Page:The British Warblers A History with Problems of Their Lives - 7 of 9.djvu/32

 movements visible to an external observer may be absent in slight, and sometimes in intense emotions. May not this be true of the emotion of a bird, and may not the relation between the strength of the emotion and the intensity of the expressional movement, which is here assumed, be open to question? Circumstances at least seem to show that such may be the case. For do we not observe in bird life numberless degrees of emotional reaction, ranging from almost imperceptible movements up to extravagant actions, corresponding to a sexual instinct the strength of which cannot well be differentiated in x y z and all the rest.

The proposition, as I understand it, is somewhat as follows: Not all the males are of equal strength; the stronger individuals are capable of greater sexual emotion. This emotion must somehow express itself, and does so in many cases by what are known as motor reactions. These reactions excite the female. The stronger the male the stronger the reaction and the greater chance that male will have of overcoming the reluctance of the female, pairing, and transmitting its greater strength to descendants, and the greater scope will there be for the development of secondary sexual characters, which will naturally result from greater strength and possibly contribute to a more effective pairing situation. And at first sight this would appear to be a reasonable interpretation of all the peculiar attitudes, antics, and vocal extravagances which are the subject of our investigation; but when we attempt to bring it into accord with the phenomena which we actually observe, the task is not altogether an easy one. Certain essential features of the theory are not very clear to me; for instance, there is no very definite expression of opinion as to whether the theory is one to explain the evolution of antics from movements that at some earlier period were not so pronounced, by the selection of variations all tending in the direction of greater activity; or whether it only claims to show how, having once arisen, they may now have a meaning in relation to something in the