Has anyone read Hawk’s latest blog about Neandertal mtDNA? He answers some emailer’s questions and goes on a long explanation.
His “Drift” section has me confused. If someone could read what Hawks wrote, and then maybe explain the concept to me like I’m a college freshman who barely understands this stuff, that would be excellent. Basically, I don’t understand how his explanation shows that drift probably didn’t happen. Instead it seems like a lot of mathematical mumbo-jumbo, ending with Hawks stating that “contamination” might just be proof that neandertals and humans shared DNA. I’m concerned because I’m not even sure which part of it I find confusing: the concept of drift, the population genetics involved, what mtDNA tells us, or all three!
His other explanations make sense, if I assume his Drift-stuff is true. Please help!
2 thoughts on “More Neandertal mtDNA stuff…”
I think he is simply saying that it is very improbable that the single Neandertal mtDNA haplogroup “is so rare it has never been found in a sample of 100,000 people or more” (read, ‘extinct’) ENTIRELY BECAUSE OF CHANCE (sorry for the caps, I couldn’t figure out how to make the text bold).Remember that drift is a random (some people like to use big words like “stochastic”) process. What’s important is that 15/15 (100%) of the neandertal sample, covering a decent time span and geographical range, seems to share a single mtDNA haplotype. That doesn’t mean that it was the only one, and that there wasn’t maybe one haplotype more similar to modern mtDNA. But the haplotype they’ve found must have had a very high frequency. Given the population genetic parameters he describes (assumptions…), and including this haplotype as a possible ancestor of modern mtDNA haplotypes, it is incredibly improbable that the neandertal haplotype has disappeared due simply to drift, stochastic fixation/extinction. [how many times can I say ‘haplotype’?]Regarding contamination, remember that incredible steps were taken to ensure that only neandertal mtDNA was being sequenced. It is possible, then, that some modern-human-like mtDNA could have been disregarded as contamination, too human to be right. Nevertheless, given the neandertal mtDNA sample we have, it is still very unlikely that drift alone is a plausible explanation for why the haplotype is superlatively rare today.
Thanks Zach. That makes sense. I think I knew most of that, I was just having difficulties with the way Hawks put it… I think I would agree that drift is probably not the cause of the haplotype disappearing (which hopefully means I understand what I just said)On a different note: I feel like your comment, and probably Hawks’ blog should be part of a drinking game, where we drink any time the word “haplotype” is used. We’d get drunk pretty fast with posts like these!