Lactational Programming of Infant Behavioral Phenotype

Imagine a magic potion. This potion includes all of your calories and hydration for the day. It has fatty acids for your brain, amino acids for your muscles, and essential vitamins and minerals for your cellular processes. This potion provides immunoglobulins to protect you from pathogens and hormonal cues about your mother and the environment. This potion delivers bacteria that colonize your gut and then continues to provide specialized nutrients for those bene fi cial bacteria. Oh, and one last thing, your mom makes it just for you. This magic potion, of course, is milk. The synthesis of milk by mammary glands is the de fi ning characteristic of our mammalian class. Identifying the composition of milk, and the volume produced, is foundational to understanding lactation strategies in all mammalian taxa. As you are reading this sentence, hundreds of scientists around the world are investigating what exactly milk is composed of (we still don’t know!), how milk is synthesized, and how infants assimilate milk. Most milk science, however, is applied, and our knowledge of milk is primarily pieced together from the dairy industry, cancer research on mammary gland biology, and agenda-driven contrasts of formula-feeding vs. breast-feeding. Much less is known about milk from an evolutionary biological perspective, and a systematic understanding of the magnitude, sources, and consequences of variation in mother’s milk largely eludes us. For example, gross milk