It is certainly surprising to find Darwin ascribing even this difference in size between the sexes to the action of selection. Is it not a little ludicrous to suppose that the females have reduced the males to a size too small for them to catch? There are many cases known in the animal kingdom where there is a difference in size between the two sexes, especially in the group of insects; but I doubt very much if they are to be accounted for as the result of sexual selection. In some of these cases Darwin accounts for the larger size of the female, on account of the large number of eggs which she has to carry. In other insects where the male is larger, as in the stag-beetle, the size is ascribed to the conflicts of the males, leading to the survival of the larger individuals. In still other cases, where the males are larger, but do not fight, an explanation is admittedly wanting; but it is suggested that here there would be no necessity for the males to be smaller than the females in order to mature before them (as is supposed to happen in other species), for in these cases the individuals are not short-lived, and there would be ample time for pairing. Again, although the males of nearly all bees are smaller than the females, yet the reverse is true in those forms in which the females are fertilized during the marriage flight. The explanation offered is that in these forms the male carries the female, and this is assumed to require greater size on his part. This loose way of guessing, as to a possible explanation, is characteristic of the whole hypothesis of sexual selection. First one, and then another, guess is made as to the causes of the differences between the sexes. It is not shown in a single one of the instances that the postulated cause has really had anything to do with the differences in question; and the attempt to show that the theory is probable, by pointing out the large number of cases which it appears to account for, is weakened to a very great degree by the number of exceptional cases, for which an equally ready explanation of a different kind is forthcoming. This way of giving loose rein to the imagination has been the bane of the method that has followed hard on the track of Darwin’s hypothesis, and for which his example has been in no small measure responsible. Thus, in the case just quoted, there are no less than four distinct conjectures made to account for the differences in size between the sexes, and each guess involves an entirely different set of processes. Considering the complicated relation of the life of organisms, it may be doubted if any of the imagined processes could bring about the result, and certainly not a single one has been shown to be a real, or a sufficient, cause in the evolutionary process. Neither the actuality of the postulated causes, nor their application to a particular case, has been shown to exist.