"... The male emperor penguin brooding his mate's egg over the Antarctic winter cannot be relieved by his mate because the growth of the ice shelf puts the sea and food beyond reach. So, in the interests of producing an offspring, he fasts for months—a feat any human would find impossible. Other potential solutions to this problem, such as shorter stints of breeding and trekking repeatedly across the ice shelf during the winter, presumably proved to be less successful. The penguins that fasted all winter were the ones whose ancestors had best survived with this adaptation. Examples like this emphasise how dependent is the organisation of behaviour on the ecology of the species. Differences between individuals in the processes of development are to be expected."