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Similarly with the first two objections. If the degree of adaptation has not increased during evolution, then it is clear that progress does not consist in increase in adaptation. But it does not follow that progress does not exist; it may quite well consist in an increase of other qualities. So with complexity. Complexity has increased, but increase in complexity is not progress, say the objectors. Granted: but may there not be something else which has increased besides mere complexity?

No; the remedy for all our difficulties, and indeed the only way in which we can arrive at the possibility of saying whether biological progress exists or no, is to adopt the positive method.

Let us then begin our survey of biological evolution in the endeavour to find whether or no progress is visible there. To start with, we must be clear what are the sources of our knowledge on the subject.

Direct observation of progressive evolution has, of course, not yet been possible in the period—biologically negligible—in which man has directed his attention to the problem; and historical record is also absent. The best available evidence is that of paleontology: here the relative positions of the layers of the earth’s crust enable us to deduce their temporal sequence—and naturally, that of the organisms whose fossil remains they embalm—with a great deal of accuracy.ssss1