All of this interbreeding upsets the conventional notion of species as discrete, inviolable entities. Moreover, some scientists and conservationists warn that hybridization will degrade biodiversity as unusual species are lost to genetic homogenization. Partly scientists fear hybrids will be less fit than organisms that have evolved in place over eons. And often that is true, but the problem solves itself over time as hybrids lose out in the competitive race for survival. Sometimes, however, the hybrids arefit. Gradually they outcompete distinctive strains and species, wiping out biological diversity that has evolved over millennia. Often it is a common generalist species that swamps and essentially obliterates a rare, specialized and localized species. Many biologists view such occurrences as a net loss of biodiversity. “Hybridization is one of the overlooked but clearly very, very important causes of species’ going extinct,” says Stuart Pimm, professor of conservation ecology at Duke University. “Hybridization is a major problem. It comes from our moving species around, it comes from our changing habitat.”