Biology Reference
In-Depth Information
rels gnaw food, for example, date back to the ancestor of all living and extinct ro-
dents—convergence, in contrast, is independently evolved similarity, often associated
with a specific function and presumably favored by natural selection. Wings of birds and
bats are thus homologous
as forelimbs
and convergent
as wings,
given that their re-
spective closest relatives are reptiles and mammals with front legs that have not been
modified into flight structures. The common ancestor of birds, bats, and insects was a
far more ancient, simpler organism that lacked appendages of any sort; hence, neither
the wings nor limbs of insects are homologous with those of vertebrates.
Homology thus reflects biological
heritage,
manifested as inherited similarities
among organisms, and if the patterns I'd discovered held up to more extensive taxonom-
ic sampling, identical prey-killing modes of boas and pythons implied descent from a
common ancestor. Moreover, since fossils showed that that ancestor lived at least ninety
million years ago, the homologous behavior of extant constrictors had to be that old too.
I was feeling enthusiastic about these preliminary results until someone in class asked
whether anyone else would care—or in more practical terms, why should a granting
agency fund this research? My rejoinder was that textbooks bemoaned the lack of be-
havioral fossils, other than occasional dinosaur trackways and mosasaur bite marks on
ammonites, so comparisons among surviving species might provide new data on such
things. Here was a way, I hoped, of measuring the geologic age of behavior.
22
Gordon scribbled suggestions on the term paper and pointed out a recently published
critique that raised the intellectual stakes for my project. I had just assumed one could
study what animals do in terms of evolutionary history, as comparative anatomists did
with bones and Lorenz had done with the social displays of ducks and geese; I didn't
know that ichthyologist James Atz had asserted that homology was irrelevant because
behavior, unlike anatomy, he claimed, is highly variable and easily modified by exper-
vergence likely explains similarities among all but the most closely related species. I'd
already seen, though, that tail displays and a diet of elongate vertebrates characterized
dozens of Old and New World coralsnakes, and now I found the same constricting be-
havior in several major snake lineages. Since common ancestry was a straightforward
explanation for those patterns, Atz's sweeping criticisms seemed wrong-headed, and I
began developing a dissertation proposal along those lines even as I set about satisfying
other Ph.D. require-ments.
The two-part qualifying exam was a disaster, thanks to my increasingly overt self-con-
fidence and the peculiar culture of graduate education. On five successive mornings I
typed out answers to my professors' written queries, which I found challenging but well
within my grasp. A week later, however, the oral component began with a physiologist
who grumbled, “This isn't fair because you dropped my course, but what are Herbst cor-
puscles?” After it was clear I was ignorant of far more than sense organs in bird knees,
Susan Riechert, my zoology department coadvisor whose in-class drawing of a sharklike
flatworm mouth I'd corrected during our first semester, barraged me with hard-hitting
ecology questions. When she finished, my head was pounding, my stomach in knots. I
couldn't recall simple details of biochemistry, and over the course of three hours things
declined to a humiliating finale. For the “writtens,” Gordon had asked me to discuss six
of twelve pioneer ethologists; I hadn't subsequently looked up the others, so the ordeal
ended as I slunk out the door with him muttering, “Well, you don't know much about
