It was my first semester of graduate school, fall of 2001. I was in a seminar class on paleoethnobotany, the study of ancient human-plant interactions, taught by Deborah Pearsall, who later become one of my doctoral advisors. In the ground floor meeting room of Swallow Hall, a small group and I were discussing what we read on the peopling of the Americas. What do we know for sure about the first Native Americans? We brought up key sites like Monte Verde and the evidence for different paths that people could have used at different times. There were a lot of data to explore, but they did not seem to form a consensus. Dr. Pearsall rephrased the topic to keep the talk going: what would you tell a class of undergraduate students about what we know about the peopling of the Americas?
â€œWe donâ€™t really know anything for certain,â€ I answered. Amused, Dr. Pearsall pushed for more: â€œWell you have to tell them something.â€
Summer of 2018. I was now far from graduate school and writing a textbook chapter on modern human origins. I covered key evidence of an African origin and expansion through the Middle East, across Asia, and to Australia. The next section was about the peopling of the Americas.
I have to tell them something.
Seventeen years after that seminar, research on the peopling of the Americas has filled in some details, but unanswered questions and competing theories still exist. Back then, the Ice-Free Corridor was the strongest theory. ItÂ stated that Asians crossed the land bridge of Beringia inland between two glaciers. One conflicting piece of evidence came from the Chilean site of Monte Verde, which was dated too early for the Ice-Free Corridor theory to work barring a full spring from Alaska to Chile. The date of Monte Verde was just confirmed a few years before the seminar, so researchers were just starting to take the implications of that site seriously. I did not keep up with developments until recently when I started teaching my own introductory course. That was when I started hearing more about the Coastal Migration theory, that people expanded along the coast of Beringia before the inland route was available. I was skeptical at first since I was already settled on the Ice-Free corridor. As I read recent papers, though, I became increasingly convinced. Tracing the coasts was a common theme in modern human expansion. Evidence of this pattern appears in all of the continents. The growing collection of early sites in the Americas weakened the Ice Free Corridor theory but was compatible with Coastal Migration. While there was no absolute direct evidence for expansion along the coast, there was no absolutely contradictory evidence either.
I finally knew what to say to students about the peopling of the Americas. I touched on the transition between models and the accumulating evidence for Coastal Migration. Satisfied that I had done that topic justice, I moved on to other sections in my chapter.
The day before my textbook draft was due, a new article came out stating that both major theories are still viable given the evidence (Potter et al. 2018). (A between-the-lines reading of the article is that it greatly supports the Ice Free Corridor over Coastal Migration). The article was not enough to bring me back to the Ice Free Corridor, though, especially as the earlier of the two options. Still, given this new publication I decided that I should adjust my section since it reminded me that the issue was not settled.
After so many years, I thought archaeology had finally arrived at a single explanation of the peopling of the Americas and I was ready to bring upcoming students the news. Perhaps I was too optimistic. Unlike other introductory science classes, the fundamentals of biological anthropology change rapidly and textbook authors have to work with that. Maybe we still donâ€™t really know anything for certain, but I know more about what to tell students. I show them the current state of research and own summary of it, andÂ let students go from there.
Potter, B. A., Baichtal, J. F., Beaudoin, A. B., Fehren-Schmitz, L., Haynes, C. V., Holliday, V. T.,Â .Â .Â .Â Surovell, T. A. (2018). Current evidence allows multiple models for the peopling of the Americas. Sci Adv, 4(8), eaat5473. doi:10.1126/sciadv.aat5473