212 DARWINISM AND THE PROBLEMS OF LIFE 



by combination. It is clear that natural selection may 

 attain the same end by different means. When, for 

 instance, the herons began to seek their food at the 

 bottom of the water, selection favoured not only those 

 with long legs, but also those with long bills and long 

 necks. The end was reached by all three modifications, 

 and so they were equally selected. The continual 

 crossing of the three characters gave rise to the actual 

 herons, which have all three of them. 



Finally, we need not suppose that the co-adaptations 

 must arise simultaneously, and it is precisely in this that 

 the chief difficulty was found. Remember our illustra- 

 tion from the dice. We can easily get our ten sixes if 

 we throw until a six turns up, then leave this standing, 

 and throw again until another six appears, and so on 

 until we have got our ten sixes. 



Natural selection may act in the same way. In the 

 giant stag first large antlers were favoured ; they were, 

 of course, not immediately so heavy that the animals 

 with weaker skull and neck were incapacitated, because 

 all variations are small at first. When a race of stags 

 with large antlers had thus been formed, and continued 

 to increase, the time came when only the individuals 

 with strong skulls could carry the antlers with ease. 

 Then the thicker skulls were selected. Thus all the 

 co-adaptations might be selected successively ; even if 

 they were wanting at first, they were bound to appear 

 in the course of a long period, and would then be 

 favoured. But even if they were wanting at first, 

 the animals with the larger antlers were not necessarily 

 incapacitated. We must not forget that use in the 



