EFFECT OF SELECTION 137 
methods of evolution are now known to be available, 
the burden of proof of this proposition seems to 
lie with those who maintain the all-important influ- 
ence of continuous variation and selection. At present 
we are free to reply in the words of Malthus, who long 
ago protested against the extravagant powers which 
were ascribed to the selection of small differences. 
‘I have been told,’ Malthus writes, ‘that it is a 
maxim among some of the improvers of cattle that 
you may breed to any degree of nicety you please, 
and they found this maxim upon another, which is, 
that some of the offspring will possess the desirable 
qualities of the parents in a greater degree. In the 
famous Leicestershire breed of sheep, the object is to 
procure them with small heads and small legs. Pro- 
ceeding upon these breeding maxims, it is evident that 
we might go on until the heads and legs were evan- 
escent quantities ; but this is so palpable an absurdity 
that we may be quite sure the premises are not just, 
and that there really is a limit, though we cannot see 
it or say exactly where it is.’ * 
The only recorded example I am aware of in the 
case of animals, which shows the result of long-con- 
tinued selection acting upon a quantitative character, 
is afforded by the case of the American trotting-horse. 
In this case it appears highly probable that we are 
dealing with a character which varies in a strictly 
continuous fashion. In his book upon ‘ The Trotting 
and Pacing Horse in America,’ Hamilton Busbey 
gives a table from which the diagram on p. 138 
* ‘Essay on Population,’ 6th ed., vol. ii., p. 11. 
