Chapter 18 - Gene Transfer Through Introgressive Hybridization: History, Evolutionary Significance, and Phylogenetic Consequences

Abstract

This chapter focuses on the history, evolutionary role, and the phylogenetic impact of gene transfer through introgressive hybridization. The rudimentary understanding of hybridization and heredity demonstrated by ancient humans was largely lost until late in the 17th century. The possibility of gene transfer through introgression was not recognized until early in the 20th century, but its evolutionary importance has been debated ever since. The role of introgression in adaptive evolution is more difficult to assess, however, because advantageous alleles spread quickly, making it difficult to catch the introgression of favorable alleles in action. Nonetheless, molecular marker surveys indicate that introgression is widespread in both plants and animals. Thus, horizontal gene transfer and hybridization represent viable alternative explanations for discordance between gene lineages and organismal pedigrees. The model therefore, predicts that selection in the hybrid zone will be largely exogenous, that diagnostic characters should exhibit clinal variation if the zone occurs along an ecotone, and that only a subset of favored hybrid genotypes are likely to be common in the hybrid zone.