CAN WE SEE EVOLUTION OCCURRING?
the naked ones, are designated by other names. One called Diffiugia corona (Fig. 1) was selected for observation and breeding. It is a miscroscopic creature about 1–150th of an inch in diameter.
These creatures multiply for long periods without any sexual process; that is, each individual divides into halves, and each half then develops into a complete cell, which is later in turn subjected to the same dividing process. Any individual is therefore the offspring of but a single parent; not of two parents, as in the higher animals. The method of reproduction in Difflugia is shown in Figure 2. A new generation is produced about every two to four days, so that in the course of a year or two many generations may be followed through thousands of descendants produced from one individual.
Do these thousands of descendants all remain hereditarily alike? Or do they gradually and slowly diverge, becoming hereditarily different, as the doctrine of evolution sets forth?
This was studied by allowing a single individual to reproduce for many generations, until it had produced thousands of offspring. In the early generations of such an experiment, hereditary changes cannot be detected. The offspring often differ from the parents in certain respects, but most of these differences appear not to be inherited. The next generation shows similar differences, but as the generations increase in number we find that certain diversities accumulate and become hereditary. In some descendants the spines become longer; in others they remain shorter. In some the bodies are larger; in others they are smaller. Different combinations of size of bodies and of length of spine appear. These differences are inherited. In time from the original single individual a number of diverse stocks have
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