CREATION BY EVOLUTION
do change in this way. Just such an objection might be raised by one who paid a short visit to this planet and was assured that children became men and women. “I have been here for a whole week,” the visitor might well say, “and I have looked everywhere for this transformation, but I have never seen a child turn into a man or woman.” But a week is a far greater part of the period of human growth than is the time of human observation in the life of a species. Furthermore, if the visitor prolonged his stay indefinitely he would still never see a child “turn into” a man or woman, for between the two intervenes a growth so gradual that no difference is perceptible from day to day or from week to week. So is it with evolution. One species does not “turn into” another: it becomes another species through a series of gradual changes, and at no time would it be possible to say—“Now the change has come; what was species A yesterday is species B to-day.”
To prove that species A, known to us only from remains in the rocks, had become species B of to-day it would be necessary to restore to life the animals of innumerable past generations of beings and to show that, whereas those of adjacent strata could interbreed, their ancestors (species A) could not interbreed and produce fertile offspring with their living successors (species B). As this is manifestly impossible, we infer from the gradual changes of form or structure preserved in the rocks that A is a different species from B, which has apparently sprung from A by direct descent.
If, however, we cannot witness the transformation of one species into another any more than we can witness the sudden transformation of a child into a man or woman, we are able to witness the results of a series of changes in living forms in adaptation to the conditions of life—
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