Milk: It Does a Population Good
For nearly all of human history -- heck, for nearly all the history of a lineage that started 85 million years ago with this shrew-like furball and ended with us -- milk was consumed in infancy. The genetic processes involved in breaking down lactase, milk's main sugar, shut down when babies finished weaning.
Then, about 9,000 years ago, cattle were domesticated for the first time, offering great advantage to anyone who could take sustenance from their milk. Lactose-processing mutations spread fast and wide, first in north-central Europe and later in Africa. The majority of humankind is now lactose-tolerant, making these mutations among the fastest-spreading in known human history.
Image: bluewaikiki/Flickr