Question

Most people are lactose intolerant as adults, but nearly everyone produces sufficient lactase as an infant. however, in some cases, genetic mutations can occur that make an infant lactose intolerant. from an evolutionary perspective -- over thousands of years -- why would lactose intolerance in infants be very rare in the population?

Answer 1

It is because infants with lactose intolerance usually die in early stages, so they never have the chance to transfer the mutation on to their offspring.

Step-by-step explanation:

Lactose intolerance is an disorder, characterized by inability to digest lactose sugar. It is caused by a mutation that leads to insufficient production of lactase enzyme that digest lactose.

Lactose intolerance is rare in population, because affected infants have very less chances of survival. Infants depend on breast milk and due to lactose intolerance, they cannot digest milk as lactose is a main carbohydrate in milk. Thus, affected infants get died in early life stages and never get chances to pass the mutated genes to their progeny.

Answer 2

Lactose intolerance in infants is very rare in the population.

This is because lactose intolerant in infants cannot digest breast milk and therefore it dies.
They don't have a chance to pass the mutation on to their children.

Lactose is found in dairy items like yogurt and drain. In today's life, lactose intolerance in infants is more common in the population because today there are alternatives to breast milk.
For example, Soy milk, and lactose-free formula. Therefore lactose intolerant in infants can survive.