From: SJOSEPHS@130.187.170.178 (STEVEN JOSEPHSON)
Subject: Re: Pliestocene extinctions
Organization: Evans & Sutherland Computer Corp.
Date: Mon, 31 Aug 1992 23:31:05 GMT
X-News-Reader: VMS NEWS 1.11


> 
> 
> The Pliestocene North American megafauna went extict around 12,000 years
> ago at the end of the last major glaciation.  This is also the approximate
> date that many believe was when humans first entered North American
> excluding the Bering Strait area.  Several years ago Martin (sorry, I forgot
> his first name) 

Thats Paul Martin

>suggested rather strongly that humans were responsible
> for the extictions of Mammoth, Mastodons, Saber Tooth Tigers, Giant
> Ground Sloths, and the rest of the megafauna, not only in North America, but
> South America as well.  There are elaborate calculations about how fast humans
> would have to migrate to South America to kill off all the animals.
> 
> Larry Agerbaund (I think it was him, and I know I bungled his last name, as
> I'm away from my reference books) wrote that since Martin's article the
> discussion has divided into two camps and almost all articles in the middle
> ground or describing multiple causes have disappeared.  There is another
> whole camp that believes that humans were in North America prior to the
> last glacation, but "hard evidence" is slow to be accepted.  Their estimates
> for the arrival are from 17,000 years ago to 40,000 years ago depending on
> who is doing the arguing.
> 

Paul Martin's argument is based on the fact that when and where humans spread 
in the world, megafauna are quick to disappear. The case can easily be made in
the pacific islands areas (New Zealand and Polynesia especially) that the
arrival of humans (usually with rats) coincides closely with the disappearance
of many large-bodied organisms.  The situation is much less clear as to the
coincidence of the appearance of humans in previously human-free areas like
Australia (~40 K) or the Americas (~12.5 K) and the disappearance of megafauna
at roughly the same time.  There is some evidence that humans and megafauna
coexisted for some interval in Australia, and some that some American megafauna
were dwindling before humans arrived.  The evidence really too thin to support
either conclusion.  One objection to Martin's idea of a "pleistocene
blitzkrieg" is that it is too cut-and-dried: he sees humans waltzing into areas
where the animals have never experienced human predation and so are completely
unprepared to deal with us and too dumb to figure out that we present a danger
until it is too late.  There were, however, substantial ambush predators (which
humans tend to be when it comes to things larger than ourselves) in both the 
Americas (very large cats) and Australia (the marsupial version of a large 
cat), so it is hard to believe that these animals simply couldn't cope.

What seems more likely (and the archaeological record is more clear on) is that
humans did prey on available megafauna when they arrived, but what likely had a
bigger impact on the megafauna themselves is the habitat changes that humans
often envoke, primarily by using fire.  Quite a number of hunter-gatherer
groups on different continents routinely burn land to make it more suitable to
their own purposes.  There is some evidence for this very early on in late
Pleistocene Australia, and such practices could have a dramatic effect on
faunal communities that are harder to imagine occurring by predation alone.

There is an excellent book on extinctions called "Extinctions", and Paul Martin
has a paper in it and may have been an editor as well.  Worth checking out.