Thursday, 12 February 2015

Darwin's Finches - Another Triumph For Science

Evolution of Darwin/'s finches and their beaks revealed by genome sequencing : Nature : Nature Publishing Group

On Darwin Day, it's good to see yet more scientific evidence showing just how robust and unassailable Darwinian evolution is as a scientific theory. This is confirmed paradoxically by a paper which showed he was ever so slightly wrong about the Galapagos Finches. He thought there were only 14 different species, now genetics has shown there are 17.

However, it confirms what Darwin said - they all radiated from a single founder population and the cause of diversity was natural selection. We now have the genetic evidence.

Charles Robert Darwin, FRS (12 February 1809 – 19 April 1882)
The robust nature of Darwin's theory of evolution and how his theory, which was based on the only thing available to him then - morphology - is shown by the way it not only survived the discovery of genes and DNA, about which Darwin knew nothing, but has been hugely strengthened by it.

Compare this to any other branch of science and you will find that few of them survived intact a major scientific discovery and didn't need to be considerably revised and re-written. Even Newtonian physics was overthrown by Relativity as was the 'Law' of conservation of matter, and quantum mechanics has caused a major rethink about how we view elementary particles, atoms and molecules and how they react.

Yet genetics, DNA, our understanding of protein synthesis, our understanding of how eukaryote cells evolved, plate tectonics and Big Bang cosmology has not even dented the basic principles of diversification and the superficial appearance of design by natural selection from inherited variation. Instead, every major discovery has strengthened and confirmed it. Where once physicists thought they could prove the sun and Earth weren't old enough for life to have had enough time to evolve, it was the physicists who were proved to be wrong, and when geologists thought they could prove that related species could not have travelled from one land mass to another because no suitable land bridges existed, the geologists were proved to be wrong.

And even Darwin did not know how inherited variation could be passed on to the next generation nor how variation actually arose in this information, this was shown to be merely a gap in his knowledge, because he didn't know about DNA.

The paper in question, published today in Nature, reveals for the first time the results of full genome sequencing of not only the 14 recognised species of Galapagos finch and a 15th from nearby Cocos Island but also two more closely related species from the Caribbean.

Darwin’s finches, inhabiting the Galápagos archipelago and Cocos Island, constitute an iconic model for studies of speciation and adaptive evolution. Here we report the results of whole-genome re-sequencing of 120 individuals representing all of the Darwin’s finch species and two close relatives. Phylogenetic analysis reveals important discrepancies with the phenotype-based taxonomy. We find extensive evidence for interspecific gene flow throughout the radiation. Hybridization has given rise to species of mixed ancestry. A 240 kilobase haplotype encompassing the ALX1 gene that encodes a transcription factor affecting craniofacial development is strongly associated with beak shape diversity across Darwin's finch species as well as within the medium ground finch (Geospiza fortis), a species that has undergone rapid evolution of beak shape in response to environmental changes. The ALX1 haplotype has contributed to diversification of beak shapes among the Darwin’s finches and, thereby, to an expanded utilization of food resources.

What this paper also shows is how a single gene is mostly responsible for beak shape in this genus, so allowing adaptation to arise quickly by a small number of mutations.

There is no refutation of Darwinian evolution in existence. If a refutation ever were to come about, it would come from a scientist, and not an idiot.

Richard Dawkins (replying to Ray Comfort)
This fact also shows how speciation and diversification is not the aim of the evolutionary process but an incidental consequence of it. A perfectly natural process can have no aim or purpose. As I explained before in Why Species? where I looked at the diversity we see in European finches, adaptive evolution to exploit a new or evolving food source acts to create the conditions where hybrids are at a disadvantage. They will either have an intermediate beak or, for a single gene obeying Mendelian inheritance, some of the offspring will have the 'wrong' beak. Because intermediates can feed on neither the new food source nor the old one and those with the 'wrong' beak will not have the adaptive advantage, they are quickly eliminated and anything which sets up barriers to hybridization will be an advantage. This can quickly push the two populations to complete speciation, incidentally also explaining the lack of intermediates in the fossil record if this occurs very quickly.

But this genome study also revealed another interesting fact - there are actually probably 17 species, not 14 as was thought. One species, Geospiza difficilis, has genomes that places it in three different branches, so it should be counted as three different species. Geospiza conirostris similarly has genomes placing it in two other different branches so should be regarded as two species not one. Genetics has not only proved Darwin's morphology-based conclusions but has proved to be a superior tool for identification of evolutionary sequences and family trees. It also shows that evolution does not always depend on the outward appearance of the individual but that selection can work on 'invisible' factors, maybe at a physiological level, so morphology itself is a relatively blunt instrument.

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