Re: Bipedalism in different substrates

From: Jason Eshleman (jae_at_vidi.ucdavis.edu)
Date: 07/15/04 

Date: Thu, 15 Jul 2004 17:49:23 +0000 (UTC)

NA Sides <nas@sonic.net> wrote:
>On 14 Jul 2004 01:44:57 -0700, algis@RiverApes.com (Algis Kuliukas)
>wrote:

>>Wetlands are food rich. Use your imagination.
>
>Sorry, I can't imagine any combination of wetland resources that would
>support populations of hominins. Apparently you can't either. You've
>had years to do so and all you've come up with are unsubstantiated and
>implausible claims about crab-grabbing and one crab supplying an
>entire day's food.

This is an important issue. I'm not sure if a particular wetland could or
could not support a population of hominids without sophisticated tools.
It depends, of course on the wetlands. I know that in my part of the
world, native populations lived near marshlands and did acquire a
significant amount of their resources from wetlands, though they were
generalists, also utilizing a signficant amount of "dry" resources. I
don't doubt that there are some wetlands that can support some ape
communities in terms of total calories available.

But the availability and ability to get at these calories are different
things. Where we see modern hunter-gatherers subsisting in wetlands,
they're doing so with sophisticated tool-kits and big, creative brains
that the earliest bipeds (and presumably their pre-bipedal ancestors) did
not have. Foraging isn't simply a matter of stuff being there, it's about
the return on investment in trying to get at the resource.

It's not at all implausible that there were resources in the water that
some apes could have gone for. But again, how much is important. If it's
just part of the diet of a generalized forager, it doesn't seem likely
that specialized wading traits would have evolved. I say this because, as
NAS points out, they haven't evolved in other generalized foragers who
utilize aquatic resources. There *isn't* some property of selection
whereby *any* exposure creates a need for optimalization to the
environment of limited exposure. Insistence that *any* wading selects for
better wading is an abuse of the science. It's especially problematic if
the changes necessary for "better" wading compromise locomotion in
environments that they spent far more time in. This of course leads to
one of the apparent mysteries of bipedalism. It's slower than most forms
of quadrupedalism, even knucklewalking. If changes resulting from wading
for a few minutes cost you for the other 23 hours, 55 minutes, the
advantage isn't going to be selected. Again, this is why it looks like
the wader needs to be an aquatic specialist, or at the very least heavily
reliant on resources it can only get by getting its feet wet, in order for
some wade-for-dedicated-bipedalism selection to be going on.

The need to define the diet, or at least come up with reasonable guesses
to test is important because we don't have direct evidence of the time a
"more aquatic" ape would have spend in the water. It's not at all
sufficient to use your imagination and posit that crabs or sedges or
whatnot could have sustained these creatures, or even contributed greatly
to their diets such that there would be specializations just to get these
morsels.

[Somewhat related--M. fasicularis, the "crab-eating" macaque, does hunt
crabs from time to time, though it's a generalist and lives quite well out
of mangroves swamps where there are no crabs. When it does grab crabs,
they aren't the big oceanic crabs where one could support even a macaque
for a day, but smaller crabs that typically inhabit mangrove swamps.
They're a largely arboreal species that tends to come to the ground only
when they're right at the water's edge. Sufficient to say though, there's
no evidence that they've got any bipedal adaptations for getting the crabs
on any of the other marine stuff they eat. Despite the name, 90% of their
diet is fruit.]

Diet breadth changes with technology as resources become easier to
acquire, so modern peoples are not always a good indicator of what's
available to a non-technological hominid. Far ahead of proposing that
wading could have presented the selective environment that favored a
change to obligate bipedalism (a selective regimine that I don't thinki
has been addresse3d beyond assertion) is justifying that wading likely
happened with a regularity that would make some specializations favorable.
Again, bears, even bears who spend hours a day wading out for fish, do no
appear to have any "wading efficiency" adaptations, nor do raccoons.
Since Algis's argument for longer legs seems to be that getting in
progressively deeper water is progressively better to some degree, the
actual resources are important. Do other waders really do that much
better by going into deeper and deeper water, or do they stay in shallows
because that's where the stuff they can get easily (and by easily I mean
at a point where the cost to acquire is less than the benefit of having).
Just because stuff is there doesn't mean it makes sense to get it.

Defining a diet is *more* important for a wading model than a terrestrial
model because we know that there are terrestrial environments that can
support apes because terrestrial environments *do* support apes. If the
wading doesn't open up enough positive return foodstuffs, then the "rich"
environment is moot. If it does, it's a reason to consider how much
wading might be reasonably expected to have occured. At that point it's
reasonable to start figuring out plausible time budgets.

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  • Re: Bipedalism in different substrates
    ... >>the wading behaviour a very marginal one. ... While apes may live in "wetlands" (quotes because this too is ... that "aquatic" resources seem at most to ... further exploitation results in reducing returns on investment. ...
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