Final answer:
Lactase is the enzyme that enables the digestion of lactose, commonly found in milk, beyond infancy. The persistent production of lactase in adults is an evolutionary adaptation that occurred when dairy agriculture became prevalent, particularly in European populations, where the consumption of milk provided an advantage.
Step-by-step explanation:
The enzyme that allows humans to digest something our ancestors normally would have ingested only as infants is called lactase. This enzyme is responsible for breaking down lactose, which is found in milk. The development of lactose tolerance in adult humans is an adaptation to dietary changes—specifically, the consumption of dairy products that began with the domestication of cattle during the agricultural revolution.
The ability to produce lactase into adulthood emerged and spread particularly in European populations, where those with a genetic mutation allowing continuous lactase production had an evolutionary advantage. This is because dairy products became a consistent food source, providing essential nutrients like vitamin D and calcium.
This enzyme's function and the evolutionary changes in human populations exemplify how lifestyle changes, such as the shift from a hunter-gatherer to an agricultural society, can lead to genetic adaptations. Historically, most adult mammals, including humans, naturally stopped producing lactase after infancy; however, due to the persistence of lactase production into adulthood in certain human populations, a significant number of adults are now able to digest lactose.