant role: clean water, nutrition, healthcare, exposure to disease. These factors determine who makes it through infancy, childhood, and young adulthood. This accounts for public health and lifestyle.

But once you've reached midlife and old age, genetics takes over. The Shenhar study confirms what longevity researchers have long suspected: the longer you ...