Combating the Assumption of Evolutionary Progress: Lessons from the Decay and Loss of Traits

Abstract

Contrary to popular belief, evolution is not necessarily progressive. Indeed, traits are often lost or substantially reduced in the process of evolution. In this article, we present several case studies that can be used in the classroom to illustrate both the ubiquity and diversity of cases of trait loss. Our recently acquired knowledge of genetic and developmental processes can provide insight into how traits are gained and lost through evolution. Several practical applications also emerge from studies of trait loss and degeneration, and we focus on those with medical relevance. Examining trait loss also provides perspective on the crucial differences between Darwinian evolution and social Darwinism. We encourage educators to devote greater attention to trait loss in secondary biology and undergraduate evolution courses, and discuss how such information may be best incorporated into evolution curricula.