Monday, February 10, 2014

Origin of Species - An Example

How new species arise has been a question at the core of evolutionary theory and a point of challenge for those forces which adhere to an intelligent designer as the source. The idea of a new species arising from a pre-existing one seems to require many simultaneous changes, many of which could prove lethal. Yet in a paper recently published in Cell Reports (1), it appears that the process isn’t all that difficult or rare. Only relatively few genetic changes are needed for the evolution of a new species, even when two divergent populations remain in contact and continue to mate.

The researchers at the University of Chicago analyzed the genomes of two closely related butterfly species, Heliconius cydno and H. pachinus. They found that the initial divergence occurs in a small fraction of the genome, usually related to wing color pattern, which is important in mating and predator avoidance. Once started, however, added changes in other genes rapidly occurred in escalating divergence, usually in neutral regions of the genome.

The divergent regions were shown to be the result of both natural selection and adaptive introgression (the movement of genes through backcrossing of hybrids with parental species, since the hybrid species were still able to mate with parental species). The process of new species creation was shown to be a gradual one, rather than the result of a sudden split between two divergent populations. According to the authors, the mechanism of selection and adaptive introgression in the creation of a new species demonstrates “the link between mircroevolutionary processes acting within species and the origin of species across macroevolutionary timescales,” thus addressing the objection put forth by proponents of intelligent design that evolution explains changes on a micro level but not on a macro level.

How important this type of speciation is to other organisms remains to be seen, but the fact that it can occur in butterflies should send some deniers of evolution back to the drawing board.

1.     Marcus R. Kronforst, Matthew E.B. Hansen, Nicholas G. Crawford, Jason R. Gallant, Wei Zhang, Rob J. Kulathinal, Durrell D. Kapan, Sean P. Mullen. Hybridization reveals the evolving genomic architecture of speciation. Cell Reports, 2013 DOI: 10.1016/j.celrep.2013.09.042