Difficult though it may be to follow the sequence of forms which have endlessly succeeded and replaced one another on the face of the earth, since the beginning of the world, it is certain that all living creatures are closely related; and the magnificent and fertile hypothesis of evolution, which seeks to explain how extant forms are derived from extinct, has the immense advantage of giving a plausible reason for the majority of the facts which at least cease to be completely unintelligible. Otherwise we can certainly never imagine how so many instincts, and these so complex and perfect, could have issued suddenly "from the urn of hazard." But Fabre will suppose nothing; he will only record the facts. Instead of wandering in the region of probabilities, he prefers to confine himself to the reality, and for the rest to reply simply that "we do not know." This stern, positive, rigorous, independent, and observant mind, nourished upon geometry and the exact sciences, which has never been able to content itself with approximations and probabilities, could but distrust the seductions of hypotheses. His robust common sense, which was always his protection against precipitate conclusions, too clearly comprehends the limits of science and the necessity of accumulating facts "upon the thorny path of observation and experiment" to indulge in generalization. He feels that life has secrets which our minds are powerless to probe, and that "human knowledge will be erased from the archives of the world before we know the last word concerning the smallest fly." This is why he was regarded as "suspect" by the company of official scientists, to whom he was a dissenter, almost a traitor, especially at a moment when the theories of evolution, then in the first flush of their novelty, were everywhere the cause of a general elation. No one as yet was capable of divining the man of the future in this modest thinker who would not accept the word of the masters interested, but in opposing the theory of transformation, far from being reactionary, Fabre revealed himself, at least in the domain of animal psychology, as an innovator, a true precursor. Moreover, his observations, always so direct and personal, often revealed the contrary of what was asserted or foreseen by the magic formulae suggested by the mind. To the ingenious mechanism invented by the transformists he preferred to oppose, not contrary argument, but the naked undeniable fact, the obvious testimony, the certain and irrefragable example. "Is it," he would ask them, "to repulse their enemies that certain caterpillars smear themselves with a corrosive product? But the larva of the Calosoma sycophanta, which feeds on the Processional caterpillar of the oak-tree, pays no heed to it, neither does the Dermestes, which feeds on the entrails of the Processional caterpillar of the pine-tree."