It is a fundamental principle of science that man has no answer to any problem until, through observation and experiment, he is able to find it out. He must work from individual details, an adequate number of which will enable him to frame a more or less complete generalization. Such result, however, is not necessarily final because every inductive solution reveals new problems. Other factors, not originally discerned, may confuse conclusions or a farther cause must in turn be explored. For example, we have worked out in detail the proximate origin of tens of thousands of species of animals and plants, but we cannot minutely trace pedigrees through geologic ages. Here ancestral records are lost in the “infinite azure of the past,” to be sought only by the torchlight of palaeontology. Furthermore we can rarely affirm one single cause or group of causes as covering the whole range of the phenomena studied.