Dairy Cattle Were Unknown in Thai Culture Until Recently, and 97

Multiple Choice

Dairy cattle were unknown in Thai culture until recently, and 97 percent of Thai people are lactose intolerant as adults. Which explanation for such widespread lactose intolerance is most likely correct?

A) Allergies are becoming more common in humans as more chemicals are being encountered during longer lifetimes.
B) Evolutionarily, producing an enzyme to break down a sugar that will never be encountered is wasteful.
C) The ability to digest sugar in milk is determined by environment, and most humans are not exposed to milk as a food source beyond childhood years.
D) There is no good explanation for this situation in humans.