The research team analyzed genetic data from more than 70,000 Taiwan Biobank participants, identifying multiple genetic variants showing signs of ongoing natural selection.

A Striking Pattern in Red Blood Cells

Of those variants, 159 were less common in younger age groups — a pattern consistent with purifying selection, the process through which harmful genetic variants become less common over generations.

The findings were particularly consistent for red blood cell traits. The researchers identified 149 variants that were less common among younger participants and were associated with larger red blood cell volume and lower hemoglobin concentrations. The only red blood cell–associated variant that was more common in younger participants showed the opposite pattern: smaller red blood cell volume and higher hemoglobin concentrations.

 

Together, these findings suggest that natural selection may be reducing the frequency of variants associated with larger red blood cells.

A Possible Legacy of Malaria

One possible explanation lies in Taiwan’s history of infectious disease. Malaria was once endemic in Taiwan, which received certification for malaria elimination in 1965. Throughout human evolution, malaria and other infectious diseases may have exerted strong selective pressure on red blood cell traits. Taiwan Centers for Disease Control

The researchers suggest that the patterns they observed may partly reflect the legacy of those past disease pressures. As infectious disease exposure and living conditions change, genetic variants may face different selective pressures.

The possible connection to malaria remains a hypothesis, rather than a demonstrated cause of the patterns identified in the study.

Clues to Cancer Risk and Precision Medicine

The team also found signs of natural selection in BRCA1, BRCA2 and MLH1, genes involved in DNA repair and cancer susceptibility. In BRCA1, the researchers identified a rare haplotype — a group of genetic variants inherited together — carrying multiple disease-causing variants. This haplotype was less common in younger age groups.

Such rare, population-specific variants provide important genetic information for assessing disease risk and advancing precision medicine. For Ko, the findings highlight how comparisons across age groups can offer a window into evolution as it unfolds.

Natural selection is not confined to humanity’s distant past, he said. Its effects remain evident in contemporary populations, offering a new perspective on the relationship among human evolution, health, and disease.

First author Jing-Lian Chen (second from left) with Professor Wen-Ya Ko (far right), members of his research team, and Professor Yoko Satta (second from right)