242 NATURAL SCIENCE [October 



selection only securing that the variation is a good one. The 

 natural selection of Darwin works in the same way : that is, it 

 isolates beneficial variations by killing off the others. It is not so 

 much natural selection as natural elimination ; for, as Professor 

 Lloyd Morgan has pointed out, 1 it is not by the survival of the 

 fittest, but by the elimination of the least fit, that new species are 

 made. Isolation by elimination must always tend to preserve 

 variations which are useful to the competing individuals, while 

 isolation by other means may preserve not only useful, but also 

 indifferent and even injurious, variations, as in the case of domesti- 

 cated animals and cultivated plants. 



Isolation by Selection — or natural selection in a restricted 

 sense — implies an outside agency as selector for whose benefit the 

 isolation is made. These cases of true natural selection are limited 

 to selection by insects. Several kinds of beetles, domesticated by 

 ants, have become blind, and some of them are unable to feed them- 

 selves. These variations are evidently injurious to the domesticated 

 animals, but useful to the ants, as they prevent the beetles from 

 running away. The sticky secretion of aphides must also be in- 

 jurious, if we may judge by the eagerness with which they allow the 

 ants to remove it ; and we must, therefore, suppose it to be due to 

 selection by the ants. But how the selection was made we do not 

 know. 



The structural growths which, in many flowers, necessitate the 

 visits of special insects to fertilise them, are also probably due to 

 natural selection in its narrow sense, for it is very doubtful whether 

 they are useful to the plants. In the first place the plants which 

 have the most elaborate apparatus for securing fertilisation by 

 certain insects only are uniformly rare ; while self-fertilising and 

 anemophilous plants are abundant. 2 Secondly, very few annual 

 plants, which must set seeds every year, have complicated flowers, 

 and some of these — such as the annual peas and beans — are also 

 self-fertilising. Thirdly, many perennial plants with elaborate 

 flowers have resorted to other means to secure fertilisation in case 

 insects fail to visit them. Fourthly, the great number and abund- 

 ance of plants, whose inconspicuous gamopetalous flowers show that 

 they have reverted from insect fertilisation, is a sufficient proof that 

 they have not suffered any harm by doing so. We must therefore 

 conclude that the elaborate flowers found in many of the so-called 

 entomophilous plants are quite unnecessary for their well-being, and, 

 indeed, must be sometimes harmful, for they render fertilisation 



1 " Animal Life and Intelligence," 2nd ed., ]>. 791. 



2 Henalow, "On the Self-Fertilisation of Plants," Trans. Linn. Sac, 2nd series 

 (Botany), vol. i., p. 317. 



