tgamble

A poster on another forum wrote:

"I wanna make sure you know what makes us different than apes. We have smaller teeth, K-9's, we have no sagittal crest (used for chewing strong), and have more of a chin.

A. Afarensis had a hint of a sagittal crest (apelike), with large teeth (apelike), and large K-9's. Next up is Africanus. This species has NO crest (like us), with LARGER K-9's than Afarensis, and larger back teeth (apelike). Next is P. Robustus. From the small specimens found, Robustus has a definite sagittal crest again (even though the previous species lost it), and large back teeth.

My problem with this is that the species' go from having very apelike traits, to becoming more humanlike, then back to having the apelike traits again. If I misunderstand or misinterpret this evidence, then I'd be glad to know."

He's not a creationist really and rejects creationism so he seems reasonable.

The only response I can come up with is the fact that he's looking at only a couple of specimens and a couple of features. I've already checked talkorigins. Is there anything I should add? Thanks.

gallo

P. robustus is not believed to be ancestral to modern humans in most family trees. There is also some discussion as to whether P. robustus descended more directly (through P. aethiopicus) from A. afarensis, or from A. africanus (also through P. aethiopicus). P. boisei is a comtemporaneous species that also had a sagital crest.

Besides, the crest depends a lot on diet. Large muscles have large anchors. It is one reason why big people are "big boned."

[ May 06, 2002: Message edited by: gallo ]</p>

Dr.GH

You might use the following sites, and refer your correspondent to them as well.

<a href="http://www.mnh.si.edu/anthro/humanorigins/faq/Encarta/encarta1.htm" target="_blank">Encarta Human Origins web page</a>

and

<a href="http://www.becominghuman.org/" target="_blank">Becoming Human</a>

Ergaster

I'm not quite sure how to address this, because the context of your discussion is not clear--what, exactly, is your correspondent trying to argue?

One could approach this from a couple of directions, depending on the specifics of the discussion.

First: he's right. Humans are different from other apes. But then, each ape is different from any other ape--that's how we can tell us apart. (:

But the differences are imposed upon a deeper similarity, and these differences are likely due to our different adaptations and their consequences. Humans have a different diet from other apes, and we mechanically process most of the food we eat (chop it, cook it, etc.), so our chewing apparatus (teeth, chewing muscles and their anchors) has gotten smaller (btw--tell your correspondent that they are "canines". K-9 was a stupid movie, I think...). However, those are not actually the features that make us apes in the first place.

The second direction is that of the fossils: there are a lot more hominin species than the ones listed here, and the ones you list do not make any sort of evolutionary progression. So, while it is true that Australopithecus afarensis, A. africanus, and Paranthropus robustus have different masticatory adaptations from each other and from us, the random selection of three out of a possible 10 or so species of non-Homo hominins is basically meaningless as far as trying to infer evolutionary trends.

[ May 07, 2002: Message edited by: Ergaster ]</p>