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Re: Pleistocene/Holocene extinctions



This discussion always suffers from the fact that there is no clear and 
consensus criteria for determining the cause of extinction; e.g., if a very 
large population of animals is reduced by longterm drought to a very few 
breeders, and those remnants are then eaten by hunting humans, what is the 
cause of extinction? If you say "humans", then humans were huge as a "cause" of 
Late Pleistocene extinctions. Otherwise, you must give a nod to the factors 
that reduced these populations to the point where they were vulnerable.

Personally, I think there is a lot stuff in the record that would have made 
through the various climate changes, if "primitive" hunters hadn't appeared on 
the stage, but those populations were viable enough to have withstood early 
hunting pressures if unstressed by climate change. Then again, any animal large 
enough and slow enough to be profitable to kill was probably doomed in the long 
run, anyway. So I say, "humans". And we may just be getting started ...

Don

----- Original Message ----
From: K and T Dykes <ktdykes@arcor.de>
To: trex_kid@hotmail.com
Cc: dinosaur@usc.edu
Sent: Thursday, September 20, 2007 7:22:29 AM
Subject: Re: Pleistocene/Holocene extinctions

A counter objection to climate change having fired the gun would be that
similar changes occurred before, and left no obvious signs of extinction.
Mammoth steppe, for example, had expanded and shrunk, expanded and shrunk
merrily and, regardless of the fluctuation, somewhere or other some mammoths
were still able to make a living and enjoy sexual relations (obviously only
within marriages involving one mammoth of each sex -this was before the
nastiness caused by apple-eating).

In some cases, it's hard to believe it wasn't funny primates with sticks
(and hard stones) what did it.  The case appears overwhelming for Madagascar
and New Zealand.  At least, it does from my not particularly well-informed
viewpoint.  Then again, those are geographically isolated places making
escape by migration elsewhere tricky.  The same often doesn't apply for dirt
big continents.

One possibility would be to combine both elements.  Mammoth numbers dwindled
due to a loss of mammoth steppe, and hungry humans -who had a history of
using some indiscriminate methods of mass slaughter, such as driving herds
of the things over convenient cliffs- carried on with their traditional
techniques.  As this was in combination with a much smaller target
population, the human normality could've been abnormally destructive.  I
voice this only as a possibility, not as anything as grand as a sketchy
hypothesis.


----- Original Message -----
From: "Brandon Pilcher" <trex_kid@hotmail.com>
To: <dinosaur@usc.edu>
Sent: Thursday, September 20, 2007 12:56 PM
Subject: Pleistocene/Holocene extinctions


>
> Sorry that this is not related to dinosaurs, but it does concern
paleontology, so here goes...
>
> What is the most widely accepted and/or likely theory for the mass
extinctions in Eurasia, the Americas, and Australia at the
Pleistocene/Holocene boundary? Many people attribute them to human
overhunting, but my beef with this conjecture is that Africa does not seem
to have been affected nearly as badly, even though African animals should
have been the first to go according to this model.
>
> My opinion is that climate change was the most important factor. The
failure of many species to adapt to quickly changing climate patterns seems
more likely to cause so many extinctions than a few primates with sharpened
sticks.
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