20 April 2018
Douglas Erwin
Department of Paleobiology
National Museum of Natural History
One of the more peculiar facts about evolution is the under-dispersion of organisms in any evolutionary space: cats are cats, pangolins are pangolins, anomalocariids are anomalocariids and never the twain shall meet. Indeed, the very fact that we can recognize and name discrete entities reflects the gaps between them. Why? If Darwin were right, adaptation driven by natural selection should have produced gradual transitions between species. Recognizing that the fossil record yielded little evidence for gradual transitions Darwin claimed the inadequacies of the fossil record were responsible. Some of his critics, including his close friend Thomas Huxley, argued that gaps were a real signal of evolutionary pattern. This debate arose in the early 19th Century and continues (with new evidence, thankfully) today. During the Modern Synthesis of evolution in the 1930s-1950s Dobshansky and others proposed that gaps represented the ecological and environmental structure of adaptive landscapes. Gradual transitions between species (and larger clades) were missing because they were so ephemeral. The discoveries of deep homologies in developmental processes across animals over the past few decades has led to a resurgence of interest in the possibilities that gaps reflect the internal structure of developmental possibility. If the later claim has merit then evolutionary novelties are a real problem which needs explanation. I will argue for the need to distinguish novelty (the formation of new homologous features) from innovation (the ecological and evolutionary success of new attributes).