… But Most of Us Are a Little
by Aaron Jonas Stutz
Every single one of us on Earth today is, by definition, an anatomically modern human. We differ a lot from the Neandertal anatomical pattern that–despite variations among individuals–generally prevailed across western Eurasia some 50,000 years ago. It stands to reason that it would have taken some time for evolution to have shaped the anatomical features that we all now share. It’s reasonable to expect that, going back well into the last Ice Age–which ended 12,000 or so years ago–our ancestors would have also been anatomically modern human, not Neandertal.
The fossil record suggests that the founding anatomically modern human populations were distributed through Africa, extending into the Levant, just outside of Africa, all between 200-100 thousand years ago (see Wolpoff & Lee, 2012, for a scholarly discussion). But bits of intact DNA extracted from ancient Neandertal and anatomically modern human bones alike confirm–with remarkable specifics –what some paleoanthropologists have generally been arguing for decades (Thorne & Wolpoff, 1992). Our ancestry isn’t so simple.
The Complex Evolutionary Roots of “Anatomical Modernity”: The Neandertal Contribution
Except for people in most Subsaharan African populations, everyone else living today has the same amount of DNA from really ancient Neandertal ancestors as we each inherit from one great-great-great-great or great-great-great-great-great grandparent (around 1% of our six billion or so diploid nuclear DNA base pairs, sprinkled at different locations across each chromosome in the set of 23 each we inherit from mom and dad; Fu et al., 2014; Green et al., 2010; Lazaridis et al., 2014; Sankararaman et al., 2014).
While some contemporary African populations exhibit this low but significant level of Neandertal ancestry, most do not have any measurable Neandertal genetic background. Still, that means the vast majority of people alive today, spanning pretty much every single continent and major island that humans inhabit, have the equivalent of a quite recent ancestor’s worth of Neandertal DNA.
Now, none of our great-great-great-great-great grandparents–we each have 128 of them if there hasn’t been any recent cousin-marriage in our genealogy–were Neandertals. (We’re talking technically. No joking about Neandertals in this post. Nor about cousin marriage. Which isn’t just for Neandertals [see Prüfer et al., 2013]. It’s more common than you think. It’s even prestigious in many historical and contemporary cultural contexts, with no “ewww” factor at all. And until recently, the social benefits seem to have outweighed the costs of inbreeding depression, because endogamous clans often had higher fertility [Bittles et al., 2002]. Only a Neandertal would have a such low-brow, knee-jerk sense of humor to take such things as a joke… hmmm…) So, most of us have a recent-ancestor-like contribution of Neandertal genes in each cell in our body. In fact, we’ve inherited these Neandertal DNA markers from both mom and dad, who inherited them from our grandparents, etc.
Indeed, no Neandertals existed to marry into the family two hundred years ago. How, then, how did so many people on Earth today get all of these distinctive Neandertal DNA markers? This question is the most scientifically compelling reason why our Neandertal ancestry matters. It’s one of those captivating scientific puzzles. It’s just not at all obvious how such small fragments of Neandertal DNA–with loci here and loci there sprinkled across our 23 pairs of chromosomes–have persisted in human populations that have now spread around the world. Neandertal DNA variants haven’t disappeared through random genetic drift in populations otherwise mainly descended from Neandertals. They’ve instead stayed around for tens of thousands of years–that’s something approaching 1500 generations–long after Neandertal anatomical patterns went extinct.
So, What Does Shared Neandertal Ancestry Have to Do With the Protoaurignacian?
A recent report from a genomics conference has just brought all of this Neandertal genomics research back to our attention (Callaway, 2015; Gibbons, 2015), with confirmation that some roughly 40,000-year-old European fossils with anatomically modern features also preserve substantial bits of Neandertal DNA (see also Fu et al., 2014). Here, the latest Neandertal genomics findings sheds critical light on another recent research report. This one is archaeological. It claims that the so-called Protoaurignacian–which is an archaeological culture consisting of stone and bone tool patterns found in association in numerous southern and western European sites, dating to the Early Upper Paleolithic–“triggered the demise of the Neandertals in this area” (Benazzi et al., 2015).
The problem is, the Protoaurignacian couldn’t have triggered anything…
… let alone triggered the “demise” of Neandertal anatomical patterns, while allowing enough Neandertal-anatomically modern human admixture to shape an interesting little bit of our genetics, right up to the present day.
That seems to be a more complicated biocultural evolutionary development.
The following two posts will delve into what we’re learning about the complex relationships–or sometimes, lack of them–among anatomical change, genetic change, and technological change in the emergence of the Protoaurignacian technological systems across much of western Eurasia … just as anatomical modern human-Neandertal population biological turnover was under way.
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Bittles, A. H., Grant, J. C., Sullivan, S. G., & Hussain, R. (2002). Does inbreeding lead to decreased human fertility? Annals of Human Biology, 29(2), 111–130. http://doi.org/10.1080/03014460110075657
Callaway, E. (2015). Early European may have had Neanderthal great-great-grandparent. Nature. http://doi.org/10.1038/nature.2015.17534
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Sankararaman, S., Mallick, S., Dannemann, M., Prüfer, K., Kelso, J., Pääbo, S., … Reich, D. (2014). The genomic landscape of Neanderthal ancestry in present-day humans. Nature, 507(7492), 354–357. http://doi.org/10.1038/nature12961
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