Cimino&Ghiselin-tmpZXYZ:Template Proceedings_1.qxd.qxd

186 PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES
Series 4, Volume 60, No. 10
approaches had little new to offer except, sometimes, speculations that filled in gaps in their data.
There was an opportunity to extend the synthesis by using new materials and an improved
methodology. Molecular biology was particularly promising, especially when rapid sequencing
techniques for proteins and nucleic acids became available. The new molecular techniques largely
supplanted older ones such as immunology, so calling this a “molecular revolution” is a bit hyperbolic.
What might be called a “restoration” rather than a “revolution” was the rediscovery of the
importance of branching sequences in addressing problems of evolutionary history. There had been
too much emphasis on arranging the organisms on the basis of how primitive and advanced they
are and of how one group has given rise to another. The problem-solving situation called for placing
the branches of a phylogenetic tree next to their closest relatives, and asking how the various
lineages have diverged.
One of us (M.G.) did his doctoral research on the reproductive systems of opisthobranch gastropods,
a group of mollusks that is closely related to the air-breathing snails and slugs called pulmonates.
The change from snail to slug has occurred in many separate lineages of opisthobranchs
and in several of pulmonates as well. “Parallelism” is the technical term for such an evolutionary
pattern, in which several closely related lineages undergo the same basic modification. It is akin to
what is called “convergence” in which initially different organisms become increasingly alike, usually
because they occupy the same habitat or have the same way of life. Hummingbirds and hawkmoths
provide a good example of convergent evolution. From a distance they look very much alike,
but one does not have to be an expert to see that the resemblances are only superficial. Parallelism
is much more difficult to recognize, for the resemblances, among slugs for example, can be quite
detailed and extend to many parts of the body. Therefore parallel evolution poses an interesting
methodological challenge. One solution to that problem is to find parts of the body that show divergence,
rather than parallelism—in other words parts that become different instead of changing in
the same basic way. The reproductive system evolves more or less independently of the rest of the
body and is not much affected by the changes that are involved in transforming a snail into a slug.
The resulting phylogenetic tree left many questions open, but it did have some interesting
implications. Among these was the fact that the various lineages of opisthobranchs tended to specialize
in feeding upon a particular kind of food, or, what amounts to much the same thing, to having
the same basic feeding mechanism. Gastropods in general move around quite slowly, but they
are adept at finding, subduing, and processing “difficult” food items. The oral cavity usually contains
a tongue-like strap called a radula, covered with hard teeth, which is very effective in cutting
and tearing. Opisthobranchs tend to specialize on food items that other animals leave more or less
alone. A fair number eat other opisthobranchs. Some eat macroscopic or filamentous algae. Many
feed upon sponges. How that relates to natural products chemistry was not obvious until D. John
Faulkner of the Scripps Institution of Oceanography entered the picture. He and his collaborators
had been studying the natural products chemistry of many marine organisms, including opisthobranchs,
and posed the “which came first” question that was discussed earlier in this introduction.
We found evidence that supported his idea that use of defensive metabolites preceded the loss of
the shell. Not only that, the use of chemical defense turned out to be even more widespread and
various within the group than had been anticipated. We concluded that chemical defense has been
the “driving force” behind the large-scale evolution of the group (Faulkner & Ghiselin, 1983).
Meanwhile, at Naples, where we would later join forces, G.C. had also become interested in
the chemistry and biology of mollusks. He did his doctoral thesis on the black pigments called
melanins of the cephalopod Sepia officinalis. Later he worked extensively on other marine animals
including sponges. Toward the end of the 1980s he actively collaborated with Spanish biologists,
notably the evolutionary ecologist Joandomenec Ros, and shifted his research program to opistho-