How much do your genes determine your lifespan? This is a question that fascinates us, and one that has been debated for decades. For years, the answer seemed set in stone. Genes account for about 20-25% of the variation in human lifespan, with the rest due to lifestyle and environment.

However, a new study has been published science refute this view and suggest that the genetic contribution may be quite high.

The researchers say this is because previous estimates did not account for how causes of death changed over time. A century ago, many people died from what scientists call external causes: accidents, infectious diseases, and other external threats.

Today, at least in developed countries, most deaths are caused by endogenous causes. It is the gradual decline of the body due to aging and age-related diseases such as dementia and heart disease.

To get a clearer picture, the research team analyzed a large group of Scandinavian twins, carefully excluding deaths from external causes. They also studied twins and centenarian siblings who grew up apart in the United States.

Subtracting deaths from accidents and infectious diseases, the estimate of the genetic contribution jumped dramatically from the well-known 20-25% to about 50-55%.

This pattern can be understood by looking at individual diseases. Genetics explains much of the variation in dementia risk, has an intermediate effect on heart disease, and plays a relatively modest role with respect to cancer. The genetic component appears to naturally grow larger as the environment becomes more favorable, the population ages, and diseases caused by the aging process itself become more common.

our genes are not yet strong

But this is where interpretation becomes important. A higher estimate does not mean that the genes are suddenly more powerful, nor does it mean that they only influence half the chances of reaching old age. What has changed is the environment, not the DNA.

Consider human height as an example. A hundred years ago, how tall you grew depended largely on whether you had enough food and whether childhood illnesses stunted your growth.

Today, almost everyone in wealthy countries receives adequate nutrition. Because these environmental differences have narrowed, genetic differences now account for most of the remaining variation in height. Not because nutrition is no longer important, but because most people are now able to reach their genetic potential. However, regardless of genetics, malnourished children do not grow taller.

The same principle applies to longevity. As we improve vaccinations, reduce pollution, improve diets, and adopt healthier lifestyles, we have reduced the overall impact of environmental factors.

As environmental variation decreases, the proportion of remaining variation attributable to genetics (what scientists call “heritability”) increases by mathematical necessity. The previous estimate was correct. They simply reflect different historical circumstances.

This reveals something fundamental. Heritability is not a fixed biological property, but a measure that depends entirely on the population and situation being observed. The traditional 20-25% figure represents the actual lifespan experienced by historical populations where external threats loomed large.

The new 50-55% estimate represents an alternative scenario in which these threats are largely eliminated and exhibits essentially different characteristics.

Major figures regarding life expectancy that exist in the world “50% is inherited” There is a danger of being misunderstood to mean that genes determine half of a person’s life chances. In reality, a particular individual’s genetic contribution can range from very small to very large, depending on his or her circumstances.

There are countless paths to longevity. Some people have a strong genetic profile that protects them in difficult situations, while others compensate for less favorable genetic traits with good nutrition, exercise, and health care. Each person represents a unique combination, and different combinations can lead to exceptional longevity.

Which combination is the most common depends entirely on the population, people’s living conditions and age. It will be interesting to see how these patterns evolve, although they will not go away completely, as external causes of death continue to decline in the real world.

The authors of this latest study acknowledge that about half of the variation in lifespan still depends on environment, lifestyle, health care, and random biological processes such as uncontrolled cell division in cancer. Their study calls for renewed efforts to identify the genetic mechanisms involved in aging and longevity. Understanding how different genetic factors interact with different environments is perhaps the key to explaining why some people live much longer than others.

This study provides valuable insight into how different types of mortality have shaped our understanding of lifespan. However, the results are best understood as showing how heritability changes in different situations, rather than establishing a single universal genetic contribution to our longevity.

At the end of the day, both genes and environment are important. And perhaps more importantly, they matter together. So whether you think it’s good news or bad news, we’ll probably never have a simple answer to how much of our lifespan is determined by genes alone.