A opinião de Mayr sobre Darwin na questão da especiação

A Century of Evolution: Ernst Mayr (1904–2005)

Mayr’s view of Darwin: was Darwin wrong about speciation?

JAMES MALLET*

Galton Laboratory, Department of Biology, University College London, 4 Stephenson Way, London NW1 2HE, UK

Received 30 January 2008; accepted for publication 30 May 2008

We commonly read or hear that Charles Darwin successfully convinced the world about evolution and natural selection, but did not answer the question posed by his most famous book, ‘On the Origin of Species . . .’. Since the 1940s, Ernst Mayr has been one of the people who argued for this point of view, claiming that Darwin was not able to answer the question of speciation because he failed to define species properly.Mayr undoubtedly had an important and largely positive influence on the study of evolution by stimulating much evolutionary work, and also by promoting a ‘polytypic species concept’ in which multiple, geographically separated forms may be considered as subspecies within a larger species entity. However,Mayr became seduced by the symmetry of a pair of interlocking ideas: (1) that coexistence of divergent populations was not possible without reproductive isolation and (2) reproductive isolation could not evolve in populations that coexist. These beliefs led Mayr in 1942 to reject evidence of the importance of intermediate stages in speciation, particularly introgression between hybridizing species, which demonstrates that complete reproductive isolation is not necessary, and the existence of ecological races, which shows that ecological divergence can be maintained below the level of species, in the face of gene flow. Mayr’s train of thought led him to the view that Darwin misunderstood species, and that species were fundamentally different from subspecific varieties in nature. Julian Huxley, reviewing similar data at the same time, came to the opposite conclusion, and argued that these were the intermediate stages of speciation expected under Darwinism. Mayr’s arguments were, however, more convincing than Huxley’s, and this caused a delay in the acceptance of a more balanced view of speciation for many decades. It is only now, with new molecular evidence, that we are beginning to appreciate more fully the expected Darwinian intermediates between coexisting species.

© The Author. Journal compilation

© 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 3–16.

ADDITIONAL KEYWORDS: ecological races – essentialism – history of science – interspecific hybridization – introgression – nominalism – philosophy of science – species concepts.

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