An article published in late August in the online journal Current Biology sparked a flurry of popular science articles—National Geographic, Live Science, BBC News—that reported early modern humans were responsible for nearly wiping out a newly discovered species of giant clam, T. costata, 125,000 years ago. The proposed implication of this is that the over-harvesting of T. costata may have also spurred early modern humans to leave Africa. Although I didn’t have access to the original article in Current Biology, from the response articles I gathered that the evidence used to support the idea of human over-harvesting of the giant clams was solely the diminishing population size and shell size of the clam coinciding with the hypothesized date that Anatomically Modern Homo Sapiens Sapiens (AMHSS) left Africa. Of course the popular science articles might be magnifying the focus on humans for their own audiences. The original article was, after all, published in a biology journal.
If the hypothesis being circulated, that early modern humans are responsible for the near extinction of T. costata, it will have some profound implications for the field of anthropology. I’m hesitant to easily accept this explanation for several reasons. Judging from the evidence presented by the popular science articles, the focus of their research was the biology and near extinction of T. costata. There are potentially dozens of explanations for why a species’ population size might suddenly diminish. There also seems to be very little interdisciplinary collaboration on this research topic; all of the researchers involved are in the marine biology field with an emphasis on coral reef ecology. This is a perfect research question to warrant an interdisciplinary approach. Finally, the actual date and route of AMHSS out of Africa is still highly debated in the academic world – suggested dates range from 50 kya to 200 kya, not to mention all the different theories in circulation about the spread of AMHSS across the earth. Talk about a can of worms! I’ll briefly go over the different theories in this post and go more in depth in a future one.
An argument involving the subsistence of AMHSS is by nature an interdisciplinary one. At the very least it involves archaeologist, paleoecologists, paleobiologists, and possibly geologists. The article in Current Biology does not seem to involve such an interdisciplinary approach. All of the listed authors have a focus on coral reef ecology. Admittedly, this might be all they need for the real focus of the article: the biology of T. costata. Whether or not those authors intended to raise the issue of early modern humans over harvesting giant clams the popular science articles certainly brought it up in a light that would benefit from interdisciplinary collaboration.
The need for interdisciplinary cooperation on this subject gets me to my next point – that there are potentially dozens of reasons that T. costata nearly disappeared. Paleoecologists would be able to help determine what the environmental conditions were at the time. A slight shift in the climate or chemistry of the marine environment could be disastrous for certain marine species. Paleobiologists and marine biologists together might be able to determine what other marine life existed at the time. Is it possible that T. costata had another predator at the time besides humans? Aside from other marine predators there were still other hominids running around 125,000 years ago. This is a possibility that professor John Hawks talks about on his blog. The process of natural selection would suggest that if a species were being selected for its nutritional value then the larger specimens would be hunted first and thus removed from the gene pool resulting in the decrease in shell size that was noted in the original article. Archaeologists would also be of use to identify evidence of humans harvesting T. costata in archaeological assemblages from the area in the period in question. We have no way of knowing for sure until we investigate other explanations or look for further evidence to support the hypothesis.
Uff da! (As we say here at Luther College). Now we’re left with the debate about the nature of AMHSS movement out of Africa. However, the Multiregional Continuity Theory contests even the hypothesis that AMHSS developed in Africa. Historically the Out of Africa hypothesis has been more popular among scholars. The theory is further differentiated into two separate iterations – the Recent Migration Theory and the Multiple Dispersal Model. Both of these present different hypotheses of how and where humans moved off the African continent. Both use genetic evidence alongside archaeological and anatomical data. The dates for all of these differing theories place the migration of AMHSS out of Africa from 50,000 to 200,000 years ago. This is a huge range! The most widely accepted average is between 100,000 and 60,000 years ago with more evidence indicating that the actual date is closer to 100,000 years ago. Does this mean that it’s possible that the near extinction of giant clams influenced AMHSS’s move from Africa? Sure it’s possible, but not all the evidence is in and the jury has yet to reach a verdict.
It would certainly be an interesting development for the field of anthropology if this newly discovered species of giant clam did indeed contribute to AMHSS moving out of Africa. I think we need to use a certain amount of caution in determining whether or not to believe this claim without multiple lines of evidence and interdisciplinary cooperation. In any field of science we progress in our understanding of the world by sharply questioning everything – so that is exactly what I think we ought to do in this case.
If you are interested in reading more about this topic or any of the points I raised here are some links I found helpful:
NERC: Africa-Arabia connections: coastal environments, tectonics and human dispersals - http://www.nerc.ac.uk/research/programmes/efched/results/bailey.asp
Bradshaw Foundation: Journey of Mankind - http://www.bradshawfoundation.com/stephenoppenheimer/
Action bioscience: Origins of Modern Humans – http://www.actionbioscience.org/evolution/johanson.html
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