Humans appear to be evolving to hit puberty later and those who start at an older age live longer, a genetic study has found.

Using data from over 200,000 people, scientists also discovered that the genetic variants linked to heart disease, obesity and high cholesterol appear less frequently in people who live longer.

The research, published in PLOS Biology, provides an insight into evolution in action, showing how natural selection is slowly weeding out unfavourable traits and adapting to our changing lifestyles.

Genetic traits evolve when mutations offering survival arise and, generally speaking, people who have these traits are predisposed to live longer and pass on their mutations to more offspring. The mutation eventually becomes more common within the general population, increasing survival of the species.

Natural selection resulted in humans walking on two legs, having opposable thumbs and larger brains in changes that took place over thousands if not millions of years—but miniscule shifts are happening all the time.

The team led by Columbia University’s Hakhamanesh Mostafavi looked at the genomes of 210,000 people from Europe taken from the Resource for Genetic Epidemiology Research on Aging (GERA) Cohort and U.K. Biobank. To make up for the lack of older people in the dataset, the team used the age of parental death for people in the Biobank genomes as a proxy.

Researchers tested whether the frequency of an allele—a variant form of a given gene— varies across different ages and accounts for variation within ancestry. They looked at 42 common traits, such as body mass index (BMI) and height, and worked out whether this was involved in survival. From this, they found just two common variants that had a big effect on age-specific mortality.

“We find that variants that delay puberty timing are enriched in longer-lived parents, consistent with epidemiological studies. Similarly, in mothers, variants associated with later age at first birth are associated with a longer lifespan,” the team wrote, adding that a one year delay to puberty was associated with a reduced death rate by between three and four percent.

They also found signals for variants relating to cholesterol levels, risk of coronary artery disease, BMI and asthma appear less often in longer-lived people. One of the genetic variants that affected mortality is also linked to Alzheimer's disease—the team found in women over 70, there was a drop in the frequency of this specific gene, indicating that women with one or two copies of it tend to die earlier.

"It's a subtle signal, but we find genetic evidence that natural selection is happening in modern human populations," study co-author Joseph Pickrell said in a statement.

The researchers note that environment also plays a major role in lifespan, with Mostafavi saying that traits linked to longer lifespans now may not necessarily be useful in the near future, as conditions change. They also say the changes documented could arise from other components relating to fitness. To better understand what influence these mutations have and why they arise, researchers will need to study the “millions of samples in the pipeline,” they said.