Re: An alternative to ST and AAT
Gerrit Hanenburg (G.Hanenburg@inter.nl.net)
Wed, 13 Nov 1996 17:14:16 GMT
Paul@crowleyp.demon.co.uk (Paul Crowley) wrote:
>Thanks for all the detailed information, and apologies for my
>(near-)duplicate postings. My internet provider is having major
>difficulties and I thought the first had got lost in cyberspace.
That's what I thought of mine too.
>2.5 Myr comes from speciation at about 5 Myr and the origin of
>the homo line at about 2.5 mya. It is probably too long.
At the moment the earliest reliable indication of bipedalism is the
KNM-KP 29285 partial tibia,assigned to Australopithecus anamensis (FAD
is 4.2 Myr).
>Lucy *could* have climbed other kinds of trees, but did she?
>There must have been some change in habitat. Surely it has to
>be a separation from the kinds of trees in which her pre-hominid
>ancestors slept? A translocation to a equatorial rain-forest
>could help to justify the new morphology.
But the rainforest was exactly the kind of biome that was disappearing
in late Miocene/early Pliocene eastern Africa. In its place came a
diverse mosaic of forested and more open country with increased
Why would an ape change its anatomy in the direction of Lucy's design
when staying in its original habitat? In the rainforest there was no
need for bipedalism and it already had the design of a skilled
Lucy's climbing abilities don't need a new explanation because it's
what she inherited from her ape ancestors. Only what's new needs an
>> >So why was a shorter leg maintained for 2.5 Myr?
>> Because long legs get in the way when climbing trees . . .
>Is this true? I can see it when trying to climb vertical pole-
>like tree trunks, but not otherwise.
Getting in the way was not meant litterally.
It depends on the form of climbing;hindlimb dominated (e.g.lemurs and
galagos) or forelimb dominated (apes). In the latter case shortness of
the hindlimbs is favorable in relation to the forces that act on the
knees and hips (see Preuschoft,H.and Witte,H.(1991),"Biomechanical
reasons for the evolution of hominid body shape" in Coppens,Y. and
Senut,B.,"Origine(s) de la Bipedie chez les Hominides",CNRS
>Efficient long distance travel is always desirable. Something
>which prevents it must be important.
Efficient long distance travel is only desirable if you have to travel
long distances. That is,natural selection will only opt for it in an
environment were it pays and in so far as it is compatible with other
requirements. Emperor penguins sometimes have to cross many miles of
ice before reaching open water,yet their form of bipedalism is not
very efficient because they also have to be good swimmers.
A.afarensis was undoubtedly more efficient bipedally than a chimp,but
probably less than H.erectus. The reason was that A.afarensis didn't
have to be as efficient as H.erectus because it didn't have to cover
the same long distances and because its bipedality had to be
compatible with a certain degree of arboreality. Like chimps
A.afarensis had a compromise anatomy.
>With a high shellfish diet, you'd also need lots of fresh water to
>eliminate the salt. They go together.
Which means the littoral ape needed a more or less continues access to
fresh water.Could be a problem in a littoral environment.
>> You can't life for extended periods on a diet with a protein
>> content that exceeds 50% of total calories. Even Alaskan
>> Eskimos,who have the highest protein intake,have a diet in which
>> protein contributes only 22-25% of total calories.
>You are talking about H.s.s. All predators can take much more.
>There is no reason why the Australopithecines could not have
>adapted to a diet with a somewhat higher protein content.
>(What else did traditional Eskimos eat, btw, especially in the
We are talking about primates here who's digestive system and
metabolism are mainly adapted to frugivory/folivory.
Full-time predators with a long evolutionary history of predation are
hardly adequate comparative material.
Contrary to shellfish the meat of artic verbrates has a high fat
content which results in a high caloric value. Eskimos do not have to
rely on protein for their energy and can subsist on animal matter
alone during winter. Protein content does not exceed 30% of total
>We're looking at about 2 Myr for the australopithenes. During all
>this time they have to be at least as efficient in gathering these
>resources as their competitors: baboons, monkeys, chimps. They
>have to be at least as effective in avoiding nocturnal and diurnal
>predators. They have to have some particular "edge" or advantage.
>It can't be better speed at getting around.
Apparently I have a somewhat different view on community ecology than
you. If I look at todays wildlife communities in Africa I see numerous
sympatric species of bovids,large carnivores,monkeys,birds,etc. I
wonder how they all manage to have a particular "edge" over the
others. What "edge" do you think Vervet monkeys have over Savanna
baboons,Ruppell's Griffon vulture over White-backed vulture,and
Grant's gazelle over Thomson's gazelle?
Could it be that community ecology and the evolutionary dynamics of
biological diversity is a little more complex than just interspecific
>Well, I have a hypothesis. What's your's?
What have we been discussing lately?
I have several ideas on different aspects of hominid evolution which I
have been discussing in this newsgroup for about two years now.
I simply do not favor one monolithic hypothesis.
Gerrit (who thinks monotony is the death of fruitful science)