Re: Speciation - how do you know?

Gerrit Hanenburg (
Fri, 18 Oct 1996 22:21:41 GMT (Paul Crowley) wrote:

>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.

Explaining the data is not enough.
I'm sure the littoral ape theory has an explanation for the
differences in tooth structure and facial architecture between
A.afarensis and A.boisei that undoubtedly involves shellfish. Ad hoc
explanations without testing will get you anywhere.

>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.

How do you determine whether or not a certain tissue is expensive?
I would say that brain tissue is metabolically expensive since it
requires a relatively large supply of oxygen(3.5 ml/100gr./minute),but
how is that in case of teeth?

>(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.

That would only indicate that enamel,like bone,is very plastic in
response to selection pressure. It says nothing about being expensive.
I suppose cartilage too is responsive to selection pressures despite
the fact that it is one of the least metabolically active tissues.

>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?

Thick enamel may very well be a response to an abrasive diet,but a
diet can be abrasive in different ways. Crushing shellfish is only one
of them. (and unlikely in the case of primates)
Why do Orangutans have thick enamel?