embryo had been divinely arranged, it would surely have gone along lines of direct growth from the germ to the finished form: would not have displayed various metamorphoses having no relations either to passing needs or to ultimate structure and mode of life. With which evidence may be joined the evidence furnished by rudimentary organs, which are full of meaning on the evolution hypothesis, but worse than meaningless in the special-creation hypothesis.
But these four great groups of facts, suggesting in different ways the same history, stand thus far without assigned cause. How come these progressive modifications to have taken place? and why are the modified forms connected with one another in the ways shown alike by paleontology, by classification, by distribution, and by embryology? The reply is that we need only look around to see everywhere at work a general cause which, if it has been at work throughout all time, yields an explanation. Take any plant or animal and expose it to a new set of circumstances (circumstances not so unlike its previous ones as to prove fatal), and it begins to change; and the change is one which eventually adapts it to the new conditions. By what special causes the adaptive modifications are effected does not at present concern us. Here the argument requires us only to recognize the truth that in some way the organization is molded to the new conditions. Though—to illustrations furnished by cultivated plants and domesticated animals—it may be objected that artificial selection has been at work, yet, since artificial selection implies variations, it implies that the selected plants and animals have been modified by external influences, and that the modifications have been inherited and accumulated. And then, if there needs a case in which artificial selection has not come into play, we have a sufficiently striking one in the human race itself. Unless there be adopted the hypothesis (excluded by Lord Salisbury's implied belief) that varieties of men have been independently created, the conclusion is irresistible that their differences have been caused by unlikenesses in their lives carried on in unlike environments. Either their differences are uncaused, which is absurd, or they are differences which have unfitted each variety for its conditions, which is also absurd, or they are differences which have fitted each variety for its conditions; and, if so, they have resulted from the response of the constitution to the conditions themselves: the only supposition which is not absurd. And that this is the necessary interpretation is shown by cases in which—either by the killing off of unfit individuals, or by the effects of habit, or by both—extraordinary adaptations have been produced. There are, as examples, the Fuegians, who in their wretched islands go about naked while the falling snow melts on
