Taking flight!

Understanding the origins of novel complex traits, the evolutionary transitions they enabled, and how those shaped the subsequent course of evolution, are all foundational objectives of evolutionary biology. Yet how developmental systems may transform to yield the first eye, limb, or placenta remains poorly understood. Seminal work by Courtney Clark-Hachtel, David Linz, and Yoshinori Tomoyasu published in the Proceedings of the National Academy of Sciences in 2013 used the origins of insect wings - one of the most impactful innovations of animal life on Earth - to provide both a case study and a new way of thinking of how novel complex traits may come into being. This paradigm-setting study not only transformed the way we view insect wings, their origins, and their affinities to other morphological structures; even more importantly, it created entryways to envision innovation as emerging gradually, not somehow divorced from ancestral homology, but through it via the differential modification, fusion, and elaboration of ancestral component parts. In a conceptual universe of descent with modification, where everything new must ultimately emerge from the old, this work thereby established a powerful bridge connecting ancestral homology and novelty through a gradual process of innovation, sparking much creative and groundbreaking work to follow since its publication just a little over a decade ago.