Evolution can make leaps—but how frequently? Photo by Flavio Martins.
Does evolutionary change happen in big jumps, or a series of small steps? The question may seem a little esoteric to non-scientists—how many mutations can dance on the head of a pin?—but it has direct implications for how we identify the genetic basis of human diseases, or desirable traits in domestic plants and animals.
That’s because the evolutionary path by which a particular phenotype, or visible trait, first evolved in a population is closely related to the genetics that underlie the trait in the present. Phenotypes that arose in a single mutational jump will probably remain connected to one or a few genes with large effects; phenotypes that evolved more gradually do so because they are created by the collective action of many genes. So what kind of evolutionary change is most common will determine which kind of gene-to-phenotype relationships we should expect to find.
In an excellent recent review article for the journal Evolution, Matthew Rockman, a biologist with the Department of Biology and Center for Genomics and Systems Biology at New York University, makes the case that the era of genomics has, so far, been much too focused on finding genes of large effect. Fortunately, Rockman also sees the beginnings of a new movement towards acknowledging the importance of small-effect genes—one which may ultimately make genomic association studies more useful.
