Homo sapiens is not a finished product. In fact, there is evidence that modern humans are evolving faster than ever before, as mutations and natural selection continue to change us. How so? For one thing, we drink milk.
Read about the other changes in humans over time at mental_floss. Link
(Image credit: Flickr user Lucas Leite)
Historically, the gene that regulated a human’s ability to digest lactose shut down as they were weaned off of their mother’s breast milk. But when we began domesticating cows, sheep and goats, being able to drink milk became a nutritionally advantageous quality, and people with the genetic mutation that allowed them to digest lactose were better able to propagate their genes.
A 2006 study suggests this tolerance for lactose was still developing as early as 3,000 years ago in East Africa. That genetic mutation for digesting milk is now carried by more than 95 percent of Northern European descendants.
Read about the other changes in humans over time at mental_floss. Link
(Image credit: Flickr user Lucas Leite)
Also, it doesn't happen in individuals, so feeding your cat milk is only going to give it diarrhea.