As I mentioned the other day, there was an interesting exchange in PNAS concerning the impact hypothesis. The cause of the exchange was an article published in PNAS back in August.
One of the predictions of the impact hypothesis is that there was a major decline in Paleoindian populations (i. e. Clovis, any mention of which causes emotions to run high). So, the question is, how does one get an estimate of population size before and after the presumed impact? One way is to use radiocarbon dates as a proxy. Basically, a summed probability distribution is created of, in this case 1,509 RC dates from sites in Canada and the US (dates range from 13,000 to 8,000 14C BP). Population increases and decreases are represented as peaks and troughs, respectively, in the distribution. The technique has been used in Europe and seems promising. Buchanan, Collard, and Edinborough argue that based on their analysis the impact hypothesis is not supported by their data. Five of the six letters in PNAS attack Buchanan et al’s paper, mainly on the grounds of geographic spread of the dates and data quality (too few dates, large error margins, etc.). The sixth paper is Buchanan et al’s response. Unfortunately, I don’t have that, so I can’t say who got the better of the exchange…
Filed under: Archaeology |
Afarensis: Anthropology, Evolution, and Science 
I just tried to get the response, and it’s available “to maintenance users only”. Carrying a screwdriver doesn’t work.
Has anyone tried to use genetics to look for a collapse in the populations? I don’t know enough about the demography, but there are genetic tools which might pick this up, with a suitably closed population and lots of genotyping.
Sadly, my mad hacker skilz make kindergartners laugh and point derisively, so I haven’t been able to read any of the exchange. If any one is able to put it all together, I’d love to read it.
I’ve emailed you a copy.
John – I sent them to you, let me know if they didn’t arrive.
Bob – Most of the studies I am aware of look at when Native American and Asian populations split, and hence, at when people first arrived in the Americas. This study in PLoS being a good example (note this study seems to show a decrease in in effective population size around 15,000-10,000 years ago – which is attributed to the re-inundation of Beringia and the resulting cessation of migration).