Lactose intolerance occurs when the enzyme, lactase, that digests lactose is not produced after infancy in humans. The incidence of lactose intolerance varies in different racial groups. The graph shows the distribution of lactose intolerance in different human populations.

Lactose intolerance occurs when the enzyme, lactase, that digests lactose is not produced after infancy in humans. The incidence of lactose intolerance varies in different racial groups. The graph shows the distribution of lactose intolerance in different human populations.

What can be hypothesized from the graph?