CAN WE SEE EVOLUTION OCCURRING?
the circle; yet men have discovered this fact and have measured the present rate of the motion. The fixed stars are not in fact fixed in their relation to one another; slight changes of position occur, some of them requiring centuries for detection; yet men have detected them. Certain radioactive substances disintegrate so slowly that it requires millions of years for a given portion to transform, yet the changes have been detected and their rate has been measured. If we can detect these things why should we not be able to detect—to catch in progress—the changes that we call evolution? We cannot directly see the growth of a tree, but by taking photographs at intervals and running them through a moving picture machine we can see the tree grow, and we can determine how its growth occurs. Ought we not to be able to get some sort of a moving picture of evolutionary change?
The task is bound to be difficult. The process of evolution is complex. Evolutionary changes move in many different directions. Some organisms degenerate; others grow more complex and become adapted to more varied conditions; still others change hardly at all. The process cannot be uniform; it produces diversity, not simplicity. What sort of changes should we expect to find if we could watch certain organisms closely enough to see the evolutionary changes that occur in them during a human lifetime?
We should have to study some organism that produces many generations while man passes through but one. Fortunately, there are many such organisms—creatures that produce a new generation every day or every few days. We should have to begin with a single individual and follow its offspring for many generations, obtaining great numbers of descendants. According to the theory of evolution, slight changes would occur as the generations pass. These changes
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