[Taxacom] orangutan enamel and evolution

[John Grehan]

OK - I included 'orangutan' in the subject so those fed up with the
subject can immediately delete.

 

Recently Vogel et al (2008) published a paper on the functional ecology
and evolution of hominoid molar enamel thickness with respect to the Pan
and Pongo (Journal of Human Evolution). In this paper they confirm the
well known fact that the enamel of Pongo is thicker than Pan,
particularly along the occlusal basin, an area associated with crushing
during chewing. 

 

They state that "the divergent molar characteristics of Pan and Pongo
provide an instructive paradigm for testing hypotheses on the evolution
of molar enamel thickness".

 

They go on to describe the mechanical properties of food in the diet of
each and they confirm predictions that the diet of Pongo is more
resistant to deformation and crack initiation or propagation than that
of Pan. 

 

They conclude in their discussion section that the results are
consistent with hypotheses that posit an adaptive association between
hard foods and thickly enameled molars - which is another way of saying
if you have thick enamel you can crush harder foods.

 

In their section on the evolution of diet in the Hominoidea (humans,
great apes, lesser apes), they say "the conclusions contained herein
have implications for the evolution of diet in the Hominoidea." They
then cite claims that the thick enamel represents a primitive retention
in Pongo while thick enamel is supposed to have characterized the
ancestors of African apes so that their thin enamel represents a
derivation due to selection. 

 

The only problem with this paper (and many others like it) is that it
fails to recognize that there are two different phylogenetic hypotheses
for the origin and evolution of the African apes and Pongo, and each
theory has profound implications for interpreting the origin and
evolution of traits such as enamel thickness. The implications are, of
course, fundamental to human origin because humans, like Pongo, have
thick molar enamel. The idea of that African apes evolved thin enamel
from a thick enameled ancestor is not supported from morphology, but is
a necessary conclusion if the sister group relationship of humans and
chimpanzees is to be accommodated despite the contradictory distribution
of enamel and other characters. The alternative is that the shared thick
enamel of humans and Pongo represents a shared derived character
originating from a unique common ancestor with that feature. 

 

The failure to recognize and discuss the two alternative phylogenetic
theories undermined their stated goal of "testing hypotheses on the
evolution of molar enamel thickness". Instead, they only demonstrate
that if you have thick enamel you are more able to eat hard foods. The
shared thick molar enamel of humans and Pongo is phylogenetically
interesting as it is one of at least 30 other uniquely shared features,
and it is one of about five uniquely shared dental features. Whether one
accepts or rejects the orangutan theory of human origin, that
commonality should be interesting enough to include in morphological
discussions such as this.  

 

John Grehan

 

 

Dr. John R. Grehan

Director of Science and Collections

Buffalo Museum of Science1020 Humboldt Parkway

Buffalo, NY 14211-1193

email: jgrehan at sciencebuff.org

Phone: (716) 896-5200 ext 372

 

Panbiogeography

http://www.sciencebuff.org/biogeography_and_evolutionary_biology.php

Ghost moth research

http://www.sciencebuff.org/systematics_and_evolution_of_hepialdiae.php

Human evolution and the great apes

http://www.sciencebuff.org/human_origin_and_the_great_apes.php