Riparo Mezzena and the Neandertal transition

A paper by Silvana Condemi and colleagues examines the anatomy of a partial mandible from Riparo Mezzena, Italy Condemi:Mezzena:2013. The mandible is a relatively late Neandertal specimen by its archaeological association and mtDNA sequence. As the introduction to the paper notes, the identities of skeletal specimens in the timespan from 45,000 to 30,000 years ago across Europe have been shifting along with radiocarbon ages and further analyses of fragmentary specimens. In this case, like other late Neandertals, the specimen bears a chin:

This study of the Mezzena mandible shows that the chin region is similar to that of other late Neanderthals which display a much more modern morphology with an incipient mental trigone (e.g. Spy 1, Saint Csaire). In our view, this change in morphology among late Neanderthals reopens the debate on the "more modern like" morphology of late Neanderthals and can lend support to the hypothesis of a certain degree of continuity with AMHs or a possible interbreeding with them.

The paper concludes that the Mezzena mandible lies morphologically amid the sample of modern humans from Upper Paleolithic and Levantine Middle Paleolithic contexts, even when compared to Neandertals like Saint Césaire or La Ferrassie 1 that have relatively vertical mandibular symphyses.

I prefer not to play the game, “is it a Neandertal?”, “is it a modern human?” If we had a sample of well-dated relatively complete specimens across the period from 45,000 to 30,000 years ago, we could test the hypothesis that two populations (earlier Neandertals and later “modern” humans) were genetically well-differentiated from each other. We don’t have that sample.

In my view, we shouldn’t assume more than we know, which is that both the frequencies and combination of traits of earlier Neandertals are much more strongly present in Mousterian-associated specimens than in other, mostly later, industries. I don’t yet see a reason to exclude the hypothesis that this pattern reflects both evolution and migration into Europe. And as I wrote last year, the late Neandertals may represent both evolution and migration into Europe from a central Asian or West Asian source population Hawks:dynamics:2012.

One effect of genetic sequences has been to demonstrate that anthropologists’ morphological distinctions among Neandertals don’t match the groupings we would make along purely genetic lines. I considered this problem in my paper last year, “Dynamics of genetic and morphological variability within Neandertals” (open access, PDF) Hawks:dynamics:2012. Jim Ahern and colleagues (including me) have showed that the Vindija G3 Neandertals have morphological features that are not typical of classic Neandertals, and that are significantly different in the modern human direction Ahern:Vindija:2002, Ahern:2004. Here’s what I wrote last year:

The discussion of genetic diversity among these Neandertals has not yet attempted to reconcile their genealogical arrangement with morphological classification schemes. The later Western European Neandertals that share a close mtDNA genealogical connection (Vindija-Feldhofer-El Sidrn) are not synonymous with "classic Neandertals". The well-known classic Neandertals include specimens such as La Chapelle-aux-Saints (France), La Ferrassie 1, Monte Circeo 1 (Guattari) as well as Feldhofer 1. This classic Neandertal sample includes specimens earlier than 70,000 years old and some as recent as 45,000 years ago. The classic Neandertals flank both the earlier and later sides of the 50,000-year-ago dispersal of Neandertals proposed by Dalen and colleagues (Dalen et al., 2012).

Meanwhile, the clade that connects late European Neandertal mtDNA into a tight cluster includes great morphological diversity. The two Vindija mtDNA sequences included by Daln and colleagues (Dalen et al., 2012) are both from layer G3 of the site, perhaps 40,000 years old. Both are derived from postcranial fragments without diagnostic morphological traits. The other material from G3 includes cranial, mandibular and dental remains that are not synonymous with classic Neandertal morphology (Ahern, 2004). These late Neandertals from Vindija display less pronounced morphology than classic Neandertals and lack traits that are common in the earlier classic Neandertals (Smith, 1992). These specimens are connected to Feldhofer and El Sidrn not only by mtDNA relationships but also their very low nuclear DNA diversification. If the Vindija specimens can be lumped together in mtDNA and nuclear DNA diversity with the remains from El Sidrn and Feldhofer, it seems possible that traditional morphological groupings will fail to capture real biological differences among Neandertal populations.

Riparo Mezzena adds further to this pattern. I would note that this looks at the moment like the specimen most likely to give rise to an Italian Neandertal whole genome. As we begin to examine the data from the Denisova Neandertal specimen (“A new high-coverage Neandertal genome”), the population genetics of later Neandertals will come more and more into focus.

Steven Churchill and Fred Smith wrote a review of the initial Upper Paleolithic skeletal record several years ago Churchill:Smith:2000 that still remains the best single summary of the remains from this time period. What strikes you in this review is the overall fragmentary nature of the record. That review is already out of date in some respects, as a number of specimens have been moved into or out of this period by radiocarbon revisions, and the archaeological conception of “early Aurignacian” has substantially changed.

There really ought to be an equivalent review for the latest Neandertals. I think that the sample has become more complex and confusing as we have developed a better idea of the genetics.