Many plant species have accepted the trade-off between the benefits of greater self-reliance and the disadvantages inherent in inbreeding to switch from outcrossing to self-fertilization. However, little is known about the speed at which this happens, sayrnStephen Wright of the University of Toronto in Canada and his colleagues.rnBy sequencing 39 nuclear genes from specimens of the selfing Capsella rubella and its outcrossing progenitor Capsella grandiflora, they estimate that the move in this species happened within the past 20,000 years. This is consistent with it occurring since the last glacial maximum, after which agriculture spread across Europe, producing a situation favourable to plants more capable of colonization - one of the advantages of selfing. Natural selection for guaranteed reproduction can thus lead to major changes and speciation over short periods of time, the authors speculate.
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