Hominin increase in cranial capacity, courtesy of Luke Jostins
A few years ago a statistical geneticist at Cambridge’s Sanger Institute, Luke Jostins, posted the chart above using data from fossils on cranial capacity of hominins (the human lineage). As you can see there was a gradual increase in cranial capacity until ~250,000 years before the present, and then a more rapid increase. I should also note that from what I know about the empirical data, mean human cranial capacity peaked around the Last Glacial Maximum. Our brains have been shrinking, even relative to our body sizes (we’re not as large as we were during the Ice Age). But that’s neither here nor there. In the comments Jostins observes:
The data above includes all known Homo skulls, but none of the results change if you exclude the 24 Neandertals. In fact, you see the same results if you exclude Sapiens but keep Neandertals; the trends are pan-Homo, and aren’t confined to a specific lineage….
Interesting piece in LiveScience, What We Learned About Our Human Ancestors in 2011. The author highlights the likelihood of a lot of admixture across very diverged lineages, as well as the nascent “Out of Arabia” hypothesis. This quote from Michael Hammer gets at where we’re “going next”:
“We’ve probably just scratched the surface of what we might find,” Hammer added. “We only looked at a small number of regions of the genome. This coming year, you’ll see a lot of progress made with full genome data. This year, we should be able to confirm what we found and go way beyond that.”
I think the the lowest hanging fruit in terms of “paradigm shift” was the renewed opening to admixture with “archaic” lineages in 2010 and 2011. Before that point it was reasonable for anyone to respond to these hypotheses with a recitation of the “Out of Africa” orthodoxy. Now no longer. If admixture did no occur, then we’re talking about strange results which still need explaining with a novel model (e.g., lots of “structure” in the “Out of Africa” population due to admixture within Africa). But as the low hanging fruit is picked, researchers are now going to spread themselves out throughout the grove, hunting for numerous odds and ends. In all likelihood the picture is going to get complex, but hopefully it will be more accurate.
The Pith: I review a recent paper which argues for a southern African origin of modern humanity. I argue that the statistical inference shouldn’t be trusted as the final word. This paper reinforces previously known facts, but does not add much that both novel and robust.
I have now read the paper which I expressed a touch of skepticism toward yesterday. Do note, I did not dispute the validity of their results. They seem eminently plausible. I was simply skeptical that we could, with any level of robustness, claim that anatomically modern humans arose in southern vs. eastern, or western, Africa. If I had to bet, my rank order would be southern ~ eastern > western. But my confidence in my assessment is very low.
First things first. You should read the whole paper, since someone paid for it to be open access. Second, much props to whoever decided to put their original SNP data online. I’ve already pulled it down, and sent off emails to Zack, David, and Dienekes. There are some northern African populations which allow us to expand beyond the Mozabites, though unfortunately there are only 55,000 SNPs in that case (I haven’t merged the data, so I don’t know how much will remain after combining with HapMap or HGDP data set).