Genomic catastrophism and the origin of vertebrate immunity.

Genomic catastrophism is the belief that unique genetic events, unlike those observed in recent evolutionary history, played a key role in the origin of vertebrate adaptations. Catastrophist hypotheses have been particularly popular is accounting for the origin of vertebrate specific immunity. Two major such hypotheses involve genome duplication by polyploidization and horizontal gene transfer. Recent analyses lead to decisive rejection of the widely cited hypothesis that the vertebrate genome underwent two rounds of genome duplication, and theoretical considerations suggest that genome duplication is unlikely to lead to new adaptive advances. Likewise, the evidence that key elements of the vertebrate immune system arose by horizontal transfer from a bacterium or by incorporation of a transposable element into the vertebrate genome remains relatively weak. Thus, at present, a uniformitarian view of the origin of the vertebrate immune system seems more reasonable, especially given the longer time-frame for vertebrate evolution indicated by molecular data.