[Sometimes something is so good it must be reposted – RAS]
“Science is weak about these prehistoric things in a way that has hardly been noticed. The science whose modern marvels we all admire succeeds by incessantly adding to its data. In all practical inventions, in most natural discoveries, it can always increase evidence by experiment. But it cannot experiment in making men; or even in watching to see what the first men make.
But he cannot watch the Missing Link evolving in his own backyard. If he has made a mistake in his calculations, the airplane will correct it by crashing to the ground. But if he has made a mistake about the arboreal habitat of his ancestor, he cannot see his arboreal ancestor falling off the tree. He cannot keep a caveman like a cat in the backyard and watch him to see whether he does really practice cannibalism or carry off his mate on the principles of marriage by capture. He cannot keep a tribe of primitive men like a pack of hounds and notice how far they are influenced by the herd instinct.
If he sees a particular bird behave in a particular way, he can get other birds and see if they behave in that way; but if be finds a skull, or the scrap of a skull in the hollow of a hill, he cannot multiply it into a vision of the valley of dry bones. In dealing with a past that has almost entirely perished he can only go by evidence and not by experiment. And there is hardly enough evidence to be even evidential. Thus while most science moves in a sort of curve, being constantly corrected by new evidence, this science flies off into space in a straight line uncorrected by anything.”
- G. K. Chesterton, The Everlasting Man