Re: Speciation - how do you know?
Paul Crowley (Paul@crowleyp.demon.co.uk)
Thu, 17 Oct 96 09:13:01 GMT
In article <543i23$gm0@news.utrecht.NL.net>
ghanenbu@inter.nl.net "Gerrit Hanenburg" writes:
> Paul@crowleyp.demon.co.uk (Paul Crowley) wrote:
>
> >In general, we should be able to assume that both late and early
> >hominids exploited shellfish.
>
> It's not that they *couldn't* have done it but we simply have no
> indication *that* they did it. There is no australopithecine
> equivalent of Grotta dei Moscerini.
Nor is there likely to be. Neanderthals and H. erectus probably
had fire, animal-skin clothing and blankets and the ability to
build shelters. They could travel to remote coastal sites, a very
small number of which have subsequently been geologically raised.
Australopithecines, with a lifestyle significantly dependent on
shellfish, had no such ability. They would have been restricted
to coastal locations in a warm non-tidal sea.
> Until something like that is discovered I suggest we accept as a null
> hypothesis that australopithecines didn't use marine resources.
You can set impossible standards of proof for any hypothesis.
When direct evidence is unattainable, you have to look at more
circumstantial matters. It's often a choice between various
theories, none of which have direct evidence. It's sometimes
a choice between a theory which explains the data and no theory
at all.
> You suggest that thick enamel in early hominids is a derived character
> that evolved in response to an abrasive diet.
> But it is quite possible that thin enamel (as in Pan and Gorilla) is
> the derived condition and that thick enamel characterizes the LCA of
> humans and African apes,since fossil hominoids such as Sivapithecus
> also have thick enamel. Thus it may be a primitive retention.
All hominids (including H.s.s.) have thick enamel. It is absurd
to say that H.s.s. enamel is a primitive retention from an LCA
7 mya - which is implied by your argument. Enamel (and dentition
generally) is expensive and will evolve rapidly in new circumstances.
(H.s.s. dentition has decreased in size by 20% in the last 20kya,
presumably as a result of consuming soft cooked foods.) Thick enamel
could come and go in less than 100kya under strong dietary forces.
> I don't deny that thick enamel in the earliest hominids *was* an
> adaptation but it may have been present already in the LCA and
> probably had nothing to do with shellfish.
The exceptionally thick enamel of the earliest hominids needs
an explanation; so also does the thick enamel of all hominids,
including H.s.s. How many explanations are there?
Paul.
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