The bulky-browed primates, the scientists speculate, were unable to adapt their hunting skills to small game. And that was not a small thing, because big game are just that: big. Hunting larger animals — chasing them, felling them, hauling them home — expends considerable resources of time and energy. Small game, on the other hand, is less demanding of hunters. It might take more cunning to catch a rabbit, but it generally takes less physical energy. And this discrepancy might have made an important evolutionary difference, the thinking goes, particularly as large animals reduced in numbers."