Many people feel that human beings are responsible for the disappearance of some other animal species. While we may have hastened the disappearance of some, abundant evidence suggests mankind has had little impact. Biologists point out that 50 species can be expected to disappear in the twentieth century but also remind us that about 50 species can be expected in the nineteenth century, and 50 species in each of the centuries before that. Dr. T. H. Jukes at the University of California has pointed out that about 100 million animal species have become extinct since life began on Earth about 3 billion years ago. Thus, animals come and animals go as a natural consequence of something Mr. Darwin discovered. The human race is a recent newcomer to the scene, so we've had nothing whatsoever to do with the disappearance of millions of species. In fact, when it comes right down to it, we're a miserable failure at genocide(种族灭绝 ). In spite of an all-out centuries-old war on rats, we haven't made a dent in their numbers, much less extinguished a single species. And in spite of all our high technology we haven't been successful in eliminating a single undesirable insect species! A friend of mine owns most of the Douglas DC-7 aircrafts left in the world. They make excellent spray planes because they can carry a lot of insecticide and fly for a very long time over great distances. Last year, his company sprayed most of the western Sahara and the Sahel regions of Africa to hold down the locusts and grasshoppers. This year, the environmentalists put pressure on the UN to stop it because dieldrin and malathion might cause an increase in the cancer risk of people in the western Sahara and the Sahel. As a result, the hoppers and locusts are back by the zillions and the crops are failing. But the people of West Africa certainly aren't going to worry about dying of cancer they are dying of starvation instead. I've come to the conclusion that the people who are trying to save the world are probably quite sincere about it but they don't know much about science and certainly nothing about systems engineering. According to the author, which of the following evidence proves that human beings aren't responsible for the disappearance of some other animal species?