Re: Speciation - how do you know?
Gerrit Hanenburg (ghanenbu@inter.nl.net)
Wed, 16 Oct 1996 20:52:23 GMT
Paul@crowleyp.demon.co.uk (Paul Crowley) wrote:
>In general, we should be able to assume that both late and early
>hominids exploited shellfish. We have extensive evidence throughout
>the world of H.s.s. exploitation for the last 100 kya or so.
>It requires no technology that was not available to early hominids
>or, indeed, is beyond the capacity of chimps, or even otters.
>They just have to be able to use stones to break open shells.
>If they were doing it 100kya, why not 5 mya?
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.
Until something like that is discovered I suggest we accept as a null
hypothesis that australopithecines didn't use marine resources.
>Is such an activity too boring, too unadventurous, too unimaginative
>for us to allow that it might have been the main activity of *all*
>our ancestors?
Given their primate affinities and the fossil record I don't think
it's likely.
>A remarkable feature of all hominid dentition - from 4 mya to the
>present - is the depth of the enamel layer. It has no explanation.
>IMHO it probably resulted from having to cope with shell chippings
>in the diet.
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 hominoids are characterized by relatively fast growing pattern 3
enamel prism packing,but in the African apes it is followed sooner by
a fase of slow growing pattern 1,which eventually results in thinner
total enamel. In fact the enamel prism pattern together with the
knucklewalking complex is a strong indicator of an African ape clade)
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.
Gerrit.
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