Tian chen zeng, marcus feldman and alan aw. Image: marcus feldman
Stanford researchers demonstrate that a combination of patri-clans and wars lead to the "neolithic Y chromosome bottle neck" five to seven thousand years ago
A team of scientists researching at the elite northern california university of stanford has published a study in the current ie of the journal nature that solves a problem that has preoccupied not only prehistorians and human geneticists since its discovery in 2015: it is about the "neolithic Y chromosome bottle neck", who appeared in the male lineage of mankind five to seven thousand years ago.
At that time, the genetic diversity of Y chromosomes in europe, asia and africa decreased drastically. So drastic that the ratio of female to male progenitors was eventually 17 to 1.
Bottlenecks in lineages are nothing unusual in biology. Often they are accompanied by weather or other natural disasters. But without human intervention, they usually affect both male and female ancestors. This is an indication that the neolithic Y chromosome bottle neck could have cultural causes or contributory causes.
Another indication is the fact that the bottleneck appeared immediately after a time when livestock farming was spreading. Empirically, this pastoralism – and especially herding – is often accompanied by patrilineal social organizations aligned with paternal lineage. If the lineage is concretely traceable, it is called a patri lineage; if it is too complex to memorize, but believed to be from a patri clan, it is called a patri lineage.
One of the consequences of this form of organization is that all men in a patri-clan are biologically related to each other, which is not the case for women in patrilineally organized exogamous societies. They change clans when they marry.
Potential model for collaboration between different academic disciplines
Sociologist tian chen zeng, mathematician alan aw, and biologist marcus feldman wondered whether the bottleneck might be explained by wars that wiped out many patri-clans (and with them their Y chromosomes). To this it was fit that the bottleneck was more pronounced in europe, west asia and india than in southeast asia, where shepherding did not play so rough a role.
To test their hypothesis, zeng, aw, and feldman developed a computer simulation in which men organized into patri-clans could fight over resources and die in the process. This model showed that Y chromosome diversity actually decreased as drastically as in reality five to seven thousand years ago. In models with non-patrilineally organized clans, this effect did not emerge.
Feldman now wants to test the model on the betsileo in the highlands of madagascar, whose recent history lends itself to it. The co-director of the stanford center for computational, evolutionary and human genomics also sees his research, requested by the morrison institute for population and resource studies and the U.S. National science foundation, as a potential model for fruitful collaboration between different academic disciplines that can shed light on how culture and evolution interact.
Horses and foxes
Another example of this interaction was published in april in science advances by researchers from the leibniz institute for zoo and wildlife research (IZW) in berlin and the university of potsdam. Analyzing genetic material from horse teeth and bones from asia and europe, they found that most of the world’s approximately 60 million horses today are descended from a single stallion that was born about 3.000 years ago had such desirable characteristics that its descendants were clearly preferred when mating accordingly.
A very important desired trait in domestic animals – the ability to be tamed – could be genetically associated with a tendency to spotted fur, as shown by a breeding experiment started in russia in the 1950s: together with this biologically inherited readiness for taming, the animals also developed a spotted fur and especially a colored forehead spot, as it is known especially in horses. Also the tame foxes are descended from a single male named ember.