258 DARWINISM AND THE PROBLEMS OF LIFE 



appear simultaneously, as we saw in the instance of 

 the heron, in which one animal is favoured on account 

 of the length of its neck, another on account of the 

 length of its bill, and their offspring may inherit both 

 features. In this way amphimixis may easily bring 

 about a difference between two similar structures. A 

 hare, for instance, may inherit short fore legs from a 

 short-legged mother and long hind legs from a long- 

 legged father ; and as this combination is useful in view 

 of its leaping, it may be further selected. Thus co- 

 adaptations are facilitated and accelerated by amphimixis ; 

 the animals that are subject to it will be selected first, 

 and so we can see why amphimixis would be retained 

 in most animals, and why it is so wide-spread. 



But it is also useful to organisms in another respect. 

 When an organ varies in any animal — let us say it becomes 

 larger — it may, of course, become smaller in the next 

 generation, but may just as well become larger. Many 

 experts believe, in fact, that there are definite directions 

 of variation ; that some internal or external principle 

 often presses them in the direction they have once 

 taken. We will discuss later on the possibility of this, 

 but we can in any case imagine that variations, especially 

 those that are only in two opposite directions, may take 

 the same direction for some time. 



If any organ does vary in this way it may very often 

 be injurious to its possessor and bring about its 

 destruction. Excessive variations of this kind must 

 often appear, as chance may frequently lead to the 

 variation of an organ in a particular direction during 

 several generations. Amphimixis prevents animals from 



