Evolution of Lactation in the Mammalian Species

Lactation is a defining characteristic of all mammals, and indeed mammals draw their name from mammae, or mammary glands. The evolution of mammary glands has been the subject of debate since Charles Darwin.

The purpose of this brief review is not to examine all past theories of mammary evolution, but to consider the evolution of the mammary gland in relation to: Modern paleobiology, with especial attention to the mammaliaforms; comparative aspects of mammary development in monotremes, marsupials and eutherians; the evolution of caseins; the evolution of lipid secretion; the evolution of lactose synthesis, and especially the synthesis of the wide array of oligosaccharides found in some milks.