Saturday, 25 October 2014

Rapid Human Evolution In South America

The Cuncaicha rock shelter, high in the Peruvian Andes
Photo: Barbara Fraser
Humans were living at extreme altitudes 1000 years earlier than thought | Science/AAAS | News

A paper published a few days ago suggests human evolution, under the right conditions, can be very rapid.

A mixed American, German and Canadian team led by Kurt Rademaker of Department of Anthropology, University of Maine, Orono, ME, USA have discovered that humans lived above 4300 metres for at least part of the year, probably as seasonal hunters, in the High Andes within 2000 years of settling at Monte Verde in Chile. Monte Verde, at about 14,000 BCE is the earliest widely accepted site for human occupation in South America by Paleoindians, although a claim has been made for a 20,000 BCE site at Toca da Tira Peia in Northern Brazil.

Study of human adaptation to extreme environments is important for understanding our cultural and genetic capacity for survival. The Pucuncho Basin in the southern Peruvian Andes contains the highest-altitude Pleistocene archaeological sites yet identified in the world, about 900 meters above confidently dated contemporary sites. The Pucuncho workshop site [4355 meters above sea level (masl)] includes two fishtail projectile points, which date to about 12.8 to 11.5 thousand years ago (ka). Cuncaicha rock shelter (4480 masl) has a robust, well-preserved, and well-dated occupation sequence spanning the past 12.4 thousand years (ky), with 21 dates older than 11.5 ka. Our results demonstrate that despite cold temperatures and low-oxygen conditions, hunter-gatherers colonized extreme high-altitude Andean environments in the Terminal Pleistocene, within about 2 ky of the initial entry of humans to South America.

The team found hundreds of stone tools in the Pucuncho Basin in the southern Peruvian Andes and in the Cuncaicha rock shelter they found rock art, soot from campfires, the remains of plants found only at lower altitudes and the bones of vicuña, and guanaco (relatives of llamas and alpacas) as well as taruka deer.

Carbon dating by three different radiocarbon labs all agreed on a date around 12,00 - 12,400 for the rock shelter specimens. This location is also the source of obsidian, used for stone tools. It seems highly likely that groups of specialist hunters travelled up to this site to gather obsidian and make tools. They took staple plant food with them and hunted local game for food and possibly to take back down to the coastal settlements.

The significance of this discovery is that it is so high and so soon after humans first arrived in South America. Humans normally find it difficult to survive for very long at altitudes above about 2,500 metres because of the low partial pressure of oxygen at that altitude. Additionally, the thin atmosphere is a poor barrier to harmful solar radiation and the temperature plummets at night because there is little insulation. Yet this Andean site is more than 1,800 metres above this normal upper limit.

To live and work at that altitude for any length of time would have been almost impossible unless the people were genetically adapted, much as the inhabitants of the High Andes are today, and as the inhabitants of the Tibetan Plateau in the Himalayas and the Ethiopian Highlands are.

And yet this genetic adaptation seems to have occurred within about 2000 years from a founder population for which there is no evidence of prior altitude adaptation, illustrating how a local, highly favourable adaptation, can spread very rapidly through the gene pool, and an 'adaptation' which would have been useless or even harmful in a population with no high altitude to exploit. What was that about all mutations being harmful, creationists?

Incidentally, and something for creationists to consider, birds have no such problem with breathing at high altitude because they have a very much more efficient respiratory system to humans and other mammals. Any thoughts on why an intelligent designer gave us an inefficient respiratory system when it could design such a superior one for birds?

I'll not even bother asking creationists to explain how all South American stuff this fits in with their notion of a special magic creation 6000 years ago because they are unlikely to get past the problem of explaining the dates which are more than 6000 years prior to when they believe everything was made. The cognitive dissonance would most likely be unbearable.

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1 comment :

  1. Interesting as usual, Rosa! Here's another example of rapid evolution, this time among lizards on some islands off the coast of Florida: .

    A quote from that article: When closely related species compete, they may evolve to become different from one another. Called “character displacement,” this process can result in evolutionary changes that reduce further interactions between the species. A. carolinensis and A. sagrei have similar ecologies and occupy similar habitats—they both live on trees and eat insects. So it was no surprise that both were changed by their meeting.


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