Re: Refs, please... was... Re: AAT Theory
H. M. Hubey (hubey@pegasus.montclair.edu)
21 Oct 1995 19:15:38 -0400
David Froehlich <eohippus@curly.cc.utexas.edu> writes:
>> was from forest-dwelling to savannah/steppe/grasslands-dwelling.
>Funny thing, we have evidence from the fossil record that this change
>actually occured. Why is it so difficult to accept? I think you
>misunderstood slightly, in that I make no assumptions about the total
>environment during the middle to late Miocene and so I
No, you misunderstood. It's the environment that produced the
bipedalor I was talking about not the change all over the earth.
And no, there's no difficulty accepting the large scale environmental
change.
>environment we can study, the morphology of the proto hominids would
>indicate a forest habitat). Paleoclimatologists and paleobotanists tell
Its grasping big toe would not have disappeared as soon as
they stopped climbing. And if they kept climbing it would
have offered an advantage. So there's a time lag between
morphology and behavior.
>us that between 10 and 5 mya in Africa the environment changed to warmer
>dryer conditions. Similar evolutionary changes occured in elephants (we
I must admit I can't comprehend this without more info. It it
got warmer then more ice melted, oceans rose. More water to
evaporate and to fall back down on the earth.
Cause and effect seems to be skewed. I'd guess that trees were
pulling moisture out of the deep ground and evaporating it
into the air which fell back down as rain and nourished shallow
root plants. Maybe the forests started to disappear due to some
other external cause which caused a drop in atmospheric vapor
and hence rainfall leading to drying. That means to me
that plant eaters wore out the habitat. But then this change
above would have starved them or by that time predators would
have been having a field day, every day. So now we seem to have
a cycle of poverty of prey starting up. Under these circumstances
the predators should have been going after everything in sight.
BTW, what caused the changes to dry and warm climate?
>went from anuncine gomphotheres to true elephants in this period of time)
>and many other organisms. Is it not parsimonious to hypothesize that
>proto-hominids reacted to simialr changes and evolved?
No, but again, in order for them to get large would have been
difficult without a cooling off mechanism. Water provides it,
along with explanation of their size and their nakedness.
>No movement is required if the environment is changing around you. It is
>either adapt or die.
OK. If the forests all disappeared and grasses burned out then there'd
be wholesale loss of planteaters and predators that fed off them.
Then they'd need something really special to be able to survive
this kind of a catastrophe.
>But AAS does presume that they spent enough of their time in the water to
>adapt to it. This is the basic premise of AAS. Do not change the target.
I didn't change anything. I still don't see any reason not to
believe it.
>Forest to mixd habitats, hominids probably did not occupy pure grasslands
>until at least Homo erectus.
We're into fuzzy variables again. Check out the CEHE and tell me on
that scale what your idea of "forest" and "mixed habitat" is so
that I have a better idea. It goes from something like triple-canopy
forest to grasslands. When I go home I'll post the page number and
the scaling on the page in case it's inconvenient to find the book.
>You make the unwaranted assumption that all of the forest had to be
>changing into grasslands. For gorillas and chimps to evolve all we need
>is some of the forest to remain forest. If the last common ancestor was
No, I don't. In fact, the opposite. If the bipedaling wimps were
running from forest to forest (or wood patch to wood patch) then
they were still arboreal and I don't see much reason to think that
they'd become bipedal. If they lived in the forest, then there's no
reason to change at all. They had to have a serious change of
life style, and a selection mechanism that produced it. There's no
advantage at that time of running bidally; it would be too slow.
So far all we got is things like; they get less sun on their
backs if they stand up.
>equally explanatory. Finally, I agree it is not a binary problem, there
>is AAS on one hand (and possibly some variation) and a multitude of
>different explanations in the terrestrial realm (you could probably get
>any ten different paleoanthropologist to give you ten different scenarios)
>> 3) Elephants and hippos are allegedly naked because they are large.
>> This could be putting things backwards. Marine animals are the
...
>You left some things out, what about sauropods while your at it.
>(sauropods were completley terrestrial and hairless)
I don't know anything about sauropods. If they belonged to the
dino family I don't see how you'd know they were hairless except
via indirect guessing. And there could be other reasons. i don't
know anything about the environment at that time either.
>In your above statement I challange you to demonstrate causality. Is
>hairlessness because they are big, big because hairless, big because they
>are using water, using water because they are big, hairless because they
>are using water, using water because they are hairless? Which one?
You need a process (dynamical) view not a state (static) view.
Start from small, and then see how they get large. They can't
just get large without the overheating bit. It's possible that
they can get large and also have the adjustments needed as they
get large, i.e lose hair, get big ears (increase surface area)
etc. But without knowing more about evolution, I can't see why
every animal can't go this route. Being big has advantages; you
can knock around smaller animals and don't have to fear predators.
But this works for every animal. So something else has to be
hapenning. I gave an explanation of what makes sense to me
within the narrow scope of this discussion.
It's probably much more complicated. I don't have time now for it.
--
Regards, Mark
http://www.smns.montclair.edu/~hubey
|