  We propose a simple model for genetic adaptation to a changing environment,
describing a fitness landscape characterized by two maxima. One is associated
with "specialist" individuals that are adapted to the environment; this maximum
moves over time as the environment changes. The other maximum is static, and
represents "generalist" individuals not affected by environmental changes. The
rest of the landscape is occupied by "maladapted" individuals. Our analysis
considers the evolution of these three subpopulations. Our main result is that,
in presence of a sufficiently stable environmental feature, as in the case of
an unchanging aspect of a physical habitat, specialists can dominate the
population. By contrast, rapidly changing environmental features, such as
language or cultural habits, are a moving target for the genes; here,
generalists dominate, because the best evolutionary strategy is to adopt
neutral alleles not specialized for any specific environment. The model we
propose is based on simple assumptions about evolutionary dynamics and
describes all possible scenarios in a non-trivial phase diagram. The approach
provides a general framework to address such fundamental issues as the Baldwin
effect, the biological basis for language, or the ecological consequences of a
rapid climate change.
