Recent evidence for the exon theory of genes.

I provide a history of the Exon Theory of Genes, a theory that holds that introns are extremely ancient characteristics of genes and that early genes were created through the intron-mediated shuffling of exons. The theory has existed since the late seventies. An uncompromising version of the theory, in which all introns were considered to be ancient, dominated the early work. However, in the late eighties and early nineties evidence arose that at least some introns are more recently acquired. Due to the previously overly polarized nature of the debate, many results that demonstrated the existence of recent introns have been interpreted by some as evidence that all introns are late, leading some to believe that the theory is no longer a viable theory. However, recent work emphasizes a mixed model, in which some introns are ancient and some new. This model has proven to provide impressive explanatory power for a broad array of observations. Thus, this moderated form of the Exon Theory of Genes still offers a coherent picture of the origin and evolutionary history of the intron-exon structure of eukaryotic genes.