One of the first of many scheduled events to commemorate the bicentennial of Charles Darwin’s birth and the sesquicentennial of Darwin’s On the Origin of Species took place in Irvine, California, this past weekend. Sponsored by the Sackler program of the U.S. National Academy of Sciences and hosted by John C. Avise (right) and Francisco J. Ayala as part III in their annual In the Light of Evolution (ILE) colloquia, the event (entitled Two Centuries of Darwin) included 17 keynote talks divided into four half-day sessions. Three of these sessions dealt with modern scientific evidence on the three forms of selection that Darwin illuminated during his career: natural selection (e.g., in The Origin, 1859), artificial selection (in The Variation of Animals and Plants Under Domestication, 1868), and sexual selection (in The Descent of Man, and Selection in Relation to Sex, 1871). In the fourth session plus an evening plenary, five prominent historians and philosophers of science evaluated the Darwinian legacy. A few of the many highlights from this eclectic set of lectures follow.
Regarding natural selection, Scott Hodges and Dolph Schluter reviewed evidence from plants and animals, respectively, on how selective pressures can promote prezygotic reproductive isolation in “ecological speciation” events that differ quite fundamentally from more traditional staid speciation scenarios in which postzygotic barriers accumulate gradually in allopatry. As phrased by Schluter, such findings demonstrate that “species really do originate by means of natural selection.” Another theme to emerge from this session was the incredible complexity of biological evolution under selection. Sara Via showed how the sexual genome is a heterogeneous mosaic of selected and neutral DNA sequences with distinctive evolutionary dynamics during speciation and varied porosities at the species boundary. Julius Lukes documented cascades of convergent evolution at the molecular level in protists, as well as the accumulation of bizarre genomic features, all of which seem indicative of natural evolutionary processes and contradictory to any notions of sentient design in the remarkable genomes of these single-celled organisms.
Regarding artificial selection, Ed Buckler and Steve O’Brien addressed molecular transformations during the human-mediated evolution of domesticated plants (notably maize) and animals (cats). Fred Allendorf showed how hunting and trophy fishing by humans can generate “unnatural selection” (disfavoring the biggest or best) that differs diametrically from the artificial selection regimes (typically favoring the biggest or best) in traditional crop science or animal husbandry. Frances Arnold discussed a novel form of artificial selection in the modern era. Under “directed protein evolution,” geneticists synthesize and mutagenize alternative forms of specific proteins (such as cytochrome P450s) and then subject them to repeated rounds of artificial selection for particular biochemical functions. A common result is the rapid emergence, in test tubes, of novel molecules (not known in nature) with a wealth of potential applications in fields such as medicine and pharmacology.
Regarding sexual selection, Adam Jones and Stephen Shuster reviewed and contrasted modern thought about mate choice and mating systems with the sentiments that Darwin had expressed in the Victorian era. Patty Gowaty presented a new model on how time constraints on individuals in various ecological and life-history settings might translate into the mating decisions that underlie sexual selection. And William Eberhard reviewed modern evidence on an important aspect of sexual selection—postcopulatory phenomena, including sperm competition and cryptic female choice—that Darwin had overlooked entirely.
Daniel Dennett, Francisco Ayala, Michel Ruse, Elliott Sober, and Robert Richards each addressed the broader Darwinian legacy, 150 years later, from various historical and philosophical vantages. Perhaps the most controversial suggestion came from Richards, who used selected quotations from Darwin’s writings to suggest that Darwin retained for many years a more goal-directed or teleological view on evolution than has commonly been assumed.
In his concluding comments, John Avise reminded the audience that the intent of the colloquium had been not to idolize Darwin (idolatry, or appeal to authority, has no valid place in science), but rather to celebrate Darwin’s pioneering role in launching a revolutionary discipline that continues to grow in its vibrancy and relevance to all of the biological sciences. Proceedings of the ILE III colloquium will be published later this year as a special edited issue of PNAS and as a book from the National Academies Press.