378 TROPICAL NATURE 



Natural Selection as neutralising Sexual Selection 

 There is also a general argument against Mr. Darwin's 

 views on this question, founded on the nature and potency 

 of " natural " as opposed to " sexual " selection, which appears 

 to me to be of itself almost conclusive as to the whole matter 

 at issue. Natural selection, or the survival of the fittest, 

 acts perpetually and on an enormous scale. Taking the off- 

 spring of each pair of birds as, on the average, only six 

 annually, one-third of these at most will be preserved, while 

 the two-thirds which are least fitted will die. At intervals of 

 a few years, whenever unfavourable conditions occur, five- 

 sixths, nine-tenths, or even a greater proportion of the whole 

 yearly production are weeded out, leaving only the most 

 perfect and best adapted to survive. Now unless these sur- 

 vivors are, on the whole, the most ornamental, this rigid 

 natural selection must neutralise and destroy any influence 

 that may be exerted by female selection. The utmost that 

 can be claimed for the latter is, that a small fraction of the 

 least ornamented do not obtain mates, while a few of the 

 most ornamented may leave more than the average number of 

 offspring. Unless, therefore, there is the strictest correlation 

 between ornament and general perfection, the more brightly 

 coloured or ornamented varieties can obtain no permanent 

 advantage ; and if there is (as I maintain) such a correlation, 

 then the sexual selection of colour or ornament, for which 

 there is little or no evidence, becomes needless, because 

 natural selection, which is an admitted vera causa, will itself 

 produce all the results. 



In the case of butterflies the argument becomes even 

 stronger, because the fertility is so much greater than in 

 birds, and the weeding-out of the unfit takes place, to a great 

 extent, in the egg and larva state. Unless the eggs and 

 larvae which escaped to produce the next generation were 

 those which would produce the more highly-coloured butter- 

 flies, it is difficult to perceive how the slight preponderance 

 of colour sometimes selected by the females should not be 

 wholly neutralised by the extremely rigid selection for other 

 qualities to which the offspring in every stage are exposed. 

 The only way in which we can account for the observed facts 



