The Origin of Natural Selection

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Science  07 Apr 2006:
Vol. 312, Issue 5770, pp. 21
DOI: 10.1126/science.312.5770.21b

The initial stimulus for Darwin's insight into natural selection as the engine of speciation and evolution is often believed to be the radiation of the Galapagos finch. In fact, his thoughts were triggered by the mockingbirds of the endemic genus Nesomimus, which exhibit a variety of allopatric forms on the islands of the same archipelago. Although the finches have been studied intensely by generations of evolutionary biologists, the mockingbirds have suffered a benign neglect. Darwin's view was that the Galapagos mockingbirds, which were recognized as three species on the basis of the Beagle specimens (a fourth being added after his death), had descended from a single colonization event perpetuated by wayfarers from Chile or Argentina.

Arbogast et al. have tested this view by analyzing mitochondrial DNA sequences. The molecular phylogeny indicates that the Galapagos mockingbirds are indeed monophyletic, but that their closest relatives in the genus Mimus are now found in North and Central America, rather than the nearest part of the mainland (Ecuador), and that Nesomimus appears to belong within the ancestral genus. Their analysis also illuminates the finer-grained relationships amongst the Galapagos mockingbirds, revealing the wind-aided routes by which they diversified and how their history compares to that of the finches. — AMS

Evolution 60, 370 (2006).

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