Bees, dogs, and cattle have all provided interesting evolutionary stories this week. Now it goes to the chickens: A study by Jonas Eriksson and colleagues finds that introgression from grey junglefowl contributed to the gene pool of domesticated chickens:
This study contradicts the assumption that the red junglefowl is the sole wild ancestor of the domestic chicken  and provides the first conclusive evidence that other species have contributed to the domestic chicken genome. We therefore propose that the taxonomy of the domestic chicken should be changed from Gallus gallus domesticus to Gallus domesticus to reflect the polyphyletic origin of chicken . The emerging technologies for total genome resequencing can be readily employed to determine if other parts of the chicken genome also originate from other species of junglefowls. Such regions are expected to be enriched for functionally important variants, like yellow skin, because neutral sequences should have been diluted out during the extensive back-crossing that must have taken place after introgression. It is possible that the introgression of yellow skin was facilitated by the fact that it resides on a microchromosome (only 6.4 Mb in size) with a high recombination rate, which reduces the amount of genetic material affected by linkage drag.
The need to reduce linkage to possibly disadvantageous genes around an introgressive allele is an important thing to consider, although breaking such an allele down to a 6 Mb block wouldn't take an terribly long time. The real question is why this trait in particular was brought into chickens -- whether it was linked to desirable pelage characters, or whether it may have had other advantages in survival or productivity under domestication.
These two species are not known to hybridize in the wild.
(via Blog Around the Clock)
(also Greg Laden)
Eriksson J, Larson G, Gunnarsson U, Bed'hom B, Tixier-Boichard M, Strömstedt L, Wright D, Jungerius A, Vereijken A, Randi E, Jensen P, Andersson L. 2008. Identification of the Yellow Skin gene reveals a hybrid origin of the domestic chicken. PLoS Genet 4:e1000010. doi:10.1371/journal.pgen.1000010