Among students of animals and plants there is no longer any question as to the truth of evolution. That the animals of the present are the altered animals of the past, that the plants of to-day are the modified plants of yesterday, that civilized man of to-day is the savage of yesterday and the tree-dweller of the day before, is no longer debatable to the great mass of biologists. To older men hampered by the convictions of an earlier age this dictum of modern science may still be a little uncertain. The working biologists of the world have no doubt. They differ radically as to what brought about this change, they dispute vigorously as to the rate of change, but as to the fact of the change there is no difference of opinion. Under these conditions the thinking man is out of joint with the times when he sets himself against the idea of evolution. He may be so immersed in other lines as to be indifferent to the problem; but when he is hostile to it, he marks himself as clearly against his day. Many have been against their day and have been right. Very great men have often been against the opinions of their times and have come to be leaders of the world's later thought. But ordinary men in ordinary times who think differently on a special subject from the specialists of the times are not very likely to be right. It is safe for most of us to accept as true an opinion on which specialists on that subject agree. It seems clear to me then that the thinking man to-day has in the matter of evolution a double duty. He must become reasonably acquainted with the theory that so largely affects all present knowledge, and he must wrestle with the theory until it no longer hinders the hold of religion upon his life. He may be perfectly sure that he does not clearly understand both, but he must get them into reasonable concordance before he can be quite at peace. Truth is true no matter how it is acquired. There can be no doubt as to the essential truth of religion: its fruits proclaim its worth. There can be no doubt as to the essential truth of evolution; the clarity it has brought into the sciences is the evidence of the value of the conception. That it will persist in its present form, that it will be unchanged by later additions to our knowledge is of course unthinkable. It may be incomplete, it may be undeveloped, but so far as it goes it contains the truth. Under these conditions, how can we bring peace into our own mind? These two important provinces seem so often to be at variance. The difficulty may lie in one of two places. In the first place, each truth may be stated in terms so peculiar to its own subject as to convey no meaning to the student of the other branch. There is a second, and more harassing possibility. The same words may be used by students in each branch but each side may put a different significance into the terms. Then each believes he understands the other, when he really does not.