378 
TROPICAL NATURE 
v 
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 
