个头太大并不见得是好事。科学家最近对北美犬化石的一项研究表明，在进化过程中，狗的个头越长越大，随之猎捕的食物也越来越大，结果却使其更加迅速地灭绝。此前，就有科学家对食肉动物进行过调查，发现体重大于21.5公斤的食肉动物的“食谱”往往受到限制。体重较小的食肉动 Being too big is not necessarily a good thing. A recent study by scientists on fossils from the North American dog shows that during the course of evolution, the longer the dogs became, the larger the food they hunted and the more quickly they became extinct. Previously, scientists surveyed carnivores and found that the “recipes” of carnivores weighing more than 21.5 kilograms are often restricted. Smaller-weight carnivores