Take one of the most striking, if not the most crucial difficulties, one which puzzled and perplexed Darwin from the first and was made a fruitful text for criticism by his adversaries, the development of the eye. Was it to be supposed that so delicate, so complex, and so highly adapted an organ could be produced by mere accidental variation working through inheritance and the gradual survival of the fittest? And Darwin investigated and compared and reflected, until he was ready to state his position thus: ‘Reason tells me, that if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further the eye ever varies and the variations be inherited, as is likewise certainly the case; and if such variations should be useful to any animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, should not be considered subversive of the theory.’[284] Sometimes the difficulties appear in themselves insignificant, yet their bearing is such as to make them of extreme importance. For example, how the useful institution of neuter insects could be developed by inheritance was a terrible problem. It ‘at first appeared to me insuperable, and actually fatal to the whole theory.’[285] Study and observation wear it away; yet it is disposed of with the candid remark: ‘I must confess, that, with all my faith in natural selection, I should never have anticipated that this principle could have been efficient in so high a degree, had not the case of these neuter insects led me to this conclusion.’[286] Or there is the coloring of the peacock’s tail, which has to be explained by extreme wrestlings of logical ingenuity. And again, as compared with these seemingly petty obstacles, there are the great questions involved in the essential tissue of the theory itself. There are the gaps, the breaks, the missing links, not only between man and his simian ancestors, but completing all the gradations between all the existing forms of development. Many and many an hour, and one may say, many a year of anxious thought did Darwin bestow on this point. He could meet it only with such eager comment as he makes after his prolonged study of the orchids: ‘In the comparatively few orchids described in this volume, so many and such plainly-marked gradations in the structure of the rostellum have been described, ... that we may well believe, if we could see every orchid which has ever existed throughout the world, we should find all the gaps in the existing chain, and every gap in many lost chains, filled up by a series of easy transitions.’[287] And there were such vast problems as sexual selection and pangenesis, which we discussed in a previous chapter, and there was even the central element of