Clades versus clones in evolution: why we have sex

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Science  24 Oct 1975:
Vol. 190, Issue 4212, pp. 382-383
DOI: 10.1126/science.1179215


Sexual reproduction predominates among organisms mainly because most evolutionary change is concentrated in speciation events, and asexual species cannot speciate in the normal sense. Asexual clones seldom diversify rapidly enough to overcome normal rates of extinction. In contrast, phylogenetic groups of sexual species (clades) commonly develop broad, heterogeneous adaptive zones rapidly enough to ensure survival.