No New Species
The textbooks are wrong, says ornithologist Robert Zink of the University of Minnesota’s Bell Museum of Natural History. The ground finches may seem to be different species, at least with superficial comparison, but they’re stuck in what he calls Sisyphean evolution. “Species kind of get started, but . . . they never make it to the top of the hill,” Zink says.
In a recent paper in Biological Reviews, Zink helps make the case. “None of these ‘species’ are distinct,” he says. The various ground finches don’t differ significantly in ways that usually differentiate bird species, such as plumage patterns or song. Unlike with discrete species, these features aren’t stable and can vary over just a few generations, depending on weather and food availability. Sequences of their nuclear and mitochondrial DNA show little variation and none of the telltale signs that suggest distinct species.
The circumstances in the Galapagos — frequent interisland travel due to short distances between islands and interbreeding — prevent the finches from truly forming distinct species. It makes more sense to classify the birds as a single species of ground finch with ecologically driven variations, Zink says.