Decline in the number of males involved in reproduction during the period of global growth

In a study published recently in Genome Research, scientists from University of Cambridge, Estonian Biocentre, University of Tartu, Arizona State University and 64 other institutions around the world discovered that accumulation of material culture during the middle and late stages of Neolithic, four to eight thousand years ago, is associated with a dramatic decline in genetic diversity in male lineages whereas female genetic diversity was on the rise.

It has been widely recognized that a major bottleneck, or decrease in genetic diversity, occurred approximately 50 thousand years ago when a subset of humans left Africa to colonize the rest of the world. Signatures of this bottleneck can be seen in most genes of non-African populations regardless of whether they are inherited from both parents or, as confirmed in this work, only along the father’s or mother’s genetic lines.

“Most surprisingly to us, we detected another, male-specific, bottleneck during the period of global growth. The signal for this bottleneck dates to a time period when humans in different parts of the world had already for thousands of years been sedentary farmers,” said senior author Toomas Kivisild from the University of Cambridge’s Division of Biological Anthropology.

View an infographic of the research story here.

Melissa Wilson-Sayers, one of the lead authors from the School of Life Sciences at Arizona State University, added: “Instead of ‘survival of the fittest’ in biological sense, the accumulation of wealth and power may have increased the reproductive success of a limited number of socially ‘fit’ males and their sons.”

The researchers said studying genetic history is important for understanding underlying levels of genetic variation. Having a high level of genetic diversity is beneficial to humans for several reasons. First, when the genes of individuals in a population vary greatly, the group has a greater chance of thriving and surviving — particularly against disease. It may also reduce the likelihood of passing along unfavorable genetic traits, which can weaken a species over time.

According to Monika Karmin, co-author from University of Tartu, their findings further stress the differences in human male and female genetic histories which also may have implications related to human health.

“The striking difference in the number of reproductive males and females in that time window certainly affected the diversity of genes on the male genetic line,” said Karmin. “We know that some populations are predisposed to certain types of genetic disorders. Researchers worldwide are trying to figure out what the underlying genetic structure is, so now also the fact that the male part of human lineages has gone trough a severe bottleneck has to be considered.”

“When a doctor tries to provide a diagnosis when you are sick, you’ll be asked about your environment, what’s going on, and your genetic history based on your family’s health. If we want to understand human health on a global scale, we need to know our global genetic history; that is what we are studying here,” added Wilson-Sayers.

The researchers believe this will be relevant for informing patterns of genetic diversity across whole human populations, including informing about susceptibility to diseases, independently in different populations.

Adapted from an Arizona State University press release.