Hibernation in mammals and birds, from its initiation through the long dormancy to the violent arousal, is a controlled process, developed through evolution to permit the animal to escape from an unfavorable environment. The same type of hibernation, using the same basic physiological modification, occurs in mammals which are so remotely related phylogenetically that one must conclude that hibernation developed separately in several groups as the environ mental stress arose. It is not a primitive return to the cold-blooded state indicating a vestigial reptilian type of temperature control, but rather a specialized temperature regulation with precise control of its own.
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