The diagnostic features of man, features that differentiate us from all other mammalian species, can be considered to be the product of the last round of adaptation to a specific environment. At the other extreme are characteristics that we share with all mammals. They too are characteristics that evolved in response to rather specific environmental demands. They are also the adaptations on which all subsequent adaptations, including those distinguishing us as a species, have been based. That is, natural selection acts on established features when a species radiates into a new environment, so that every adaptation arising is based on a precursor or on an old adaptation from the parent species. Not only is the new adaptation based on an old one, but it is also a compromise between the old adaptation and an unachieved ideal, due to the resistance to change that has not been wiped out by natural selection.
KeywordsParental Care Mammalian System Nitrogenous Waste High Body Temperature Scent Gland
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