B

It may be pointed out that warfare（战争）as practiced by man has no parallel in nature. This is to say that within the more highly developed animal populations of this earth, there is not now, nor has there been similar destruction within a species（物种）itself. In fact, one has to go to the lowliest forms of animal life, such as certain kinds of ants, to find anything comparable to human warfare. It is a curious fact that mankind appears to give the killing of his own kind a good reason by imaging that it is a "law of nature". There are now a lot of wrong ideas about the laws of nature, of which this is one of the most incorrect and fateful（致命的）. Political beliefs have been based upon it with results that have come near to destroying human civilization. The theory that war is a biological necessity, that it is nature's method of controlling population and believing in the survival（生存）of the strong and the elimination（灭亡）of the weak, is totally wrong and insupportable. Within the last century, when wars have been common all over the world, the human population of the earth has almost doubled.

The main idea of this passage is_____.