Toronto: Humans, like all other organisms on Earth, are still evolving in response to the environment, a new Canadian study has suggested.

By studying an island population in Quebec, a team from the University of Quebec in Montreal discovered a genetic push toward younger age at first reproduction and larger families, a finding they claimed is the first direct evidence of natural selection in action in a relatively modern human population.

"Whether humans could or could not evolve in modern time could have interesting implications," study author Emmanuel Milot was quoted as saying by LiveScience.

It could help us understand changing trends for the different traits of a population, he said.

Past studies have hinted our species continues to evolve, with research showing changes to hundreds of genes in the human genome over the past 10,000 years; in addition, skull measurements suggest our brains have been shrinking over the last 5,000 years or so.

The latest study, published in the journal Proceedings of the National Academy of Sciences, used data from 30 families who settled on île aux Coudres, located in the St Lawrence River outside of Quebec City, between 1720 and 1773.

A church on the island held historical records of all births, deaths and marriages on the island, from which the researchers were able to build intensive family trees.

They analysed data from women who married between 1799 and 1940, comparing their relations, any socio-economic or cultural differences, and the age they had their first child.

It was found that over a 140-year period, age at first reproduction dropped from 26 to 22, with somewhere between 30 per cent and 50 per cent of this variation being explained by genetic variation in the population, not by other factors, such as changes in cultures or social attitudes.

Milot said: "We think, traditionally, that the changes in human population are mainly cultural which is why a non-genetic hypothesis is given priority over a genetic or evolutionary hypothesis, whether or not there is data to support that.

"We have data that we analysed from the genetic and non-genetic point of view, and we find that the genetic factors are stronger."

Because of the populations' lack of birth control, the families ended up being very large, and since fertility wasn't altered by outside influences, each couple was likely to reach maximum fertility.

The researchers didn't look at which genes might have changed over time, but they suggested that reasons for the age change could include differences in fertility and how early a woman hits puberty, or even heritable personality traits that would nudge a woman to procreate earlier. These factors would be changing in response to the natural selection for a higher number of kids overall.

Milot said: "In that particular population, selective pressure seemed pretty constant for the study period. May be it has to do because it has a newly founded population and it was not disadvantageous to have big families.

"What we learn from that population is that evolution is possible in relatively modern times in modern humans. Where it is going to occur and in what ways is a different question."

(Agencies)