Research: Longevity Brings Unavoidable Risks for All Humans

Humans are now living longer than previous generations, yet this additional lifespan is often accompanied by a decline in health quality. A recent study reveals the reasons why longevity comes at a ‘high price’ and why diseases in old age seem to be a difficult risk to avoid.

The research, published in the journal Nature Reviews Genetics, examines the concept known as the ‘selection shadow’. This theory, proposed since the mid-20th century, can now be proven thanks to large-scale modern genetic data.

Simply put, this theory explains that the strength of natural selection decreases with age. Evolution is most effective at maintaining bodily functions during the fertile and reproductive years. Once an individual passes the age of having offspring, evolutionary pressure becomes very weak—as if covered by a ‘shadow’—meaning harmful mutations or detrimental genes in old age are no longer naturally eliminated.

There are two main mechanisms explaining this risk. First is the accumulation of harmful mutations, where genetic changes that only manifest symptoms in later life are not detected by natural selection, thus continuing to be inherited and accumulating across generations.

Second is genetic trade-offs, where certain genes that are highly beneficial in youth—for example, supporting fertility and growth—actually increase the risk of diseases such as cancer or chronic inflammation in old age. Evolution retains these genes because the benefits during youth far outweigh the disadvantages that only become apparent in later life.

Researchers Handan Melike Dönertaş and Linda Partridge analysed genetic data from hundreds of thousands of people and found strong evidence that this concept is indeed occurring in humans.

“Genomic advances allow us to prove that genes involved in chronic inflammation, stem cell exhaustion, and declining organ function are indeed not well-selected after reproductive age,” explained Dönertaş from the Fritz Lipmann Institute, Germany.

A concrete example is gene variants that aid fertility in the 20s and 30s, which have been proven to increase the risk of heart disease or cancer in those aged 60 and above. Within an evolutionary framework, these cancer-causing genes are worth maintaining because they function to ensure the ‘continuity’ of the species.

These findings are changing the perspective of researchers. The goal of research should no longer merely be to extend lifespan, but to extend the period during which a person remains healthy and fit—known as extending ‘healthspan’.

“The selection shadow that allows the ageing process to occur now provides a framework to reduce its adverse impacts. We can develop interventions that suppress the harmful effects of genes that are beneficial in youth but dangerous in old age,” said Partridge from University College London.

Further studies on extremely long-lived animals, such as naked mole-rats, are also being conducted to learn how they overcome this ‘selection shadow’ so that the findings can be applied to humans.

Amidst the global trend of increasing life expectancy, these findings serve as an important reminder. While longevity is a desire, the risk of disease in old age is embedded within the evolutionary design of the human body. By understanding these mechanisms, the medical world is expected to not only treat the symptoms of old age but also target the genetic root causes, so that later life can be lived more healthily and independently.