Evolution occurs in response to outside forces that weed out whatever individuals are least fit to survive those pressures, allowing those better-fit individuals to survive and reproduce. However, since humans radically alter their environments, some researchers have questioned whether natural forces of selection continue to act upon our species. For instance, agriculture can generate surplus food that can insulate us from many ills of the world.

The findings, detailed online today (April 30) in the journal Proceedings of the National Academy of Sciences, add to accumulating evidence of our continued evolution. For instance, past research has suggested the human brain has been shrinking over the past 5,000 years. Another study of an island population in Quebec found a genetic push toward a younger age at first reproduction and larger families.

To explore this debate further, scientists examined church records of nearly 6,000 Finns born between 1760 and 1849, which detailed information on births, deaths, marriages and economic status. The data enabled the researchers to investigate human patterns of survival and reproduction and compare them with other species — genealogy is very popular in Finland, and the country has some of the best available data for such research.