Note 73 — Chapter V

"Biology," i, p. 351. I am not quite sure that I understand what Mr. Spencer means by "direct" proof. In the passage immediately following the sentence last quoted, he speaks of "the kind and quantity of direct evidence that all organic beings have gradually arisen," etc., whereas, in a previous passage, he had admitted that the facts at present assignable in direct proof of this hypothesis are insufficient. I presume he meant insufficient in number. (Compare "Biology," i, pp. 351 and 352). Now, I should say that direct proof of the hypothesis that all animal organisms have arisen successively out of one another would require more or less positive evidence of such occurrences; and that the proof which is afforded by what has taken place within the limits of a single species in the course of successive generations would be indirect evidence of what may have taken place in the evolution of different species, because it requires the aid of analogy to connect the two. I am not aware that there is supposed to be any proof of the evolution of species out of species, excepting that which is derived from what has taken place in single races in the development of the ovum into the infant, the development of the infant into the mature animal, and the limited varieties of structure appearing among individuals of the same race. As I go on through the examination of Mr. Spencer's argument, it will appear whether there are grounds for regarding this kind of reasoning as satisfactory or the reverse.