Re: New Savanna Man from China 2 mya

"Paul Crowley" <slkwuoiutiuytciuyik@xxxxxxxxxxxxxxxxx> wrote:

Recent Homo sapiens is not an appropriate model for hominoids under
natural circumstances

True -- but it should be assumed that the
modern species occupies much the same
habitat as its ancestors. We cannot think
clearly about the ancient presence and its
extent without first trying to remove from
the scenario the modern presence,

Hint: correlation between body size and home range area.

The absence of large predators from
islands (such as Borneo) is the result of
an inability to maintain a viable population.
Whereas hominoids, such as orangs, which
eat a wide range of mainly vegetable matter,
can and do survive in such places.

But then Borneo is huge (over 700,000 km^2), has a very high primary
productivity throughout the year, and is not predator free (Neofelis).
There is nothing like it near the African continent except for
Madagascar, which has been separated from the African continent for
tens of millions of years.

Borneo is one example -- of what happens
to populations, especially of predators,
when they become isolated on islands.
As sea-levels have risen and fallen over
the past 6 million years or so, many islands
of various sizes would have been created
and eliminated.

But nothing on the continental shelf of Africa that would be much
larger than Zanzibar. That may be just about enough for a tiny
cercopithecoid but not for a large-bodied hominoid.
Or else, where?

With an area of approximately 1600 km^2 and a population of over 1
million the population density of Zanzibar is more than 600/km^2. That
is way above the carrying capacity of the natural environment and can
only be maintained through a modern technological economy based on
imports.
The proper model in this case would be one of the great apes, in
particular Pan. Kano ("The Last Ape: Pygmy Chimpanzee Behavior and
Ecology", Stanford Univ. Press, 1992) reports population densities of
1.7 /km^2 for Bonobo at the study sites and as low as 0.4/km^2 for the
whole region.

Gombe yields a figure of about 1 km^2 per
adult chimp -- but that is also with a dense
population of baboons.

Does confirm the earlier figure. And you also have to assume that
every square kilometer of the island would have enough productivity to
support hominoids. Presence of subprime and marginal habitat would
further reduce the carrying capacity.

Convert that to the area of Zanzibar and you get a total
population of less than 1000. That's very small from a population
genetics point of view and very susceptable to collaps and extinction.

A small population would have been right for
the initial speciation and the development of
bipedalism.

And suffer major inbreeding since the breeding population would be
even smaller than the total population.

The evolution of larger groups
would have enabled the elimination of baboons,
allowing a much higher density.

Which is based on the unfounded assumption that the protohominid would
have a competitive advantage over baboons. The cohabitation of baboons
and chimps elsewhere clearly is an argument against it.

And it certainly would not be enough as a source for mainland
immigration.

Every viable population of every species
will necessarily produce a surplus.

Yeah, many more individuals are produced than could possibly survive
on the available resource base. That's an old one.
And then most of the surplus is eliminated through environmental
constraints (and that includes other competing species). And as long
as our protohominid is on the island it has nowhere else to go.
And when the island finally makes contact with the mainland the few
individuals that make it every generation would find themselves in a
competitive world of mainland experts where they do not fit. Or even
worse but more likely, the mainland fauna, with much larger source
populations, would swamp the island and drive the "dodo's" to
extinction.

It might not have been as hard as we
usually imagine to avoid predation --
IF the hominids were able to discourage
the predators from seeing them as prey.
Of course, that would require a low
level of contact between the species/

Basically that means staying off the mainland, because most predators
there have no problem with identifying primates as prey, even as
bipeds.

The difference between me and you
(where 'you' includes all standard PA
types) is that I am seeking for a solution
to the problem of predation. You (i.e. 'you-
all') rarely acknowledge it -- but when you
do, you insist that it was insuperable.
(Some contradiction somewhere?)

I certainly acknowledge the problem. The co-existence of early
hominids with predators in the fossil record is a given. And evidence
for predation is very suggestive, witness the puncture holes in SK 54,
matching the size and spacing of the canines of leopard specimen SK
349. http://web.inter.nl.net/users/G.Hanenburg/Swartkrans.jpg
With Homo I don't see much of a problem. A more culturally advanced
and large-bodied taxon like Homo erectus would have been capable of
protecting itself against predation. About the apith grade of hominids
I'm more worried. A critter like Lucy, particularly in the open, would
have been no match for a lion.

Basically that means staying off the mainland, because most predators
there have no problem with identifying primates as prey, even as
bipeds.

Predators which see their prey species
regularly -- e.g. every day or every week
-- will know what they are, especially if
they see the more vulnerable members
and are able to catch them on occasion.
I believe that hominids could keep their
females and infants safe at a home base
-- preferably an off-shore island, but a
peninsula might have worked -- while the
males patrolled the hinterland in fairly
large groups, locating and killing cubs or
pups and getting the adults to move away.
In this manner, the predator species would
not have contact with hominids on the
usual predator-prey basis. They would
have come to regard hominids as an
unpleasant source of trouble, to be
avoided -- which is still their attitude.

Of course, the great bulk of individuals
in the predator species would never come
into contact with hominids. On encountering
one or more hominids they would not have
seen them as prey.

I find that an highly unlikely scenario as per my comment above.

Third, there is a rich fossil record of inland continental hominids
going back some 7 myrs that simply cannot be explained as a collection
of strays continuously emanating from an island source.

Why not?

Without it (or a better idea) you are obliged to
contrive scenarios where two or more species of
hominid co-habited in the dry upland deserts of
Africa, finding quite distinct niches.
http://news.bbc.co.uk/2/hi/science/nature/6937476.stm

Well. first of all we're not talking about upland desert here.

Your refer above to the "rich fossil
record of inland continental hominids"
After 2.4 mya that was a very dry place.

But it certainly was not a desert.
It was seasonal, but average annual precipitation would still be large
enough for high primary productivity (witness the enormous biomass),
and provide water and food to last through the dry seasons, although
that meant increasing reliance on lower quality fallback foods at the
end of it.
You need to catch up with your savanna ecology.

Next to
rainforest African savanna (sensu lato) is one of the terrestrial
biomes with the highest primary productivity, be it on a more seasonal
basis.

That's beyond irrelevant -- it's absurd.
Hominids have no adaptations for
consuming its resources -- grass and
the animals that eat grass.

There's more to the savanna biome than that.
And the hypermasticatory morphology of Paranthropus would certainly be
able to process many of its plant resources. Homo on the other hand
would need to develop a more technical approach, which it did.

Second, in such habitat sympatry of closely related species
with overlapping niches is not unusual (there are many examples from
felids, canids, primates, and ungulates).

Hominids are supposed to be adaptable.
This is the mantra we get all the time from
standard PA: hominids could live anywhere
and do anything. These supposedly over-
lapping co-habiting hominid species were
relatively late. The notion that they would
specialise to the extent that neither would
significantly 'poach' on each other's resources
is quite absurd.

Well, eventually Homo may have contributed to the demise of the
australopithecine grade, but Paranthropus and Homo were
morphologically different enough to occupy different niches in the
same environment. Put these two next to each other and your looking
two very different grades of adaptation:
http://web.inter.nl.net/users/G.Hanenburg/Paranthropus_Homo.jpg
The differentiation here is bigger than between lion and leopard.

And it gets even further
beyond rationality to claim that they would
do it in a desert.

What desert?

Gerrit
.

Relevant Pages

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