Re: Absolutely Bonkers

Noone Inparticular wrote:

> John Harshman wrote:
>
>>Glenn wrote:
>>
>>>"John Harshman" <jharshman.diespamdie@xxxxxxxxxxx> wrote in message
>>>news:tM%Ne.1$A%1.0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>>
>>>
>>>>Glenn wrote:
>>>>
>>>>
>>>>
>>>>>http://news.bbc.co.uk/1/hi/sci/tech/4160560.stm
>>>>>
>>>>>"If a group of US researchers have their way, lions, cheetahs, elephants and
>>>>>camels could soon roam parts of North America, Nature magazine reports. "
>>>>>
>>>>>[...]
>>>>>
>>>>>"But man's arrival on the continent - about 13,000 years ago, according to one
>>>>>prevalent theory - pushed many of these impressive creatures to extinction."
>>>>>
>>>>>And hasn't, where man supposedly originated and lived for much longer.
>>>>
>>>>This is the non-bonkers part of the story. What do you mean by
>>>>"supposedly" here? Do you think that man didn't originate in Africa, or
>>>>live much longer there than in America? If so, why?
>>>>
>>>>As for the lack of overkill in Africa, the theoretical reason is that
>>>>the biota there evolved along with humans, and thus adjusted to them.
>>>>
>>>
>>>So the theory that many of the animals were pushed to extinction is "non-bonkers",
>>>and the "theoretical" reason that the same didn't happen in Africa is that the
>>>animals "adjusted" to humans. In a later post you seem to suggest that at least
>>>one reason that the animals in the America's were pushed to extinction is because
>>>they were not adapted, or "adjusted" to humans, and I assume you cite as evidence
>>>an example of an animal that has not adapted to humans, the dodo bird.
>>>This is great stuff, John.
>>
>>Thanks.
>>
>>
>>>>From the article:
>>>"During the Pleistocene era - between 1.8 million to about 10,000 years ago -
>>>North America was home to a myriad of mega fauna. Once, American cheetah (Acinonyx
>>>trumani) prowled the plains hunting pronghorn (Antilocapra americana) - an
>>>antelope-like animal found throughout the deserts of the American Southwest - and
>>>Camelops, an extinct camelid, browsed on arid land. But man's arrival on the
>>>continent - about 13,000 years ago, according to one prevalent theory - pushed
>>>many of these impressive creatures to extinction."
>>>
>>>I don't see an animal that has virtually no predators here, nor the dodo. And it
>>>appears that if your "theory" is correct, that the extant animals of the America's
>>>would have "adjusted" to humans within 13,000 years.
>>
>>Where do you get this? Because the ones we have left now have adjusted?
>>Perhaps they were the ones least vulnerable to extinction already, for
>>whatever reason. The majority of extinctions were the largest animals,
>>the ones that had the smallest populations and offered the largest
>>amount of protein per kill. And this extinction happened over a short
>>period, much shorter than 13,000 years. For all we know all large
>>animals became extinct within a few tens of years after human arrival in
>>an area.
>>
>>In Africa, in contrast, large animals would have had millions of years
>>to evolve defenses against human predation, as human technology
>>gradually increased. By the time humans had efficient weapons like bows,
>>they may have become wary enough to make approaching them difficult and
>>time-consuming.
>>
>>This theory may not be true but it's hardly "bonkers".
>>
>>
>>>I find that amazing, and
>>>perplexing at the same time. The few animals that were lucky to possess traits
>>>which somehow led them to run from or succesfully hide or defend themselves from
>>>humans passed these traits on and eventually became fixed in the population in a
>>>blindingly short period of time. The pronghorn would have had no defense against
>>>humans, since they had no fear, I suppose is your concept.
>>
>>Perhaps, though it may be that having a large predator already made them
>>skittish of any unknown, large animals. Many of the extinct species
>>would have had few or no predators -- at least on adults -- until humans
>>arrived.
>>
>>
>>>But how do we explain
>>>deer and pronghorn, probably slower 12,000 years later, not being driven to
>>>extinction? Did red man become one with mother nature and brother bear?
>>
>>Slower? Certainly humans could have hunted deer to extinction if they
>>had worked hard at it. But there are feedbacks here. Hunting reduces
>>populations, making hunting less rewarding. I see no reason why an
>>equilibrium couldn't be reached. The problem with large animals is that
>>their populations were small and, when they became rare, they could
>>still be encountered when hunting smaller animals whose populations had
>>not crashed.
>>
>>There are all manner of uncertainties here. My point is that you can't
>>just say the hypothesis is silly on the basis of some imagined
>>impossibility.
>
>
> It seems likely that humans acting alone could not be the cause of
> most, if not all, of the extinction of the Nth American megafauna
> refered to here. Despite some of the claims I've seen here, humans are
> not really very good hunters. Certainly during the time of the
> mega-fauna extinctions there were very humans on the continent. It is
> population size, not hunting ability that has resulted in human caused
> extinction.

Not quite true. Some species have indeed been hunted to extinction. It's
especially easy to do with megafauna that have small populations and
long generations. At any rate, the pattern is not just in North America.
It's also in South America, Europe, Australia, and vast numbers of islands.

> ISTM, that some Nth American megafauna, such as the mastodons and giant
> bison probably died off because of a combination of human predation and
> severe loss of habitat. Humans arrived (perhaps not coincidentally) as
> the great glacial sheets were retreating. The kind of sub-glacial
> environment that some of these animals may have been adapted for, thus,
> was disappearing just as a new predator arrived. The animals were
> doubly hit; a new environment and a new predator, both of which they
> were not ready for. Which pressure was most important? My feeling is
> that to the extent that humans had any impact at all, they just finshed
> off (or accelerated) a process that was already underway.

That would imply a worldwide, simultaneous extinction. But this isn't
what happened. The various extinctions on different continents and
islands happened at different times, coinciding quite nicely with the
dates of human settlement.

.

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