Human evolution

Biology may be the science that I am least interested in, but I found this story from the Times the other day quite interesting. It turns out that humans developed the ability to digest milk in adulthood incredibly recently, like thre thousand years ago. Also, we can tell that this trait was evolved in response to the cultural practice of keeping domestic cattle and using their milk for food.

Throughout most of human history, the ability to digest lactose, the principal sugar of milk, has been switched off after weaning because the lactase enzyme that breaks the sugar apart is no longer needed. But when cattle were first domesticated 9,000 years ago and people later started to consume their milk as well as their meat, natural selection would have favored anyone with a mutation that kept the lactase gene switched on.

You have to wonder, though, don't you: why wasn't this trait intelligently designed by our all-knowing, infinitely benevolent creator?