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Show 316 THE PRINCIPLES OF PART II. cases an inequality would be no advantage or disadvantage to certain individuals more than to others; and therefore it could hardly have resulted from natural selection. We must attribute the inequality to the direct action of those unknown conditions, which with mankind lead to the males being born in a somewhat larger excess in certain countries than in others, or which cause the proportion between the sexes to differ slightly in legitimate and illegitimate births. Let us now take the case of a species producing from the unknown causes just alluded to, an excess of one sex-we will say of males-these being superfluous and useless, or nearly useless. Could the sexes be equalised through natural selection? vVe may feel sure, from all characters being variable, that certain pairs would produce a somewhat less excess of males over females than other pairs. ~rhe former, supposing the actual number of the offspring to remain constant, would necessarily produce more females, and would therefore be more productive. On the doctrine of chances a greater number of the offspring of the more productive pairs would survive; and these would inherit a tendency to procreate fewer males and more females. Thus a tendency towards the equalisation of the sexes would be brought about. But our supposed species would by this process be rendered, as just remarked, more productive ; and this would in many cases be far from an advantage; for whenever the limit to the numbers which exist, depends, not on destruction by enemies, but on the amount o~ food, increased fertility will lead to severer competiti~ n and t? most of the survivors being badly fed. In th1s case, If the sexes were equalised by an increase in the number of the females, a simultaneous decrease in the total number of the offsprino- would be benefic·ial b ' or even necessary, for the existence of the species; and CHAP. VIII. SEXUAL SELECTION. 317 this, I believe, could be effected through natural selec.:. tion in the manner hereafter to be described. The same train of reasoning is applicable in the above, as well as in the following case, if we assume that females instead of males are produced in excess, for such females from not uniting with males would be superfluous and useless. So it would be with polygamous species, if we assume the excess of female_s to be inordinately great. An excess of either sex, we will again say of the males, could, however, apparently be eliminated through natural selection in another and indirect manner, namely by an actual diminution of the males, without any increase of the females, and consequently without any increase in the productiveness of the species. From the variability of all characters, we may feel assured that some pairs, inhabiting any locality, would produce a rather smaller excess of superfluous males, but an equal number of productive females. When the offspring from the more and the less male-productive parents were all mingled together, none would have any .direct advantage over the others; but those that produced few superfluous males would have one great indirect advantage, namely that their ova or embryos would probably be larger and finer, or their young better nurtured in the \vomb and afterwards. ''re see this principle illustrated with plants; as those which bear a vast number of seed produce small ones; whilst those which bear comparatively few seeds, often produce large ones well-stocked with nutriment for the use of the seedlings.73 Hence the offspring of the parents which 73 I have often been struck with the fact, tho.t in several species of J>rimula the seeds in" the capsules which contained only a few were very much larger than the numerous seeds in the more productive <lapsules. |