出生于本世纪初的英国动物学家查理·艾尔顿，从牛津大学生物系毕业后，作为一家公司的顾问，有一次到北极地区去进行动物生态考察。到达北极地区后，一天，他随手翻看这家公司历年来向爱斯基摩人收购毛皮的账簿。他无意中发现，公司收购的北极狐的毛皮，总是每四年就会出现一 Born in the beginning of this century, the British zoologist Charlie Elton, once from the Department of Biology, Oxford University, as a company consultant once went to the Arctic for ecological zoology. One day after arriving in the Arctic, he glanced at the company's books of fur purchases from Eskimos over the years. He inadvertently found that the fossil Arctic fox acquired by the company always appears one every four years