Lactose intolerance
This is an old revision of this page, as edited by Sterile (talk | contribs) at 00:58, April 23, 2007. It may differ significantly from current revision.
Lactose intolerance is a condition where individuals cannot digest lactose, a sugar found in milk. When a lactose intolerant individual injests of milk, he or she will get a stomachache. Other symptons include cramps and bloating. Such individuals do not produce an enzyme called lactase that breaks down lactose after weaning.
The proportion of lactose intolerant individuals varies by region on the planet. 99% of Chinese are lactose intolerant, whereas only 10% of Americans are. Recent research indicates that lactose intolerance is high where cows were not domesticated. This caused a gene to be permanently switched on, and natural selection favored a continued production of lactase during adulthood.