drpaleo said:
Andre raises a few interesting and informed points, but he is profoundly wrong, I think in his dismissal of Martin's hypothesis. I will explain at length later. Watch for my article forthcoming next December in Gary Haynes' edited volume (Springer Press).
Looking forward to a discusion in due time. Meanwhile, this would be my introduction to the discussion.
the overkill hypothesis is described very well here:
http://www.amnh.org/science/biodiversity/extinction/Day1/overkill/Bit1.html
http://www.amnh.org/science/biodiversity/extinction/Day1/overkill/Bit2.html
http://www.amnh.org/science/biodiversity/extinction/Day1/overkill/Bit2.html
The essence:
According to the overkill hypothesis, when ancestors of native Americans entered North America about 14,000 calendar years ago, they encountered a large number of species that had no experience with humans. As a result, they did not recognize humans as a threat. The ancestral Indians (or Paleo-Indians, as they are sometimes called) were able to take advantage of this fact and were able to hunt the large mammals with great ease. The Paleo-Indians became specialist big game hunters concentrating on game like mammoths, giant bison, ground sloths, and other species of large size. They hunted dozens of species to the point of extinction, and indirectly caused the extinction of many smaller species as a consequence of ecological disruption.
Because the evidence is mounting that the North American extinctions occurred very rapidly--perhaps in less than 1,000 years--Martin has dubbed the hypothesized overkill event as a "Blitzkrieg" or "lightning war."
We would focus on the question if the overkill hypothesis can be falsified.
The first element is the entrance of humans (Clovis) in N America at 14,000 calendar years ago (assumingly via the dry Beringia landbridge), not before. The main debate has been about the before-Clovis dating of artefacts or if the artifacts were genuine, however I will demonstrate that other evidence, following from abundant research of
mitochondrial DNA and human parasite migration raises some doubt about this earliest migration. Obviously, an earlier entry would falsify the blitzkrieg idea.
A second element is the synchronisation. It appears that some species were in the full process of dying out, as determined by declining sizes of fossil bones (horses) before the human arrival; while others survived the assumed first strike for some millenia (mastodon)
A third element is the environment, climate and biotope changes. During all of this there should not be any climate changes that could have lead to extinctions, neither in the Americas nor elsewhere. I will demonstrate that massive extinction events in South America and Eurasia cannot be linked to anthropogenic causes, while there was lot's of simultaneous climate changes going on, changing the biotopes, including in North America. This in turn favored other species, better equipped (modern bison), competing with the doomed species and taking over the changing niches.
A fourth element is the apparently missing earlier megafauna extinctions during equally violent climate changes during the Pleistocene (2.5 Million years - 10,000 14C years ago). However, absence of evidence is not evidence of absence. And the earlier paleonthologic remains are much much more scarce. Nevertheless, it shows that the species overturn rate during the Pleistocene was substantial, many species did go extinct indeed to be replaced by other. However these mineralized remains cannot be dated accurately since the original material was replaced. So it's not possible to esthablish an adequate chronology for these remains and establish a pattern for extinctions. Moreover, the main killer, the transitions in and out the Younger Dryas, appears to be unique indeed during the Pleistocene.
In conclusion, while it would not be disputed that migrating man might have killed off many naive specimens, nevertheless all the elements were there for the climate to do the real job, which may perhaps have included eradicating Clovis himself as well, as it seemed to have vanished completely with his alleged victims.
So where would that thread go? Biology or Earth?
References here (excluding the anthropologic publications, those will follow later)
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