All adult mammals but humans are lactose intolerant. Follow human geneticist Spencer Wells, director of the Genographic Project of the National Geographic Society, as he tracks down the genetic and societal changes associated with the ability to digest lactose as adults—or lactose tolerance.

Explore how evolutionary biology and cultural changes led to the evolution of lactose tolerance in this educational video.

Free teaching resources supporting this short film can be found at http://www.hhmi.org/biointeractive/ma...