All mammals including humans feed their infants milk through breastfeeding. The ability to produce milk is a characteristic of mammals. Humans domesticated cattle millenia ago with the supply of milk being a primary reason - in fact, cattle were domesticated before writing was developed by at least 6,500BC with some estimates going back to 8000BC. In fact, they were considered the earliest form of wealth. Early records showed that they were used as draft animals, milk and as a sacrificial animals as well as meat.