Lactose tolerance

I always wondered why I was seeing so many lactose intolerant people.. it seemed natural to me that humans should be able to drink milk. The thought of it being a mutation definitely crossed my mind. 

Looks like I was asking the wrong question! http://www.slate.com/articles/health_and_science/human_evolution/2012/10/evolution_of_lactose_tolerance_why_do_humans_keep_drinking_milk.single.html