World-power and evolution / by Ellsworth Huntington.

  • Ellsworth Huntington
Date:
1919
Catalogue details

Licence: In copyright

Credit: World-power and evolution / by Ellsworth Huntington. Source: Wellcome Collection.

    117/296 page 113
    For our present purpose another change is far more important. At this time apparently there occurred one of the most vital steps in the evolution of our direct ancestors, the mammals. Extreme aridity and low temperature were both characteristic of certain epochs of the Permian Period. Among the more progressive types of land animals aridity has a tendency to accelerate development. It places a premium upon the power to travel, and especially upon speed. As Lull puts it: “Not only are food and water scarce and far between, but the strife between pursuer and pursued becomes intensified—neither can afford to be out-distanced by the other. This means increased metabolism, which in turn generally implies not only greater motive powers but higher temperature. With increasing cold a premium would be placed upon such crea¬ tures as could maintain their activity beyond the limits of short¬ ening summers, and this could be accomplished only by the development of some mechanism whereby a relatively constant temperature could be maintained within the animal regardless of external conditions.” In other words, there arose warm-blooded animals whose temperature was more or less independent of the surrounding air instead of varying with it as is the case in cold¬ blooded animals. Among mammals this led to the production of the young within the body of the mother instead of from eggs in which the mother took little or no interest after they were laid. Among birds it forced the mother to care for the eggs if they were to be hatched. Thus the relation of mother and child became firmly established. The later development of this relation has been the chief source of all that is best in mankind. We must not suppose that during the climatic stress of the Permian the mammals emerged full-fledged. The first warm¬ blooded creatures were not warm in the sense that we are. Their temperature varied through wide limits, just as now is still true of infants even when they are perfectly healthy. Nor were the young born alive at first, for eggs continued to be laid as is today the case with some of the most primitive mammals of
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