The Cute New Boyfriends Theory

Treasured beliefs die hard. When looking at European prehistory and population replacement, it was a shock to some anthropologists to think that it was all so, so violent. With some it was tied to the idea that primitive peoples were not all that violent, but only in the later years with the supposedly "civilised" men in the Mediterranean and especially Europe did the rest of the world learn violence. Hierarchy and stratification was the problem. Before that, most tribes were more egalitarian, as the few remaining hunter-gatherer tribes who have been driven to marginal lands and existences are now. 

If you think that you sniff an argument against capitalism and in favor of communism buried under that I will nod in agreement.  If you wait long enough, that argument leaks out.

One of the places it isshowing up now is in the Indo-European/Yamnaya/Corded Ware replacement of the European farmers who were in place beforehand (ushering in a thousand-year Dark Ages, BTW). Entire y-haplogroup lineages disappear in less than a century, replaced by R1b. From that bottleneck people started moving around and admixing again, so R1b is merely the dominant, not the exclusive lineage now.  But at the time they ran the table.  Lots of mtDNA lineages, the female-to-female lines remained diverse, indicating that they didn't kill all the women, they took them as victims first, concubines next, and wives thereafter. 

This is stretched to maintain that not all the replacement was violent, that some of it was these masculine, horse-riding steppe invaders outcompeted the local men, sweeping the local girls of their feet, so that they dropped their old boyfriends in favor of new ones they liked better. I have actually heard female anthropologists use similar language, fairly giggling in a worldly-wise way. 

Where to begin? If these men had simply been outcompeted, 30% in the first generation, 30% in the second generation, etc, a few of their lineages would have snuck through. Even if the conquered were now slaves. Even apes have strategies for distracting the chiefs so that your pals can sneak around the back door, hoping it will be your turn next time. If they were allowed to be alive at all, some of the previous farmers would have sided with the victors, or their sons would, and in the following generations who came from what lineage would be less clear...to them.  But not to us, who now have the DNA. The pattern I just described does happen.  You can see in in the British Isles in the Saxon invasion, the Viking invasion, and the Norman invasion.  In recorded history, it the far more common pattern in Europe. (Other places, not so much.) But you can see the weakness of this arguement when you envision what complete replacement really means.

It does not mean that every single encounter was violent. Some clans would see the writing on the wall and give their daughters semi-willingly, as that is what they had been doing beforehand anyway, back when the opponents and allies were more closely related (or at least not all R1b.) Some Iberian mixtures seem to be at least somewhat cooperative, and after the first generation, a lot of them would be. But these were not the norm.

Second, where on earth does the idea come from that these women had any choice in the matter? Except in warfare and other violent expansion, even the young men weren't given much choice. As soon as things settled down even a little, chieftains, and then families, decided who the tribe's boys were going to mate with and pretty much assigned them out. To think that in such a situation the girls were whispering "Aren't these new fellas simply scrumptious?  I'm going to try and catch the eye of that one over there, the one with the feather in that dashing cap." Women having much say is rather um, recent. Sexual selection did operate, but most of that would be secretive.

Third, and this is more speculative, the succeeding waves of steppe invaders are described as quite unattractive - short (because hunched), scarred, unshaven in the extreme, smelling funny, mostly violent. How is that the answer to a maiden's prayer?