While it is often said that love makes the world go round, scientist take a less (浪漫的) view. To their minds, energy is the (根本的) force at work. All animal life is dependent on obtaining sufficient energy from food. Deer, like other wild animals, do this through eating as much food as possible in the summer, when food resources are (充足的) . any (超额量) of energy over their needs is (储存) in the body in the form of fat. Then when food becomes (不足的) in the winter, they can live off the fat. In addition, nature helps them to survive the winter by offerring (防卫措施) of slowing down their metabolism. However, when the winter is particulary long, deer may have to(取出) the fat they have built up. under such conditions, only deer in good condition are able to(存活) and (产仔) new fawns.