Evolutionary Response to Global Climatic Change

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Abstract
From existing evidence for short- and long-term evolutionary change in relation to climate, it must be concluded that such evolutionary change can take place. At the same time there is clear evidence that such evolutionary change does not necessarily take place, even if the environmental conditions, and therefore the conditions for selection, are appropriate. Where such evolution does occur there appear to be definite limits to what takes place. Similar evidence is forthcoming from situations where artificial selection has been applied. The explanation appears to be that all evolution depends on the occurrence of appropriate variability, and that for various reasons this is not always present in natural populations. This picture is confirmed by an examination of the historic evidence for changes in species distribution in relation to past climatic changes. Generally species have behaved, from an evolutionary point of view, in a conservative manner, and have responded to climatic change not by evolution, but by migration. Although some evolution in relation to climatic change may take place, we must not therefore presume that its power will be unlimited in relation to future climatic change. As a result, and because the natural migration of species is now very restricted, we should expect considerable numbers of extinctions, unless we take special steps to transfer artificially whole groups of species from one geographic region to another.

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