Yale scientists use three-legged stool for better view of evolution

Until recently, two “styles of thinking” have dominated the study of evolution: “Population thinking”, where adaptation and the origin of species are driven at the population level, and “Tree thinking”, which views species in a hierarchical structure. In a commentary published in the Journal of Experimental Zoology, Yale researchers argue that the recent advent of “homology thinking” has emerged as an important “third leg” of the stool of evolutionary biology. Homology is the existence of shared ancestry between a pair of structures, or genes, in different species. A common example of homologous structures in evolutionary biology are the wings of bats and the arms of primates.

Expanding on the work of Marc Ereshefsky, professor of philosophy at the University of Calgary, researchers at Yale explain what homology thinking can mean for biology from the perspective of a developmental genetic approach.

“Of course population and tree explanations have their role in evolutionary biology and beyond, but they refer to quite general attributes of organisms and provide a rather abstract picture,” said Gunter Wagner, lead author. The researchers noted that homology thinking recognizes that organisms consist of sub-systems - such as body parts - that develop individually in terms of development, genetic variation and function.

“With only two perspectives, each has its own agenda with little that can be said to assess the relative importance of the other”, said Wagner, a Professor of Ecology and Evolutionary Biology and member of the Yale Systems Biology Institute. Introducing homology thinking has added a third perspective on evolutionary processes, where any two theoretical perspectives can be viewed from the theoretical commitments of the third perspective. “That fact can help ease the tendency for polarization among our ideas”, noted Wagner. “Homology can provide new insights to evolutionary change through the origin, loss and modification of novel body parts between species”.