In a study published in the journal Genome Research, researchers have found that genetic diversity in male lineages dramatically declined between 4,000 and 8,000 years ago. Genetic diversity in females, however, rose during the same period.
Lead author Melissa Wilson Sayres, an assistant professor at the School of Life Sciences at the Arizona State University, explained that instead of "survival of the fittest" becoming the guiding thought at the time, people became more preoccupied with accumulating wealth and power. This led to reproductive success for men who were more "socially fit," who were also fewer in number than biologically endowed males.
Decrease in genetic diversity, or a bottleneck, has been previously recorded. It happened about 50,000 years ago when a certain African subset left their homeland, migrating across the globe. Signatures of the bottleneck appear in non-African populations as either acquired from both parents or just along the genetic line of the father or the mother.
Senior author Toomas Kivisild from the Division of Biological Anthropology at the University of Cambridge said that the bottleneck from 4,000 to 8,000 years ago occurred when people in various parts of the world became sedentary farmers.
Researchers gathered DNA samples from the blood or saliva of 456 males in seven regions across five continents, including Oceania, Europe, South Asia, Africa and the Andes. They studied the Y chromosome and the mitochondria. The Y chromosome is only passed down in males while genetic material for the mitochondria only comes from females. Applying statistical and computer modeling led to the identification of the major bottlenecks in the genetic history of humans.
With certain populations more susceptible to particular conditions, the results of the study are believed to have implications to human health. For one, the more varied the genes are in a population, the greater the chances that population has of surviving and thriving. Unfavorable genetic traits will also be less likely passed down.
"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," said Wilson Sayres.
The next step for the researchers is to gather more DNA samples, increasing diversity and not just quantity, and working with sociologists and anthropologists to understand findings under a different light.
Several institutions provided funding support for the study but the University of Tartu and Estonian Biocentre provided primary aid. Researchers from across 66 institutions across the globe participated in the research.
Photo: Matthias Ripp | Flickr