However, this implies that the period after which humans migrated out of Africa would have provided sufficient time to reverse any pre-existing famine-adapted alleles, for which there is little to no evidence. One criticism of the 'thrifty gene' idea is that it predicts that modern hunter gatherers should get fat in the periods between famines.
The idea that humans migrated out of Africa after a famine period and that any pre-existing famine-adapted genes would have been reversed by then, is challenged by the lack of evidence for such alleles. The 'thrifty gene' theory is criticized because it predicts modern hunter-gatherers should gain weight during periods without food.