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Show 262 THE PRINCIPLES OF PART II. strongest, aud with some species the best armed, chive away the weaker males; and the former wo~ld then unite with the more vigorous and best-nouns~1ed females as these are the first to breed. Such VIgorous. pairs 'would surely rear a larger number of offspring than the retarded females, which would be compell:d, supposing the sexes to be numerically equal, to umt_e with the conquered and less powerful males ; and t~ns is all that is wanted to add, in the course of successrve generations, to the size, strength and courage of the males, or to improve their weapons. . But in a multitude of cases the males whwh conquer other males do not obtain possession of the females, independently of choice on the part of t_he latter. The courtship of animals is by no means so simple and short an affair as might be thought. The females are most excited by, or prefer pairing with, the more ornamented males, or those which are the best songsters, or play the best antics; but it is obviously probable, as has been actually observed in some cases, that they would at the same time prefer the more vigorous and lively males.4 Thus the more vigorous females, which are the first to breed, will have the choice of many males; and though they may not nlways select the strongest or best armed,. they will select those which are vigorous and well armed, and in other respects the most attractive. Such early pairs would have the same advantage in rearing offspring on the female side as above explained, and nearly the same advantage on the male side. And this apparently has sufficed during a long course of generations to add not only to the strength and fighting-powers of 4 I have received information, hereafter to be given, to this effect with respect to poultry. Even with birds, such as pigeons, which pair for life, the female, as I hear from M:r. Jenner Weir, will desert her mate if he is injured or grows weak. CJJAP. VIII. SEXUAL SELECTION. 2G3 the males, but likewise to their various ornaments or other attractions. In the converse and much rarer case of the males selecting particular females, it is plain that those which were the most vigorous and had conquered others, would have the frees~ choice ; and it is almost certain that they w~uld select v1gorous as well as attractive females. Such pairs would have an advantage in rearing offspring more especially if the male had the power to defe~d the female during the pairing-season, as occurs with some of the h~~her animal~, ?r aided in providing for the young. I he same prmc1ples would apply if both sexes mutually preferred and selected certain individuals of the opposite sex;. supposing that they selected not only ~he. ~ore attractive, but likewise the more vigorous mdividuals. Num,erical Proportion of the Two Sexes.-! haYe rem_arl~ed that sexual selection would be a simple affair. If the males considerably exceeded in number the females. Hence I was led to investigate, as far as I could, ~he proportions between the two sexes of as many ammals as possible ; but the materials are scanty. I will here give only a brief abstract of the resu~ts, retaining the details for a supplementary discussiOn, so as not to interfere with the course of my argumen~. Domesticated animals alone afford the opp~rtumty of ascertaining the proportional numbers at _birth; but no records have been specially kept for this purpose. By indirect means, however I have col~ecte~ a considerable body of statistical d~ta, from wh.ICh It appears that with most of our domestic ammals the sexes are nearly equal at birth. Thus with race-horses, 25,560 births have been recorded durin()' twenty-o~e years, and the male births have been to th~ female births as 99·7 to 100. With greyhounds the |