Genetic epidemiology: Importance of population genomics

A team of researchers traces the contributions of females and males to reproduction

Did women and men contribute equally to the lineage of contemporary populations? Did our ancestors, Homo sapiens, lean more toward polygamy or monogamy? To answer these questions, Dr. Damian Labuda, an investigator at the Sainte-Justine University Hospital Research Center and a professor at the Department of Pediatrics of the Universit- de Montr-al, headed a team that analyzed genomic data from three population samples of African, Asian and European origin. The study's findings are published in the most recent issue of the American Journal of Human Genetics.

In a strictly monogamous population, one would expect to have an equal number of breeding females and males and, therefore, a breeding sex ratio of one female to one male. In a population where males tend to have more than one female mate, more females than males contribute to reproduction; for this reason the breeding ratio exceeds one. The authors of this study estimate that the breeding ratio varies between 1.1 and 1.4 according to population: 1.1 in Asia, 1.3 in Europe and 1.4 in Africa.

Modern man or Homo sapiens would, therefore, usually have been monogamous while exhibiting tendencies toward polygamy over the course of evolutionary history. These findings are consistent with studies in evolutionary psychology and anthropology that depict contemporary human populations.

To estimate the breeding sex ratio based on genomic data, the authors developed a novel method to capitalize on how females carry two X chromosomes, whereas males carry only one. Consequently, during the recombination process, X chromosomes can only exchange their genetic information with females.

An excess of breeding women causes an excess of recombination signals in terms of quantifiable X chromosomes. This new method is more reliable than the previous approaches that quantified the breeding ratio using another method. It may be applied to any species for which data on genomic diversity are available.

"Our results allow better understanding of the genetic population structure and demonstrate once more the importance of population genomics in genetic epidemiology. Being able to analyze the female-male ratio in the history of humans provides new insights into the evolution of our species, which, in turn, leads to better understanding of ourselves through the knowledge of our past," says Dr. Labuda.