Why it's good to be Zilhão

7 minute read

Because being at the end of the alphabet gets you the last word.

Last weekend was the new Human Revolution conference at Cambridge: "Rethinking the Human Revolution: New Behavioural & Biological Perspectives on the Origins and Dispersal of Modern Humans".

The original "Human Revolution" conference was an important moment in the development and definition of the modern human origins problem. For one of the first times, archaeologists, paleontologists, and geneticists confronted the modern human origins problem with the specter of mtDNA variation hanging over them. The meeting was held in March, 1987 at Cambridge. The papers from the conference were split into two edited volumes. The major volume from the perspective of biology is The Human Revolution: Behavioral and Biological Perspectives on the Origins of Modern Humans, edited by Paul Mellars and Chris Stringer. This volume includes 17 papers on biological change (4 genetic), and 17 on archaeology and behavior (8 theoretical, 9 regional case studies).

Some of these papers constitute the best and most accessible published statements of the authors' theoretical frameworks -- especially some that have had a more limited role in the subsequent "Neandertal-modern human" debates.

I have spoken to several of the participants in that 1987 conference, who have diverse viewpoints on the interactions and effectiveness of the conference as a whole. At the least, it can be said that the event spurred the field toward the viewpoint that modern human origins was not merely a complex problem, but an actual stumbling block to any progress in understanding the evolution of human minds (comprising culture, language, sociality, and technology). There was certainly no consensus in the field then (any more than there is today) that archaic humans were substantially or completely replaced by "modern" humans. But once that logical extreme became a possibility, the behavioral, anatomical, and genetic records could not be interpreted without reference to this phylogenetic issue. If the mode of change was replacement, there would be no sense in interpreting the evolution of Neandertals as relevant to later people. Nor could it make sense to examine the pattern of behavioral change in Africa without reference to whether that pattern led to the replacement event.

So one view is that focusing on the problem actually intensified it. But this intensification has led to productive new research in African archaeology, in genetics, and in the chronology of Late Pleistocene Europe. In all three areas, the evidence has substantially changed during the past fifteen years. The phylogenetic problem remains a stumbling block, but in a very different way.

I'm not sure you would know any of this from the current "Revolution" conference. I have received several copies (thanks, readers!) of the extended abstracts of the current conference, which were embargoed before the conference and are not to be cited without permission. But I will give some of my impressions of the composition, based on the abstracts. I apologize for not being able to do the usual cite-and-critique; what I have to offer is a fairly general overview without specifics (except in one case). I have not been successful in finding any website associated with the conference; if anyone knows of one please let me know and I'll link it.

The new "Human Revolution" conference appears to have been much less biologically-oriented than the original. By my count, only twelve papers were primarily biological in focus, and of this number only four dealt in any substantial way with fossil evidence, three were molecular (2 mtDNA, 1 Y chromosome), one was linguistic, three dealt with social evolution and the brain, and one was devoted to species concepts.

Of course, several of the papers by working archaeologists had interesting things to say about the evolution of human behavior. There were twenty-nine such papers, ranging from site reports to theoretical synopses of the origin of culture. With more talks, the archaeological side appeared to have more diversity of viewpoints -- for example Francesco d'Errico is a notable contrarian to the hypothesis that behavioral modernity had a single origin in Africa, and he was included.

On the other hand, the geographical focus of the conference increased only marginally from the earlier Human Revolution meeting. The inclusion of more work in Africa is a valued addition, and reflects the increasing focus of the field on African MSA variability. But only two papers cover the world east of the Levant, none from South Asia or China. It seems to me that if "the human revolution" is really a valid pattern, that a simple test of its validity would be a truly global comparison.

A participant would have a better impression than I do, however, and if any report to me I'll be happy to relay their views.

The genetics have a certain "fiddling while Rome burns" flavor: the three papers are attempts to further refine the chronology of the "modern human dispersal", even as evidence from the vast majority of the genome now clearly indicates a substantially different picture of modern human origins. One imagines the work of the last Ptolemaic astronomers before they heard about Kepler's ellipses.

Considering the limited program, perhaps there were not available funds to bring in more speakers on fossil humans.

But at least there was Zilhão, who with the final abstract belies much of the preceding 70 pages. He has kindly given me permission to quote his abstract (with Erik Trinkaus) here. After laying out the "lines of reasoning" underlying the "Out of Africa with Complete Replacement" model, they respond thusly:

Recent research has exposed the empirical and logical flaws that cripple these arguments:
mtDNA is but a small fraction of the total human genome; when the nuclear genome is considered (hemoglobin beta locus or, recently, the patterns of polymorphism in the RRM2P4 pseudogene), there is ample evidence of the contribution of ancient non-African, hence by definition anatomically archaic, genetic lineages to extant humanity; that extant mtDNA lineages coalesce in Africa thus probably relates to differences in the size of the Pleistocene populations of the different continents;
the level of difference in the mtDNA of Neandertals and moderns is, by Primate standards, intra-specific, not inter-specific, and extant evidence of hybridization with viable, fertile offspring between close species, and even close genus, of monkeys and baboons precludes use of taxonomic arguments to assess past population dynamics;
the absence of Neandertal lineages in the sample of the five modern humans from ca.25 ka BP whose mtDNA has reportedly been obtained is in fact consistent, depending on a number of parameters, with levels of population admixture of up to 45%, i.e., approaching panmixia;
simulation studies concluding that levels of admixture greater than 0.1% would lead to observable percentages of Neandertal mtDNA lineages in extant Europeans use unrealistic models of population interaction and in fact simply arrive at conclusions that are already contained in the premises of the model used for the simulations;
if "fully symbolic sapiens behavior" is recognized in the archeological record by artifacts or features that carry a clear, exosomatic symbolic message, such as personal ornaments, then late Neandertals exhibited fully sapiens behavior; even if resulting from long-distance diffusion, the arrival of such innovations in southwestern France many millennia before any modern humans are documented in eastern Europe carries the implication that the process operated via the exchange networks of Neandertals, i.e., that we are dealing with the spread of a concept, and that is sufficient evidence for the existence of the cognitive capabilities required for its understanding and transmission;
the marked contrast apparent in the fossil record of the late twentieth century between the "early modern" and "classical Neandertal" trait-packages, suggesting population discontinuity, was an artifact of mistaking by "early modern" specimens that, in fact, were of much later age, most from the mid/late Holocene;
all the sufficiently complete, described specimens within ca.5000 years of contact currently known and directly dated (Oase and Muierii, Romania; Mladec, Czech Republic; Lagar Velho, Portugal) feature archaic/Neandertal traits that can only be explained by admixture between modern immigrants and local autochthonous populations.


One solution to a stumbling block is to assume it doesn't exist, that people who point it out are just being obstructionists, and that no right-thinking person could seriously hold such contrarian views. That attitude allows progress of a sort -- at least in theories -- and probably makes for a more pleasant post-conference reception. This is the "holding fingers in the ears and chanting 'la, la, la'" approach.

I for one welcome the stumbling blocks. They are the ways we learn things. They are sufficient now to teach us that the "human revolution" paradigm is wrong. Whatever the mode of biological change, it was more complex than replacement. Embrace the elephant in the room.