MOUSE – SPRING 2011
Behavior can be plastic enough that it is sometimes hard to think of
behavior as subject to evolution. But like any other phenotype; it has genetic and environmental
(in this case, usually learning) components. Heritability can range from almost zero to almost
one; it just depends on the species and the behavior in question.
Differences Among Populations
– Bird song is a case in point. In many species, different
populations have different songs. The chicks learn those songs from their parents, and they are
not quite hard-wired. If they don’t learn the right songs, of course, they don’t get to mate. The
songs aren’t necessarily genetically programmed, but the ability to learn song certainly is.
Now, human language. Spanish and Cantonese are not genetically programmed, and children
can learn either language with ease. Linguistic ability is probably partly genetic and partly
environmental (learned). I have seen a professional linguist sit on a log, use sign language to
communicate with an informant speaking an unknown language, and in half an hour, be able
to carry on a full-blown conversation. He was trained, of course, but he also ‘had the gift’.
We can have different degrees to which a behavior can be learned or modified. Marsh wrens
) from Western North America can learn about 100 song types, but
marsh wrens from Eastern North American can handle only about 50. It turns out that the
“song control nuclei” in the brain are larger for the western members of the species.
– We can study the phylogenetic pattern of behavioral evolution. The
standard strategy is to devise a phylogeny, based on some other set of characters than the
behavioral characters under study, and then to map the behavioral characters onto that
phylogeny. Needless to say, we need a really good starting phylogeny to make it work.
Prum has done this for male manikin birds, using the morphology of the syrinx (the vocal
apparatus). Nowadays, we might use molecular markers to do the same thing, but the point
is that we start with a good phylogeny of the group. This group has variable and highly
evolved mating behavioral traits. By mapping them on the phylogeny, Prum:
Traced the pattern and developmental order of 44 behavioral traits within the clade. He
discovered that complex behaviors were derived from simpler, more primitive behaviors,
as elaborations; almost nothing became “more simple” as evolutionary time went on.
He also discovered that some of the behaviors were augmented by morphological changes.
For example, detailed color patterns on wings, were associated with particular display