News of the WeekSPECIATION

Mexican Pairs Show Geography's Role

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Science  20 Aug 1999:
Vol. 285, Issue 5431, pp. 1190
DOI: 10.1126/science.285.5431.1190a

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By examining 37 pairs of closely related forest species, one from each side of the arid Tehuantepec barrier, a lowland area on Mexico's Isthmus of Tehuantepec, a team reports on page 1265 new evidence that such geographic barriers are the major force driving the formation of new species. In every case it appears that the geographic barrier, rather than any difference in ecology, was the critical factor in speciation, isolating the original populations so that they accumulated genetic differences and eventually became unable to interbreed.