|Nosil Lab of Evolutioary Biology, University of Sheffield, UK|
Here's one of those nice little pieces of scientific research that so infuriates creationist loons and sends them into deep denialism or a frenzied casting around for a way to dismiss it because it doesn't support their sacred conclusions.
One of the interesting questions in evolution is, just how predictable is it? Could we rewind the clock say ten million years and get the same result we have today? Or is there so much randomness in the process that small random differences both in the environment and the evolving individual species would add up eventually to major differences? And this of course is assuming that the main or only component of evolutionary change is natural selection and all change is adaptive. But, if random genetic drift is as important as some people think, then evolution could not be predictable except perhaps in conditions of intense selection pressure.
To help understand this a little better, a group from the Nosil Lab for Evolutionary Biology, University of Sheffield, UK, examined the differences in the DNA of a widespread species of Californian stick insect, Timema cristinae. This species has evolved two ecotypes adapted to living on different hillside plants. One with a broad body which lives on broad-leaved plants and one with a long, thin body with a central stripe, adapted to narrow-leaved plants. Although the same species, these can be seen as a species in the process of diverging into two daughter species.
Natural selection can drive the repeated evolution of reproductive isolation, but the genomic basis of parallel speciation remains poorly understood. We analyzed whole-genome divergence between replicate pairs of stick insect populations that are adapted to different host plants and undergoing parallel speciation. We found thousands of modest-sized genomic regions of accentuated divergence between populations, most of which are unique to individual population pairs. We also detected parallel genomic divergence across population pairs involving an excess of coding genes with specific molecular functions. Regions of parallel genomic divergence in nature exhibited exceptional allele frequency changes between hosts in a field transplant experiment. The results advance understanding of biological diversification by providing convergent observational and experimental evidence for selection’s role in driving repeatable genomic divergence.
Víctor Soria-Carrasco, Zachariah Gompert, et al; Stick Insect Genomes Reveal Natural Selection’s Role in Parallel Speciation;
Science 16 May 2014: Vol. 344 no. 6185 pp. 738-742 DOI: 10.1126/science.1252136
I think it says that repeatability of evolution is very low.As expected, they found many genetic differences between the two ecotypes, but they also found a wide difference between what appeared to be the the same ecotype collected from different hillsides. Only 17 percent of their DNA had changed in the same way. This indicates that a lot of the change is initially random and then selection works on that randomness to arrive at the same adaptive change, but by different routes and with different genes.
Andrew Hendry, evolutionary biologist, McGill University, Montreal, Canada
They've actually been able to dig down into the genome and find out a little bit more about [parallel evolution]. [The work] is really starting to give us some mechanistic understanding of the molecular basis of evolution.So the team then transferred members of each ecotype onto the 'wrong' plant and analysed the DNA of their offspring to see how the frequency of different alleles had changed from those in their parents. These shifts would be due to selection pressure with those more advantageous to the parents making them more likely to breed and so increasing in frequency in the offspring with a corresponding decrease in their less-favourable counterparts. The result was a significant increase in those genes associated with differences in the two ecotypes. In other words, in a single generation, selection pressure had pushed the species towards the ecotype normally living on the host plant onto which they had been transferred.
Tim Coulson, population biologist, Oxford University, UK
These results indicate that divergent selection plays a role in repeated genomic divergence between ecotypes. Furthermore, our results suggest that, although repeated evolutionary scenarios (i.e., replaying the tape of life) would likely result in idiosyncratic outcomes, there may be a repeatable component driven by selection that can be detected, even at the genome-wide level and during the complex process of speciation.
Víctor Soria-Carrasco, Zachariah Gompert, et al; op cit
It would be interesting to hear what one of the loons at the Discovery Institute or the Institute for Creation Research has to says on this subject. Here we see not only environmentally-driven speciation in progress but we can see significant change in the frequency allele of key genes involved in this divergence being measurable in a single generation. If this does not constitute experimental evidence for evolution and an observed instance of speciation in progress so far as they are concerned, then it's probable that there is no evidence that they would accept. It's the equivalent of watching a stone fall to Earth while denying that gravity exists.
The only way this can be dismissed as evidence for evolution is simply to ignore it altogether, or to redefine evolution as something other than the standard scientific description of ".. any change in the frequency of alleles within a gene pool from one generation to the nex" (Helena Curtis and N. Sue Barnes, Biology, 5th ed. 1989 Worth Publishers, p.974).
Any creationist up for trying for an explanation? If so, please try to spell correctly and use proper English grammar.
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