Arrrrrrrrrrrrg now I have to track down the full article meself
[news.stanford.edu]war-clan-structure-explain-odd-biological-event/
The full link is in there, and it is a good read. I had to post it as it is quite interesting, yet also a simple, common-sense hypothesis.
@Kohelath could not see the full link, only an image of the top of the page, that is why I relinked it. Maybe browser varience
@Davesnothere the interface isn't as intuitive as it could be, but the link is in the "Well duh, that figures" text at the top.
@Kohelath well duh, that went over my head