The evolution of lactation as a strategy by which mothers can continue to nourish their offspring after birth is of such profound significance that it forms the very basis for identifying a whole class of vertebrates, the Mammalia. Although certain non-mammals also feed their young by maternal secretion of nutrients, it is only the mammals that have developed specific cutaneous secretory organs, the mammary glands. The philogenic origins of these, now highly developed, glands are thought to have arisen from the selective modification of apocrine sweat glands (Mepham, 1987). Divergent evolution has since resulted in wide variations in the number, morphology and anatomy of mammary glands, ranging from the teatless abdominal pouches of egg-laying mono-tremes to the highly-developed udder of the dairy cow capable of remarkable feats of biosynthesis. The present paper considers how evolutionary factors may have shaped the development of human lactation and how these now influence the way in which lactation is affected by environmental variables; primarily the nutrition of the mother.
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