Why do humans consume milk after weaning?

Throughout evolution, humans have made many discoveries and innovations which have altered our ability to preserve food or enhance our nutritional intake. Examples include marinating, pickling and cooking. Using cow’s milk as a food source is just another clever practice that humans discovered.

The consumption of milk before and after weaning are two different scenarios. Like all mammals, new-born babies consume only milk, usually their own mother’s which they gradually give up, once they are fully weaned onto a mixed adult diet. Cow’s milk is not suitable for infants and is generally not introduced to the human diet until 1 year of age, where it serves as a nutritious food, along with other animal products such as meat, fish and eggs. The benefits of consuming dairy beyond weaning is evident in human evolution. It is estimated that milk drinking began around 7,500 years ago in central Europe and scientists have suggested that it was a survival advantage to be able to continue digesting milk for its rich nutrient content. It is referred to as ‘natural selection’, which resulted in a change in human gene expression that enabled people to continue producing the enzyme to digest milk. The gene to produce lactase, an enzyme involved in milk digestion, is generally ‘switched off’ in mammals shortly after weaning, when they stop consuming milk. However, this genetic adaption means that the gene could stay ‘switched on’ and the trait is seen in parts of the world where dairy farming evolved. Individuals without this genetic trait can still digest smaller amounts of dairy foods and there is a wealth of research which suggests that dairy is a valuable addition of the diet across the life stages.