Darwin gets a boost by a new study citing evidence for the environmental basis of natural selection.

Amidst the hubbub of pundits and policy-makers bickering over evolution, intelligent design and creationism, a group of researchers working at Vanderbilt University have published the results of a wide-ranging study in the online version of the Proceedings of the National Academy of Sciences that provides evidence for an environmental basis for the origin of species, rather than a random series of genetic mutations, supporting the theory of natural selection.

“Since science never conclusively proves any theory, we cannot claim that our study does so,” said Daniel Funk, assistant professor of biology at Vanderbilt and the main author of the study. “However, it is highly consistent with an integrated evolutionary perspective.”

Several studies of individual species—such as cichlid fish in Lake Victoria—support Darwin’s hypothesis of natural selection as a direct cause of speciation. Funk’s study is the first to look for a general pattern across many species. The team found existing data on eight different animal and plant groups that tracked interbreeding capacity over time and compared it with data on environmental factors such as habitat and diet.

Darwin introduced the theory of natural selection to account for similar organisms that develop differently over time when placed in disparate environments. Famously, finches in one part of the Galapagos Islands evolved traits that corresponded to the exigencies of their habitat, while finches in other areas evolved another set of traits.

However, many evolutionary biologists have held that natural selection plays only a limited role in speciation, or the creation of new species, according to Massimo Pigliucci, professor of ecology and evolution at SUNY-Stony Brook.

“The majority position over the last several years has been that speciation events don’t need to be driven by natural selection, that is, that ecology has little to do with it,” Pigliucci said.

According to this theory, most mutations would be neutral, or at least would have little effect on an organism’s success within its ecological environment. Some mutations, however, may alter the organism’s reproductive system, causing fluctuations in gene transmission over very long periods of time. These shifts could eventually result in a novel genetic makeup and, consequently, a new species.

But a dissenting group of biologists, including Funk, sought to explain speciation through natural selection, arguing that systematic responses to environmental demands drive the formation of species. Since the inability to interbreed with geographically disparate members of the same species defines speciation, their studies have compared a particular organism’s capacity to interbreed with its adaptation to an environmental niche.

“We predicted that if natural selection promotes speciation, there should be a positive association between these variables, and that this association should be observed across these eight diverse animal and plant groups,” said Funk. “Our findings supported this prediction and suggested that the observed association was highly unlikely to be due to chance.”

Originally published March 6, 2006

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