The Making of Species 



On the other hand, it is significant that just 

 where the links are most needed they are missing. 

 For example, the splint bones of the horse, taken 

 in conjunction with the feet of existing tapirs, 

 which have four toes in front and three behind, 

 would have led us to infer, without the help of 

 the geological record, that the horse was a 

 descendant of a polydactyle ancestor. When, 

 however, we come to the origin of birds, bats, 

 and whales, palaeontology fails to give us any 

 assistance, so that we are in the dark as to the 

 origin of such really important modifications. 



7. The swamping effects of inter-crossing is 

 an objection which has been repeatedly urged 

 against the Darwinian theory. 



This objection is not so serious as it appears 

 at first sight. Darwin and Wallace maintain, 

 firstly, that natural selection acts by eliminating all 

 individuals except those which present favourable 

 variations. The favoured few alone survive and 

 mate with one another, so that there is here no 

 question of the swamping effects of inter-crossing, 

 none but well-adapted individuals being left 

 to mate with one another. 



The objection gains greater force when directed 

 against the theory that evolution proceeds by 

 sudden jumps. But in this connection we must 

 bear in mind that the experiments of Mendel 

 and his followers have demonstrated that some 

 of the offspring of crosses may resemble their 



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