Evolving Thoughts

Evolution, culture, philosophy and chocolate! John Wilkins' continuing struggle to come to terms with impermanence... "Humanus sum, nihil humanum a me alienum puto" - Terence

Friday, May 19, 2006

Sorry for the silence, and chimp hybrids

I apologise for the lack of posts. My hindbrain (Powerbook G4 12") was out being serviced, and I (i) was stuck on a PC (*shudder* How do people work on those things?), and (ii) I got busy with other stuff, which may find its way here anyway.

So while I was incommunicado (is anyone ever communicado?) the "news" that humans and chimps were hybridising for several millions of years appeared in the New York Times, presaging an article in Nature. John Hawks has a nice takedown of this paper, although it has been hysterically dealt with by the media.

But what's the big deal? Hybrids occur between greatly differentiated lineages all the time. They aren't, though, common, and while many are sterile like the mule, many are also fertile and can back-breed into one of the parent species. Hawks mentions the lion-tiger crosses in genus Panthera, the tigon and the liger, which are fertile and not, respectively. Tigers (nine species or subspecies) and lions separated about 2 million years ago. Similarly, horse evolution has allowed a considerable amount of cross breeding between species that separated about 4 to 2 million years ago. When such things occur, the resulting process of genes crossing species boundaries is called introgression, and it is more common than we might think.

So why would the discovery, if it is, that genes occasionally cross from chimp to hominid lineages be any more unusual than the horse or Panthera hybrids? Obviously because we are involved. Our evolution is, after all, just ordinary evolution, no matter how unusual our brain size or other phenotypic traits. All species are unique (which is why we call them "species"). And the rate of introgression looks to be pretty rare anyway. It's not like Greatn Grandfather was out for a bit of chimp tail every Saturday night.

Now, some housekeeping. In the near future I will be travelling a fair bit, so I'll be reviving some old posts from the dusty archives. Moreover, this blog is moving. Stay tuned for an announcement. I'll leave this site up indefinitely, but you'll need to revise your RSS feeds and bookmarks when it does.