Human Phylogeography

February 23, 2019 • 11:33 am

by Greg Mayer

For the spring semester, my colleague Dave Rogers and I are teaching a seminar class entitled “Human Phylogeography.” Phylogeography is the study of the history of the genetic variation, and of genetic lineages, within a species (or closely related group of species), and in the seminar we are looking at the phylogeography of human populations. DNA sequencing now allows a fine scale mapping of the distribution of genetic variation within and among populations, and, remarkably, the ability to sequence ancient DNA from fossil remains (including Neanderthals). The seminar is based primarily on a close reading of David Reich’s (2018) Who We Are and How We Got Here (published by OUP in the UK).

A Krapina, Croatia, Neanderthal woman, photo by Jerry.

Although rarely under that rubric, human phylogeography has been a frequent topic of discussion here at WEIT, by Jerry, Matthew, and myself, including our several discussions of Neanderthals (or Neandertals) and Denisovans. So it may be of interest for WEIT readers to follow along. Below the fold I’ve placed the course syllabus, which includes the readings, and links to many newspaper articles of interest, and online postings, including many here at WEIT, and also from John Hawks Weblog, a site we’ve recommended on a number of occasions when discussing human evolution. (The newspaper links appear as images; just click to go to the story.) We just finished our third meeting, and I’ve been quite impressed by the students’ discussion and writing. We’re fortunate to have some students from anthropology or with some anthro background.

Please read along with us, or browse what seems interesting below. If you have questions or comments, post them here, and I’ll be looking in.

Continue reading “Human Phylogeography”

Svante Pääbo gives a good public lecture on Neanderthals, Denisovans, and other relatives of modern humans

October 26, 2018 • 12:30 pm

I think most readers know about Svante Pääbo and his work on “paleoanthropology”: the study of the evolution and ancient movements of H. sapiens through analysis of “fossil DNA”.  His most famous work is on the genetics of Neanderthals, a subject in which I’ve recently become interested.

Pääbo’s work been extended to Denisovans and other previously unknown human groups, and what we’re learning is that even in H. sapiens the evolutionary tree is convoluted and interconnected. This does not, by the way, vindicate the thesis that evolutionary trees are wrong, or can’t be accurately determined. Despite that, there are some fossil individuals so genetically heterogeneous that they can’t be slotted into one group or another (see below). Our relatives were “mixing” quite promiscuously when they met.

In this remarkably clear lecture (h/t: Matthew Cobb), which proceeds chronologically through the scientific findings, Pääbo lays out the genetic data produced by his lab. (This is the award lecture accompanying Pääbo’s 2018 Nierenberg Award for Science in the Public Interest, given on October 3 of this year.)  There’s some freaky stuff in here, including an individual that appears to be an F1 (first-generation) hybrid between a Neanderthal and a Denisovan (about 32 minutes in).

36 minutes into the lecture, Pääbo summaries the contribution of Neanderthal and Denisovan genes to modern humans, including the possibility that a gene we carry from Neanderthals that now gives us a higher propensity for type 2 diabetes could have been an allele that helped Neanderthals deal with starvation. Similarly, Denisovans have bequeathed to modern Tibetan populations a gene that helps deal with high altitude.

In fact, there are at least a dozen “archaic” genes from Neanderthals and Denisovans that remain in our genomes and are associated with disease, perhaps because they don’t function well in the genetic backgrounds of modern humans. (There’s evidence that some of these have been selected against.) At the end, Pääbo discusses the genes in modern humans not present in Denisovans or Neanderthals; the idea here are that these human-specific genes (there are 87) that makes us “important” and “special”. I’ll let you watch those last 12 minutes on your own. There are four minutes of questions at the end.

All in all, this is a superb introduction to the complex and always-changing picture of our relationship to recent hominin relatives. If you watch it, and you should, you’ll be absolutely up to speed on human paleogenetics. But, as Steve Gould used to say, when he lectured on human evolution at Harvard each year, his first act was to throw out all his notes from the previous year’s lecture.