CREATION BY EVOLUTION
of experience and tradition that is cumulative from generation to generation. At each of these levels some types of living beings have specialized and remain fixed to this day in their one-sided efficiency, or else they have been extinguished by more progressive types; others have remained generalized, and some of these have given birth to the progressive types which constitute the next upward step.
After this brief survey, it remains to ask whether the balanced advance we have been discussing can properly be called progress, in the usual sense of that term, or whether we have not been misleading ourselves by using a term which implies real improvement in what to us is valuable, when we should have really called it mere directive change.
When we come to consider the main steps in biological advance that are enumerated above, we find that it is possible to sum them up under a few heads. There has been on the whole a considerable increase in size; there has been improvement in the organs adapted to carrying out each type of function taken separately-organs of digestion, of locomotion, of protection, of support, of sense-perception, of reproduction; there has been improvement in the relation between these organs-that is, in the way in which the different parts of the body and their functions are correlated and coördinated; there has been improvement in the control exercised by the brain over the body as a whole, and in the quality and extent of the information received about the outside world by which this control is achieved; there has been improvement in the self-regulating capacity of the body, as is witnessed by constant temperature or constant chemical composition of blood in higher forms; there has been a decreasing reproductive waste, an increasing care for young; there has been an increase in mutual aid between individuals; there has been an increase of emotional
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