EVOLUTION: A Thermal Puzzle

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Science  17 Nov 2000:
Vol. 290, Issue 5495, pp. 1261e-1263e
DOI: 10.1126/science.290.5495.1261e

It has been proposed that endothermy in birds and mammals arose through beneficial increments in the resting metabolic rate. Bennett et al. test this thermoregulatory hypothesis by quantitating the effects of increasing three- to four-fold the metabolic rate of an ectotherm by feeding Varanus lizards a very large meal. This elevated metabolic rate—similar to that of a hedgehog, an endotherm of the same size—was maintained for at least 24 hours postprandially, but had very little impact on increasing or stabilizing body temperature. Without a thermoregulatory benefit, the increase in metabolic rate is a net cost to the animal, suggesting that the turbocharged metabolism characteristic of endothermic organisms initially arose for some other, as yet obscure reason and that thermoregulation was a subsequent, secondary benefit. — AMS

Evolution 54, 1768 (2000).

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