1 88 THE TRANSMISSION OF VARIATIONS. 



advantage of by man. Artificial selection of varieties has 

 long been resorted to for breeding purposes. The judicious 

 selection and transmission through successive generations 

 of small individual differences has resulted in the production 

 of many of the varieties of domestic animals and plants 

 with which all are familiar. 



Nature, with precisely the same effect, has preserved 

 the favoured varieties in the fact that those animals and 

 plants which have not been adapted to changing conditions, 

 or have not been prepared to successfully meet the never 

 ceasing contest for existence, or which have varied in a 

 direction unfavorable for the strife, have succumbed ; whilst 

 their better favoured rivals have survived and been preserved. 

 In every geological formation which contains organic 

 remains and in all parts of the world, the unimpeachable 

 testimony of the rocks supports and confirms this great 

 truth. 



But it must be remembered that although new species 

 may be the result of natural selection it does not follow 

 that natural selection shall of necessity always produce new 

 species. This is evidenced by the persistence of some 

 forms of both animal and vegetable life through long 

 periods of geological time, during which little or no 

 structural modifications have taken place, as is especially 

 the case amongst some of the lower forms of both kingdoms. 



The fact that variations occur and persist which do not 

 give the varying forms any special advantage has been 

 raised as an objection to the theory of natural selection. 

 There does not however seem to be any real difficulty in 

 the matter, variations do and must take place which are 

 merely passive or negative, neither advantageous nor 

 detrimental and which yet persist. The remarkable modi- 

 fications which occur in the colour bands and markings 

 on the shells of the mollusca arc indicative of this. In the 



