Memory flies sooner from flies that learn faster.

Abstract

Learning, like any phenotypic trait, is expected to evolve under natural selection. A prerequisite for evolutionary change is heritable variation in learning in natural populations. It is customary in evolutionary biology to think of genetic variation in a complex trait such as learning ability in terms of a so-called “bell curve” or normal distribution (1) (Fig. 1). Most individuals are average at learning, although some may be very good and some very bad. Such a pattern of variation, if it has a genetic basis, would involve the action of multiple, probably many, genes each making a small contribution to variation in learning ability. Consistent with this view, decades of research on learning mutants of the fruit fly Drosophila melanogaster have characterized a large number of genetic loci involved in learning and memory (2, 3). Likewise, results of artificial selection on lines derived from natural populations of Drosophila (4) as well as quantitative genetic studies of other organisms [e.g., honey bees (5)] are all suggestive of a pattern of continuous genetic variation in learning and memory. In a recent issue of PNAS, work reported by Mery et al. (6) suggests that learning and memory in D. melanogaster in nature may be distributed quite differently, specifically as distinct types defined primarily by allelic variants of a single gene (Fig. 1). Their findings provide the first clear-cut evidence in non-human animals of a naturally occurring genetic polymorphism in learning and memory.