When times are tough, that prehistoric urge to splurge on high-calorie treats like M&Ms still kicks in. Daniel M.N. Turner/NPR hide caption toggle caption Daniel M.N. Turner/NPR The Salt Pig Out In The Winter Or When Money's Tight? Blame Evolution February 1, 2013 Why do we reach for that handful of M&Ms and other high-calorie treats under stress? In prehistoric times, such gluttony was probably a useful response to scarcity. That "feast before famine" instinct is less helpful in modern times, when obesity is a bigger health risk than starvation – but evolution hasn't had a chance to catch up.