An introduction to and anatomical evidence supporting Neandertal introgression (Part 1)

PNAS has released a one-two sucker punch of information regarding Neandertal and human evolution. The first piece of information came from an anatomical and carbon dating reanalysis of ‘early modern humans’ from Pestera Muierii. Erik Trinkaus conducted this research, and here is the DOI link to the paper. The second piece of information comes from Bruce Lahn’s lab at Howard Hughes Medical Institute, and that paper is titled, “Evidence that the adaptive allele of the brain size gene microcephalin introgressed into Homo sapiens from an archaic Homo lineage.” This just came out this week and it supplements the previous anatomical analysis with comparative genomic analysis.

Before I get into the details, as you may know I haven’t yet commented on this all. Instead, I’ve taken a step back, this week or so, to watch everyone blog about it and throw in their two cents, because these two papers really change a lot. I guess you can say it all started in May-July of this year, when Razib commented or rather schooled me on what Bruce Lahn now knows… actually if you trace back all the posts and what not, I must have been oblivious to not see this coming. In my post, I wondered if Lahn had not read Paabo’s PLoS paper, “No Evidence of Neandertal mtDNA Contribution to Early Modern Humans?” Razib told me,

“Lahn knows about the mtDNA work of Paabo, but, he has information about other loci that you do not.”

Since then, one of the crutches behind my argument and pretty much a lot of other people who were taught that Neandertals did not significant contribute to the evolution of modern humans, has been invalidated. mtDNA, the line of evidence to ‘seal the deal’ (at the time), that humans and Neandertals completely diverged roughly 400,000 years ago is now in jeopardy thanks to RPM of evolgen. He shared with us, African-American mitochondrial DNAs often match mtDNAs found in multiple African ethnic groups. I won’t get in the details of this invalidation, but take my word for it… The paper effectively nailed anyone for relying on mtDNA as a single line of evidence to make difinitive conclusions.

The Anatomical Evidence

Okay, so now that I’ve basically established almost everything I knew and have been taught about Neandertals and humans to be wrong, let’s fast forward to 10 days ago. Trinkaus’ and his colleagues, Soficaru and Dobos, published that anatomical reanalysis of the remains from Pester Muierii, that I mentioned above. In the paper they outline that the potential information the fossils from Pestera Muierii could provide has been really neglected in the last 50 or so years since they were dug up. The preliminary dating lead to a lot of confusion, and because of that the ‘fossils have never been integrated into paleoanthropology.’ And because there has been ‘accumulating evidence that… present[s] a variable mosaic of derived modern, archaic human, and Neandertal features,’ Soficaru, et al. turned to the Pestera Muierii fossils since they hadn’t been really analyzed.

First, Soficaru, Dobos, and Trinkaus re-carbon dated the bones. The previous carbon dating that lead to a lot of confusion was flawed because it used a mixture of samples from various bones that were most likely not from the same individual. Instead Soficaru et al. took small samples from each bone. The resulting dates were consistent to be around ~ 30 ka, and lead the authors to conclude they were probably derived from a single phase of occupation of the Pestera Muierii cave.

That being said, the morphology of the Muierii fossils was analyzed. What they had in front of them was a cranium, mandible, scapula, tibia, temporal, and fibula bones… to which they can attribute only three individuals. They made some outstanding conclusions, after comparative anatomical analyis, that these fossils have traits seen in Neandertal and human bones. For example, the occipital bun in Muierii individual 1 is very pronounced, and that is consistent in most Neandertals, and very infrequent in other species. I’ve included an image (figure 1), with an arrow to the bun. And for your own comparative test, follow the advice from this thread, feel the back bottom of your own head. You shouldn’t feel a bump as big as Muierii 1 has, it’s massive there.

Lateral view of the Muierii 1 cranium

Fig. 1.Lateral view of the Muierii 1 cranium. Note the massive occipital bun, identified by the red arrow. (Scale bar: centimeters.)

Muierii 1 also lacks an external occipital protuberance, a little bump seen on the occipital bone. This occipital protuberance is present in the skulls from modern day Asian populations as well as early human ancestors; but all Neandertals (expect two from Asia, not surprisingly) do not have this protuberance. I’ll stop here with the anatomical evidence but let’s recap on the conclusions. Trinkaus and crew re-dated Pestera Muierii fossil remains to fall in the Upper Paleolithic. The remains also show a ‘morphological mosiac’ of traits seen in both Neandertals and Homo sapien fossil specimens. This falls in with conclusions made by Vallois (1958); Trinkaus, et al. (2003); Trinkaus, et al. (2006); Frayer, et al.(in press); Wolpoff, et al. (2006), and Trinkaus (2005).

Now that we have anatomical evidence that establishes an admixture of Homo sapiens features in Neandertal bones, we should be asking, “Did humans and Neandertals get it on?” Bones can only tell us so much, they are merely phenotypes that are heavily variable and affected by environment, lifestyle and life history, as I outlined in bone is a dynamic tissue, remodeling with time and life. The only way to say for sure is to show some sort of recombination of DNA; i.e. some from Neandertals in modern humans… and that’s where I’ll leave you guys off at. I resume the second half of this post on Thursday.

6 thoughts on “An introduction to and anatomical evidence supporting Neandertal introgression (Part 1)

  1. can you please give out clearly summary of what have been discusded above so that yhe learner could understand.also provide some question

  2. I have an external occipital protuberance on the magnitude of about 4+.. and I do not show any asian traits or lineage that I know of. What is the possibility that this is an evolutionary feature? :)

  3. I was recently studying a book called “Atlas for Human Anatomy for the Artist” by Stephen Peck. While reading the section on the human skull, it sparked my interest to do some research on why my occipital protuberance is rather morphed compared to the “normal” human skull. My occipital protuberance is a quarter the height of the pic shown here and juts out about 1/2 an inch. It is a very pronounced “ridge” that is very noticeable when I cut my hair very short. My heritage is french/irish. When asked why my head is so large (such as when trying on hats), I proclaim that I am a mutant that has an enlarged “cranial ridge” that protects my visual cortex in case of a surprise attack from behind.

    1. same also irish/scot/french head hat size only 7 1/8 tho but have a huge occipital protuberance in comparison.

  4. Hello. I am writing a paper on the evolution of humans and the hybridisation between ‘Moderns’ and Neanderthals. The evidence seems pretty convincing. The documant is to be edited shortly. If anyone is interested – please let me know.

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