Some biological functions, like lactose intolerance, are designed to force us to age & evolve.

Some biological functions, like lactose intolerance, are designed to force us to age & evolve. But sometimes animals stop aging but somehow start reproducing & a new species is born (see: lots of lizard & dog breeds). But! Scientists have discovered that injecting iodine into these species forces them to age, turning them into the OTHER species! Evolution's weird!
http://io9.com/5826750/scientists-show-that-peter-pan-grows-up-with-a-shot-of-iodine