278 THE MEANING OF EVOLUTION 
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 
