[WARNING – BSG SPOILER] PopGen’s teachable moment – Hera, mtEve and the fate of the BSG survivors

I just finished watching the last episode of Battlestar Galactica. You could see for a while that it was going to turn out that we were all descendants of the survivors, but I’m embarrassed to say that I didn’t see the Hera – mitochondrial eve connection until the raptor swooped over the plains of east Africa.

After the episode ended, I started poking around to see what people are saying about the ending, and I was surprised at how often I came upon some version of the following exchange (from rc3.org):

There really is a Mitochondrial Eve — she is the earliest common ancestor all humans alive right now share. (I believe she lived about 90,000 years ago, so the 150,000 number on the show is wrong.)

What this implies is that none of the humans or cylons who wind up on Earth (other than Hera) are able to successfully reproduce, or that all of their progeny die out. Hera’s offspring are the only ones who make it. And indeed, none of the indigenous residents of Earth will have produced successful offspring, except through Hera.

Reader Rob then responded:

No, she’s the last common matrilineal ancestor of all living humans- all humans alive today have her mitochondrial DNA. She is NOT, however, the last common ancestor of all humans alive today… It should be remembered though that this does not mean that other women didn’t leave descendants whose are still alive. Mitochondrial-DNA is only inherited on the female side; a woman who had 10 male children but no females would be a mitochondrial dead end, but could have theoretically millions of descendants alive today.

This is hardly the only such exchange. Everywhere people are talking about BSG’s finale, they’re talking about population genetics. And they’re mostly getting it wrong. The “no other survivors have descendants” is the most common misconception, but others include: Hera being half-human, half-cylon means we all are; Hera had to have had at least one daughter (actually she would have had to have had at least two); the indigenous population must have died off; etc…

But on all the blogs and forums I’ve visited, people have corrected these misconceptions. It’s like there’s this big, organic lesson in human population genetics going on out there, as people collectively wrestle with the concept of mtEve, and – amazingly – generally converge on something approximating the right answer. I think it’s kind of cool.