Mammalian evolution promotes survival advantage
Paleontologic evidence suggests that vertebrates evolved gradually from deuterostome ancestors about 500600 million years ago, and many innovations were retained in their evolutionary descendants (Smith & Davidson 1994). About 190 million years ago the mammary gland evolved as a consequence of the newborn receiving nutrients from secretions of the maternal ventral thorax/abdomen. This favoured maternal infant interaction (Blackburn 1993). Evolutionary success was determined by an ability to reproduce, to cope with the environment, to reach the reproductive period and to assure long term survival of offspring (Goldman et al 1998). In an evolutionary context, milk allows the infant to mature to a sexually-active adult better able to cope with the environment.