Wednesday, February 27, 2013

A binder full of hominids

Today, students in my Physical Anthropology class did their hominid phylogeny lab.  They were confronted by this cast of characters (from left: Australopithecus afarensis, A. africanus, Paranthropus aethiopicus, Paranthropus boisei, Homo habilis, and H. erectus):

The students' task was to make a series of observations on these skulls, record them, and then use their results to create hypotheses about the phylogenetic relationships among them: how closely or distantly they're related, and who is most likely ancestral to whom.  The observations involved were:
Presence or absence of sagittal crest
Presence or absence of nuchal crest
Rounded or angular occipital area
Overall length of skull
Overall width of face
Maximum width of premolars
Maximum width of molars
Maximum height of brow ridge
It was nice to see the students going around the lab, moving from skull to skull, making their observations and helping each other out.  The real point of the exercise is not whether they come up with the "right" answers (do even the experts know them?).  It's that for a little while, they are engaged with real-world data, or at least as close as we can to it.

And they discover that the real world can be messy. Some of the measurements are fairly straightforward, such as the length of the skull.  But some, such as molar width, are not always so easy, due to the condition of the fossils.  Some of the observations are about deciding whether a feature is present or not.  Sagittal crests are pretty easy to spot, but nuchal crests seem to give them more trouble and I could hear them arguing about it.  Perhaps most perplexing of all is the occipital region: is it rounded, or is there some angularity to it?

I tried to help them by putting out a male orangutan with very clear sagittal and nuchal crests, but it didn't sound like it helped much.  I also suggested that if they find themselves looking at a skull and wondering whether some feature is there or not, it probably isn't.  That may not have helped much either.

For all the above reasons, this is my favorite lab exercise.  We'll see what happens when they turn in their completed assignments next week.

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