Dubious species?

In "Evolutionary Anthems" ["Biomechanics," 10/03], Adam Summers reports the work of Jeffrey Podos and his colleagues, which suggests that the songs of Darwin's finches might be responsible for the group's rapid speciation. He counts fourteen species, but by my count that is at least one too high. Two of the putative species, the mangrove and the ground finch, interbreed and produce fertile offspring. By, Ernst Mayr's definition, that makes them one species.

Dubious species pervade the world of taxonomy. In particular, songs no more determine finch species than they do human ones. Women who sing in church choirs and men who rap are not members of different species. They might not even ordinarily mate, but they can, so they belong to one species.

Frank Weigert

Wilmington, Delaware

ADAM SUMMERS REPLIES: I would agree with Frank Weigert that where interbreeding

occurs, the existence of separate biological species is called into question. In the case of incipient speciation, however, I think it is more interesting to understand the trajectory of the evolutionarily salient milts rather than the progress of the biotic isolating mechanisms.

Regardless of species, or subspecies, count, I find it fascinating that the song that enables members of a population to recognize one another is ultimately affected by diet. The song can therefore serve as an honest signal, passed along prior to mating, about functional capacities such as the ability to process certain foods.

AMENDMENT: Many readers noticed the continental mix-up, due to an editing error, in Adam Summers's column "Like Water Off a Beetle's Back" (February 2004). The southern tip of Africa is the Cape of Good Hope, not Cape Horn.

COPYRIGHT 2004 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning