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Glaciation, An Isolating Factor in Speciation

A. L. Rand
Evolution
Vol. 2, No. 4 (Dec., 1948), pp. 314-321
DOI: 10.2307/2405522
Stable URL: http://www.jstor.org/stable/2405522
Page Count: 8
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Glaciation, An Isolating Factor in Speciation
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Abstract

A number of northern North American birds have a more or less continuous range in which some geographical representatives are further evolved than the subspecies stage, but have not reached the species stage. If these evolved under present conditions they would appear to be cases of speciation without geographical isolation. However, a factor in their history seems to be the glacial period which provided temporary geographical barriers so that fragments of the species had isolation in which to develop. With the retreat of the glaciers these populations met again, and now show various degrees of relationships between that of subspecies and species. Some may be 'species in the making,' but others may be merging.

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