The puzzle of sympatry. Recent evidence supports the notion of sympatric speciation--the rise of new species in the same location--but the reasons for this phenomenon remain elusive.

For centuries, the greatest puzzle in biology was how to account for the sheer variety of life. in his 1859 landmark book, On the Origin of Species, charles Darwin (1809–1882) finally supplied an answer: his grand theory of evolution explained how the process of natural selection, acting on the substrate of genetic mutations, could gradually produce new organisms that are better adapted to their environment. it is easy to see how adaptation to a given environment can differentiate organisms that are geographically separated; different environmental conditions exert different selective pressures on organisms and, over time, the selection of mutations creates different species—a process that is known as allopatric speciation. it is more difficult to explain how new and different species can arise within the same environment. although Darwin never used the term sympatric speciation for this process, he did describe the formation of new species in the absence of geo graphical separation. “i can bring a considerable catalogue of facts,” he argued, “showing that within the same area, varieties of the same animal can long remain distinct, from haunting different stations, from breeding at slightly different seasons, or from varieties of the same kind preferring to pair together” (Darwin, 1859).