Mammals are vertebrate animals whose main feature is breastfeeding the period in which females feed their young with milk from their mammary glands and thus protect them and help to ensure their survival. Breastfeeding starts immediately after birth of the offspring and extends until they can get their food alone; the time coincides with the decrease in the expression of the gene coding for the enzyme lactase that is which breaks lactose from milk thus allowing direct use of glucose metabolism of the individual. However, in the case of man, the expression of lactase extends for much of his life. This allows him to continue consuming milk, although it should be noted that that milk comes from different species to his and it is that, to tame cattle the discovery of the milking process meant a breakthrough for the human being, because that way he does not have to sacrifice the animal to obtain a highly nutritious food. This article aims to revise some aspects of the breastfeeding of the different subclasses of mammals, the importance of the milk and how the man has been able to get it from other species of mammals for their own consumption.

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