That lactose tolerance has evolved independently four times is an instance of convergent evolution.

Natural selection has used the different mutations available in European and East African populations to make each develop lactose tolerance.

Mutations in these regions are associated with lactose tolerance into adult life.

They developed lactose tolerance, the unusual ability to digest lactose in adulthood.

In most mammals, the gene for lactose tolerance switches off once an animal matures beyond the weaning years.

The genes of adult lactose tolerance have evolved independently in various ethnic groups.

Eating yogurt with live bacterial cultures seems to improve lactose tolerance in children and adults who cannot absorb lactose.

Another locus of lactose tolerance is in Northern India.

The appearance of lactose tolerance in human populations with a long tradition of raising domesticated animals for milk production has been suggested as another example.

One of the genes, which arose among Europe's first cattle herders 5,000 years ago, enables people to drink milk in adulthood, an ability known as lactose tolerance.