Re: Speciation - how do you know?
Gerrit Hanenburg (G.Hanenburg@inter.nl.net)
Wed, 30 Oct 1996 23:33:53 GMT
Paul@crowleyp.demon.co.uk (Paul Crowley) wrote:
>Estimates based on limited data are not "right" or "wrong". They
>have a good or a poor reliability -- and in this case it's poor.
What options do we have? It's much better than estimates based on
nothing. So,until new fossils prove otherwise we may assume that
robusts were not much bigger than graciles.
If you have contrary evidence then please inform us.
>How did early hominids survive nocturnal predation by leopards?
>"Sleeping in trees" is clearly not an answer.
>We have data that needs explaining: two very slow bipeds that
>don't sleep in trees; the first has large teeth with dense enamel
>and apparently consumed a high-protein diet, while the other, with
>the same ancestors and very similar morphology, presumably occupying
>a closely related niche, has very large teeth with extremely dense
>enamel.
Objection. Extreme slowness,not sleeping in the trees and high-protein
diet are assumptions,not data.
Several researchers have reached other conclusions. This we have
discussed at length in the past (remember Stern and Susman? See s.a.p
archives).
>You say (presumably) that the first lived on the savanna, competing
>with chimpanzees and baboons, doing some scavenging and eating
>"something rough" to account for the enamel; that the other lived
>in the same habitat but chose to eat something like small seeds
>(although you can give no reason why that diet needed hyper-thick
>enamel). You say nothing about why they should have speciated;
>nothing about why they became bipedal; nothing about how they
>avoided nocturnal predation; nothing about the reasons for the
>peculiarity of their dental arcade; nothing about their relation-
>ship to later hominids and why they should have changed their diet
>. . . nothing . . . nothing . . .
>
>It's easy to accuse anyone who puts forward a possible explanation
>of "groundless speculation". No one will ever accuse you of that.
>Just keep on saying nothing.
>(This is not personal, BTW -- all professional PA's are the same.)
We know that opinion by now. It's a stereotype.
There are some good professional journals in this field. Did you ever
consult these in order to find out what *is* being said?
>Theoretical. A mouthful of shellfish would have high nutritional
>value.
Have you ever checked the nutritional value of shellfish?
According to my tables the average oyster supplies 208 kJ/100 gm.
edible part. That's comparable to onions (206 kJ).
Check nuts.
>If predation kept Robust population densities low, we would have
>another rough parallel with the chimp/gorilla split. This might
>provide another explanation of respective morphologies. Robusts
>would never be forced to exploit less accessible food resources.
>OTOH population density would soon drive the Graciles to attack
>harder shells, breakable only by stones. Population density would
>also make the intra-species competion fiercer and emphasise the
>use of weapons.
>Consequently, I'd prefer to date the Robust/Gracile split early
>-- before 3.5 mya. Is there any good evidence against this?
If we consider Australopithecus aethiopicus as the first member of a
robust clade (contra Skelton and McHenry) then the First Appearance
Date is ca. 2.6 mya. Your *preference* is ca. 1myr short.
Gerrit
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