The Genghis Khans of Europe

They say that about 1 in 200 people alive today is descended from Genghis Khan (or one of his brothers, if he had any.) Obviously most of the Great Khan’s descendants are in Asia; what about the rest of the world?

from A Handful of Bronze Age Men Could have fathered two-thirds of Europeans
from A Handful of Bronze Age Men Could have fathered two-thirds of Europeans

From the article:

“Tracking [Y chromosome] mutations allows scientists to create a family tree of fathers and sons going back through time. … Two-thirds of modern European men are found on just three branches (called I1, R1a and R1b). Our results show that these branches each trace their paternal ancestry to a surprisingly recent individual (shown as red dots in Figure 1). By counting the number of mutations that have accumulated within each branch over the generations, we estimate that these three men lived at different times between 3,500 and 7,300 years ago.”

Female genetics–mitochondrial DNA–show no such feature. “… when looking at this maternal tree, there is no similar explosion. This indicates that whatever factors were responsible for this pattern were specific to men.”

This seems reasonably strong evidence that we aren’t just looking at something that could be explained away as founder/bottleneck effect, because I would expect such an effect to act equally on males and females. However, I don’t know if anyone has adequately addressed the question of patrilocality.

On a potentially related note, another study came up with this graph of Y chromosome diversity over time

From,  A recent bottleneck of Y chromosome diversity coincides with a global change in culture
From,
A recent bottleneck of Y chromosome diversity coincides with a global change in culture

 

Now if you ask me, these look like they’re describing the same phenomenon, but the dates are supposedly different.

A couple of thoughts:

1. I really really wish they’d made the Y Chromosome graph bigger and spread it out more so I can actually see what’s going on. According to the article summarizing the paper, the Siberian population did not suffer a decrease in Y chromosome diversity at this time, but I can’t tell it from looking at the graph.

2. Wow, look at the African Y chromosome diversity drop and then never fully recover. The Near East Y-diversity (the orange part) shoots up much higher than it was initially after the drop, as does the European. If the suspicion that farming was the cause of the drop is correct, then it looks like African Y chromosomes never quite recovered–consistent with the theory that African horticulture has traditionally been easy enough for women to do, leading to polygyny, leading to a few males dominating most of the women and the other males being excluded, etc. See, eg, West African Marriage and Child-Rearing Norms vs. African American Norms. (I’ve got another post on the subject, but it’s not going up for a few more weeks.)

3. What’s been happening to mtDNA diversity in the past few thousand years?

 

So was it agriculture? Or were did agriculture just make people sitting ducks for horse-born invaders? Or perhaps both?