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, paleontology 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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