Writing in The Conversation about our own research! 
(also, you can read about my role in this work and some of the methods involved at: https://danielzadik.wordpress.com/my-research/ )
- Comment
- Reblog
-
Subscribe
Subscribed
Already have a WordPress.com account? Log in now.
Daniel Zadik Writing 
Interesting research. Is it possible the Y chromosome in these men helped them survive bubonic plague or some other disease? Or perhaps it helped them survive cold or famine?
LikeLike
Good thinking! I don’t like to say no for certain, but I think its unlikely for a few reasons.
There are very few genes on the Y chromosome, and what is there mainly effects only fertility. When such genes go wrong, that usually means they’re selected out of the gene-pool pretty quick. For this reason, it’s usually assumed that patterns in the Y chromosome tree are not caused by natural selection.
In addition, advantageous mutations would have to have happened independently at least twice in the tree. I.E. in I1 and R1 (the ancestor of R1a and R1b), which admittedly isn’t impossible. However, there must have been other branching points in the R1 tree before the R1a/R1b split, and these (or some of them (along with any other post-advantageous-mutation I’s) should have the same advantages we see in R1a, R1b and I1. The fact that we don’t see survivors from them (who would be visable as a deeper branching structure in or around our three branches long before the bottleneck happened in other branches) would mean that three advantageous mutations would have to have happened in quick succession just before the bottleneck, tho never earlier. That seems a little too convenient.
Also, (speaking off the top of my head) if some Y chromosomes gave you a resistance or susceptibility to a particular disease, might we not expect to see that one sex was more susceptible than the other? I don’t know whether that’s something we know about historical plagues, but maybe that might be the kind of thing that would have been recorded. As for cold or famine, might we not expect the advantageous traits to have spread even further if they were so generally useful?
We are not saying for sure that the pattern we see is caused by a Yamnaya expansion, but its where I’d put my money! Hopefully future work will provide more evidence and maybe give us a more definitive idea of the cause.
LikeLike
PS, it would be interesting to test European DNA pre-1300 CE (before the first wave of bubonic plague) and see if it differs post-1700 CE (after the second wave of bubonic plague) — or maybe that has already been done?
LikeLike
That would be nice! We were looking at modern DNA and inferring a history, so we didn’t look for a change at any particular time. We looked for patterns and then estimated their age. And the ages we got for a probable bottleneck were the ones given in the article. The field is moving fast, including studies that sequence archaeological/palaeontological samples, so who knows what cool stuff will be turned up!
LikeLike
Correction: it would be interesting to test European DNA pre-500 CE (before The Plague of Justinian, the first wave of bubonic plague in Europe) and see if it differs post-1700 CE (after the last wave of bubonic plague in Europe) — or maybe that has already been done?
LikeLike