 Because the environmental conditions that would facilitate each transition are heavily overlapping, the scientists surmise, a common switch could have evolved for the two transitions.The main problem with this idea is the timing at which the transition is presumed to have happened, and how this would then translate into the genetic predisposition to type 2 diabetes and obesity.For example, the decline in reproductive investment in human societies (the so-called r to K shift) has occurred far too recently to have been caused by a change in genetics.