Y chromosome: Ancient male population explosions discovered through modern DNA

Ancient male population 'explosions' have been discovered using the DNA from modern men. A comparison of the genetic variation in the Y chromosome (found only in men) has provided a new picture of the historic evolution of male population numbers and dispersion around the globe.

Findings revealed, unexpectedly, that all 1,200 men came descended from a single man who lived approximately 190,000 years ago. Following this, however, there were a series of population spikes between 55,000 and 4,000 years ago.

The Y chromosomes of men is passed from father and son so can tell scientists a great deal about our ancestors. By using DNA of modern men, scientists can build a tree to show how men are related to one another.

The research, published in the journal Nature Genetics, is the largest ever study into the differences in the Y chromosomes of men around the world. The study is based on free data extracted from the 1000 Genomes Project, the biggest public catalogue of human variation and modern genotype data.

Population movement and expansions

The researchers, from the Wellcome Trust Sanger Institute, analysed variation of the Y chromosome of more than 1200 men, from 26 population groups around the world. Lead authors Dr Chris Tyler-Smith and Dr Yali Xue say the the phylogenetic tree derived from this data displays striking structural features.

"We can see some parts of the tree look more like bushes, where we identify new mutations, new Y chromosomes emerging. These parts correspond to massive expansions in the number of males, in short amount of time, in some parts of the world" Tyler-Smith told IBTimes UK.

The scientists say at least two of these expansions can be linked to historic population movements. In the first case, they identified a significant male population expansion in Asia around 50-55,000 years ago, a time during which men were leaving Africa for other continents.

The second event they charted was the arrival of men in the Americas, roughly 15,000 years ago. The phylogenetic tree reveals the emergence of a great number of Y chromosome mutations at that time, in this part of the world. This reflects the fact men settled in the Americas, and subsequently populated the region as they started having a great number of male offspring.

Technological improvement

Other events surrounding male population explosion were less expected by the study's authors. For example, they observed additional expansions between 3,000 and 7,500 years ago, at different times during this period. "Here, we see a specific male population expansion, which only corresponds to a small subset of Y chromosomes" Yali Xue said.

Genetic analysis does not allow scientists to know for sure what happened, but the authors speculate that improvement in technology led to profound changes in social structures, determining which male individuals were more likely to pass on their genetic characteristics.

"What we think likely happened is that advances in technology led to more hierarchical societies led by small groups of men whose privileges allowed them to have a lot of sons, with their descendants following their example after them", says Tyler-Smith.