With the Darwin celebrations gaining momentum, it is worth noting an acknowledgment of error in the great man's thinking. The Press Release says: "Study shows Darwin was wrong about the origins of chickens" and this was echoed in some media reports. Darwin wrote he was confident that the domestic chicken was descended from the red junglefowl, but this turns out to be incorrect.
The yellow legs of chickens reveal their hybrid origin
The clue is in the yellow leg colouration which links to a genetic marker. This marker is not present in the red junglefowl but it is found in the grey junglefowl. The inference is that domestication involved hybridisation. Co-author Greger Larson said:
"Darwin recognized the importance of studying domestic animals as a model of evolution and this insight has proved enormously influential. The ironic thing is that he believed that dogs were hybrids of several wild ancestors but that chickens only had one, and he was wrong on both counts."
Why are these matters worthy of note? Not because Darwin happened to be wrong in his judgment in this matter, because new knowledge has come about with new evidence. We can be confident that Darwin would have changed his mind in the light of this research.
Rather, it is worthy of note because it contrasts strongly with far more important errors Darwin made that are not being brought to the attention of the public. He confused artificial and natural selection; he grossly exaggerated what natural selection is able to do; he assumed variation has no limits; he advanced the concept of common ancestry despite numerous evidences of discontinuity; he dabbled with inheritance by pangenesis (which we don't hear a lot about nowadays); and tried to present embryology and early development as evidence for his theory. We are not confident that Darwin would have changed his mind in the light of new evidences relating to these issues, because Darwin was primarily deductive in his thinking. He was not an empiricist who saw science developing by the testing of hypotheses but be brought a theoretical model to the data and explored 'best fit' scenarios. This approach he learned from Charles Lyell, who did much the same for geological science in his Principles of Geology. We have moved beyond Lyellism in the Earth Sciences - it is time we moved beyond Darwinism in the biological sciences. (For more on moving beyond Darwinism, go here.)
Identification of the Yellow Skin Gene Reveals a Hybrid Origin of the Domestic Chicken
Eriksson J, Larson G, Gunnarsson U, Bed'hom B, Tixier-Boichard M, et al. (2008)
PLoS Genetics, March 2008, 4(2): e1000010 | doi:10.1371/journal.pgen.1000010
Abstract: Yellow skin is an abundant phenotype among domestic chickens and is caused by a recessive allele (W*Y) that allows deposition of yellow carotenoids in the skin. Here we show that yellow skin is caused by one or more cis-acting and tissue-specific regulatory mutation(s) that inhibit expression of BCDO2 (beta-carotene dioxygenase 2) in skin. Our data imply that carotenoids are taken up from the circulation in both genotypes but are degraded by BCDO2 in skin from animals carrying the white skin allele (W*W). Surprisingly, our results demonstrate that yellow skin does not originate from the red junglefowl (Gallus gallus), the presumed sole wild ancestor of the domestic chicken, but most likely from the closely related grey junglefowl (Gallus sonneratii). This is the first conclusive evidence for a hybrid origin of the domestic chicken, and it has important implications for our views of the domestication process.
Study shows Darwin was wrong about the origins of chickens, EurekAlert, 29-Feb-2008
Highfield, R., Darwin was wrong about (chicken) evolution, The Daily Telegraph, 29 February 2008.
Darwin C., 1868. The variation of animals and plants under domestication. London: John Murray. Volume 1, Chapter VII, Fowls, 236-237.
From the extremely close resemblance in colour, general structure, and especially in voice, between Gallus bankiva and the Game fowl; from their fertility, as far as this has been ascertained, when crossed; from the possibility of the wild species being tamed, and from its varying in the wild state, we may confidently look at it as the parent of the most typical of all the domestic breeds, namely, the Game-fowl.
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