The Peopling of the Americas III - Human Migration Rate and the possible arrival time of Anatomically Modern Humans in South America

Did Paleoamericans cross the Bering Strait 100,000 years ago? Image Credit: Adapted from LeFever 2012 (5).

In two previous posts (here and here), I examined the formation of the Bering Land Bridges. The dates generated for the existence of these Land Bridges has profound implications for the peopling of the Americas.

 I deliberately choose to cover the last 2 million years of the Pleistocene, this is essentially because the current ‘Out of Africa’ model favours 3 waves of migration:

1. Homo erectus senso lato around 2Mya.

2. Ancestors of Homo heidelbergensis and/or Homo ergastor about 0.5Mya.

3. Homo sapiens or their archaic forebears perhaps as early as 0.15Mya.

Therefore as ALL of these species have been present in East Asia over hundreds of thousands of years, it seems possible, given the opportunity presented by the Bering Land Bridges, that any, or all of them could have crossed from Asia and populated the Americas.

To decide on the who, we kind of need to know the when.

Looking on the web for difficult to answer questions can be a frustrating business for instance try “What is the earliest man could have arrived in the Americas”. The top 10 results were 16,300BP (Athena publishing), 14,500BP (Smithsonian), 15,000BP (Wikipedia), 15,500BP (Guardian), 15,000BP (Daily Mail), 13,300BP (PBS Newshour), 14,000BP (Nature), 12,000BP (National Geographic), 22,000BP (New York Times) and 16,500BP (Centre for the First Americas). The average date is therefore about 15,400BP. This is despite the fact that Dillehay (4) recently published a paper stating that the Monte Verde site near the southern tip of Chile was occupied by 18,500BP.

I find this deeply frustrating. With very little effort one can find NUMEROUS sites that have good evidence that pre-date these stated dates by a WIDE margin.

Current evidence of man in the Americas can be summarised in the following table:

 

 

 

If we assume that these dates are correct, could anatomically modern humans account for these occupations?

To decide whether the full range of occupation dates listed above, can be accounted for by Anatomically Modern Humans (AMH) we therefore need some estimate of the rate of Human Migration. I could at this point try to refer you to a range of estimates from learned papers on the internet, however these are even more sparse and contradictory than dates for the first peopling of the Americas as outlined above.

Therefore I have carried out a simple calculation based on some of the published, dated fossils from along man’s migration route.

 

Taking the fastest migration rate of 0.27Km/year we can do a simple calculation about the arrival time at Monte Verde in southern Chile:
 

Wales Alaska to Monte Verde Chile = ca. 14726km

Migration time 14726/0.27 = 54540 years
 

Therefore arrival time in southern Chile would be 94400-54540 = 39860 years BP
 

Conclusions:
 

1. Anatomically modern humans could have arrived in Beringia ca. 100,000 years ago.
 

2. Given a migration rate of 0.27Km/year all sites in the Americas, with the exception of Valsequillo and Calico could have, therefore, potentially been occupied by Anatomically Modern Humans (AMHs).
 

3. Arguments regarding the opening and shutting of the Ice-Free corridor are irrelevant as land-based migrations could have taken place BEFORE it closed. Coastal migrations are not ruled out.

4. A quick check against my previous post here shows that  Bering Land Bridge 4 96-93 Kya, 5 104-102 Kya and 6 114.5-111.5 Kya existed at approximately the right time for this human migration.
 

5. Valsequillo and Calico, if real sites of human occupation MUST, therefore represent an archaic human population such as Homo erectus.

 

References

1. Ian McDougall, Francis H. Brown & John G. Fleagle.2005. Stratigraphic placement and age of modern humans from Kibish, Ethiopia. Nature 433, 733-736 doi:10.1038/nature03258

2. R. Grun et al. 2005. U-series and ESR analyses of bones and teeth relating to the human burials from Skhul. Journal of Human Evolution 49 316-334

3. Wu Liu, et. al. 2015. The earliest unequivocally modern humans in southern China. Nature  526, 696–699. doi:10.1038/nature15696

4. Dillehay TD, Ocampo C, Saavedra J, Sawakuchi AO, Vega RM, Pino M, et al. (2015) New Archaeological Evidence for an Early Human Presence at Monte Verde, Chile. PLoS ONE 10(11): e0141923. doi:10.1371/journal.pone.0141923

5. Greg LeFever Ancient Tides blog 2012. Retrieved from:

http://ancient-tides.blogspot.co.uk/2012/12/native-american-genetic-source-is.html