Re: Speciation - how do you know?

Gerrit Hanenburg (
Sat, 26 Oct 1996 09:19:13 GMT (Paul Crowley) wrote:

>Can I take it that you are now converted to the cause?

There's still the problem of how robust Australopithecines,who were
only slightly bigger than graciles (ca.41 kg versus 37 kg),could deal
with leopards,while graciles couldn't. Then there's the problem of why
robusts apparently lost the ability to use tools for food processing
and took the costly road of a massive masticatory apparatus in order
to crack the shells open with their teeth which,even if you have
enamel as thick as A.boisei,will wear your teeth down long before you
have reached maturity. No enamel cap can resist such an onslaught.

>> The potbelliedness of Australopithecines,as inferred from the
>> cone-shaped thorax and the wide flaring iliac blades,might indicate
>> quite some length of gut. Long guts are generally not associated with
>> easy digestability.

>It is somewhat far-fetched to make conclusions about gut dimensions
>and structure from general abdominal shape.

Who's calling the kettle black? As if your speculations have so much
more substance.
A longer,wider gut needs more space.This will influence the size and
shape of the trunk. Why do you think gorillas have such pronounced

>It would follow from your argument that the main hominid line changed its diet drastically
>at some later point. There is no indication of this anywhere.

There's Ardipithecus ramidus with thin enamel and post-canine
dentition significantly smaller than A.afarensis.
A.afarensis with thick enamel and large postcanine dentition
(Megadontia Quotient=1.30)
Australopithecus boisei with hyper thick enamel and very large
post-canine dentition (MQ=2.44)
Homo erectus with reduced enamel thickness and reduced size of
post-canine teeth (MQ=0.92)
All this differentiation because of the same diet? Amazing!
What mechanism do you suggest? Genetic drift?

>The teeth of the Robusts are most unusual and highly informative,
>but I suggest that the size of the jaw and of the masseter muscle
>could have origins other than "heavy chewing". The inference is
>too facile and (as with much in PA) a more sceptical attitude should
>be adopted. AFAIK male gorillas do not do a lot of "heavy chewing".
>Their massive jaws need another explanation; it may be for defence
>against predators.

Even if it was for predator defense the same cannot be said of robust
Australopithecines. They had small incisors and lack the large canines
of gorillas. Their postcanine teeth have a morphology that is suitable
for grinding not shearing or perforating.