Some clover species have two forms, one of which releases cyanide to discourage nibbling by snails and insects and the other of which does not. A scientist at Washington University in St. Louis found that this “polymorphism” has evolved independently in six different species of clover, each time by the wholesale deletion of a gene. The clover species are in a sense predisposed to develop this trait, suggesting that evolution is not entirely free form but instead bumps up against constraints.
A recent interdisciplinary conference that led to the publication of a special issue of PNAS on domestication raised more questions than it answered. Washington University in St. Louis scientists Fiona Marshall and Ken Olsen, who participated in the conference and contributed to the special issue, discuss some of the key questions that have been raised about this pivotal event in human history.
Did domesticating a plant typically take a few hundred or many thousands of years? Genetic studies often indicate that domestication traits have a fairly simple genetic basis, which should facilitate their rapid evolution under selection. On the other hand, recent archeological studies of crop domestication have suggested a relatively slow spread and fixation of domestication traits. An article in “The Modern View of Domestication,” a special issue of PNAS, tries to resolve the discrepancy.
With the help of modern genetic technology and the resources of the International Rice GeneBank, which contains more than 112,000 different types of rice, evolutionary biologist Kenneth Olsen has been able to look back in time at the double domestication of rice (in Asia and in Africa) and its double “de-domestication” to form two weedy strains. Olsen predicts the introduction of pesticide-resistant rice will drive ever faster adaptation in weedy rice.