Genetics play a much larger role in lifespan than previously thought

For decades, scientists have debated whether long life is mostly a matter of healthy habits or inherited biology. A new analysis suggests the balance may tilt more strongly toward genes than previously thought.

By reexamining decades of twin records, researchers now estimate that genetics could account for about 55 percent of the differences in how long people live – far higher than many earlier estimates.

That shift doesn’t sideline lifestyle, but it does sharpen the question of whether there is a built-in biological ceiling to human life.

To find that signal, scientists had to separate deaths driven by random outside hazards from the slower internal processes of aging itself – a distinction that dramatically clarified the genetic picture.

Reanalyzing lifespan through twins

Twin registries in Denmark and Sweden, which have followed paired lives from birth to death, provided a critical lens for isolating that inherited influence.

Reanalyzing those records, Dr. Ben Shenhar at the Weizmann Institute of Science showed that separating sudden outside deaths from age-driven decline revealed a far stronger genetic signal.

Once researchers separated deaths from accidents and infections, identical twins tracked each other’s longevity far more closely than earlier calculations indicated.

Yet even with that clearer alignment, the remaining variation left room for forces beyond DNA, setting up a deeper look at how outside hazards have long blurred the picture.

Early deaths distort data

Early deaths from a crash or infection can end a life before genetics has time to shape the slow diseases of old age.

The researchers describe these outside causes of death as extrinsic mortality – losses driven by accidents, infections, predators, or other external forces rather than the body’s internal aging process.

For decades, many lifespan estimates mixed those sudden losses with age-related decline. That blending blurred the picture.

Earlier studies suggested genes explained anywhere from 6 to 33 percent of human life span, leaving wide uncertainty about how much DNA really shapes life itself.

But when researchers separated outside deaths from internal biological decline, the signal sharpened.

A closer look at shared genes

After removing extrinsic mortality, identical twins tracked each other’s longevity much more closely. With fewer random hazards in the way, shared genes became easier to see.

Using separate tracks for outside and inside deaths restored the family resemblance that twin studies rely on.

As a result, the genetic share of lifespan looked closer to other complex traits – and it reopened the search for the biological limits that may shape how long we live.

The impact of modern safety

Over the past century, daily life became less deadly. Cleaner drinking water, widespread vaccines, antibiotics, safer workplaces, and better emergency care dramatically reduced deaths from infections, accidents, and other sudden threats.

As those early hazards declined, something interesting happened in the twin data. People simply lived long enough for aging biology to matter more.

In twins born later in the 1900s, inherited differences showed up more clearly in who reached old age.

Even twins raised in different homes still resembled each other more than chance would predict once early-life dangers were stripped away.

In today’s relatively safer world, genes can account for more of the variation in lifespan – though everyday habits still shape risk in powerful ways.

The role of heritability

When researchers say genes explain about 55 percent of lifespan differences, they’re talking about heritability – a population-level statistic.

Heritability measures how much variation between people at a given time and place is linked to genetic differences.

Change the environment, and that number can change too. If fewer people die in accidents or from infections, biology becomes a bigger filter. If pollution rises or health care falters, environmental forces may loom larger again.

For individuals, though, genes are not destiny. A dangerous job, chronic stress, heavy drinking, or long-term exposure to air pollution can still shorten life, no matter what your DNA says. Heritability speaks in probabilities, not personal guarantees.

Longer life isn’t just DNA

Fatalism can creep in when people hear genes matter, especially in a culture selling supplements as the answer. For readers tempted to quit trying, one line from Shenhar kept diet and exercise in view.

“The message of our paper is not that lifestyle, exercise and diet are not important,” said Shenhar.

Lifestyle still shapes the remaining 45 percent because habits change inflammation and blood sugar, which feed many age-linked diseases.

Families with long-life genes

People who live past 100 rarely just “get lucky.” Many of them manage to avoid major diseases for decades, suggesting their bodies are wired to better withstand the wear and tear of aging.

That’s why scientists are so interested in their families. Protective genes may help cells repair damage more efficiently or slow the biological processes that lead to heart disease, dementia, and other age-related illnesses.

But the search hasn’t uncovered a single magic longevity gene. A recent review found that consistent genetic signals are surprisingly rare – and when they do appear, they tend to slightly tilt the odds rather than erase risk entirely.

That reality is pushing researchers toward much larger genetic studies. Scientists are sequencing thousands of long-lived families, recognizing that meaningful patterns emerge only when they analyze millions of small genetic differences together.

Many genes build long life

There’s no single “long life” switch in the human genome; instead, lifespan is polygenic, shaped by many genes with small effects across the body.

That makes prediction tricky. Two centenarians may both reach 100 in good health, yet carry very different combinations of protective variants.

It also explains why direct-to-consumer genetic tests often promise more than they can deliver. The reports usually capture only a slice of the picture.

They can miss rare gene interactions and overlook decades of lifestyle factors that interact with biology in complex ways.

In the end, long life looks less like a single genetic jackpot – and more like a slow accumulation of small advantages stacked over time.

Life between genes and chance

The edges of that split remain fuzzy. Infections and falls, for example, sit somewhere between pure bad luck and built-in biological weakness.

Some people inherit immune defenses that clear viruses faster, meaning a death labeled as “external” can still reflect underlying biology.

Twin research also assumes shared homes shape both siblings in similar ways, and much of the historical data comes from Northern Europe in past centuries.

Researchers need clearer death records and studies spanning more diverse populations to determine how stable this estimate truly is – and whether they need to redraw its boundaries.

Separating random hazards from biological wear has sharpened the genetic story, while leaving lifestyle and chance as meaningful partners.

Next, larger genetic databases paired with more precise cause-of-death data should reveal whether this proposed genetic limit holds across today’s global populations.

The study is published in the journal Science.

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