THE INADEQUACY OF "NATURAL SELECTIONS 23 



of a rodent's tail as that which, by successive increases, produces 

 the trowel-shaped tail of the beaver, no advantage will be derived 

 unless there also take place certain modifications in the bulks and 

 shapes of the adjacent vertebrse and their attached muscles, as 

 well, probably, as in the hind limbs, enabling them to withstand 

 the reactions of the blows given by the tail. And the question is, 

 by what process these many parts, changed in different degrees, 

 are co-adapted to the new requirements whether variation and 

 natural selection alone can effect the readjustment. There are 

 three conceivable ways in which the parts may simultaneously 

 change: (1) they may all increase or decrease together in like 

 degrees ; (2) they may all simultaneously increase or decrease in- 

 dependently, so as not to maintain their previous proportions or 

 assume any other special proportions ; (3) they may vary in such 

 ways and degrees as to make them jointly serviceable for the new 

 end. Let us consider closely these several conceivabilities. 



And first of all, what are we to understand by co-operative 

 parts ? In a general sense, all the organs of the body are co- 

 operative parts, and are respectively liable to be more or less 

 changed by change in any one. In a narrower sense, more directly 

 relevant to the argument, we may, if we choose to multiply diffi- 

 culties, take the entire framework of bones and muscles as formed 

 of co-operative parts; for these are so related that any consider- 

 able change in the actions of some entails change in the actions of 

 most others. It needs only to observe how, when putting out an 

 effort, there goes, along with a deep breath, an expansion of the 

 chest and a bracing up of the abdomen, to see that various muscles 

 beyond those directly concerned are strained along with them. 

 Or, when suffering from lumbago, an effort to lift a chair will 

 cause an acute consciousness that not the arms only are brought 

 into action, but also the muscles of the back. These cases show 

 how the motor organs are so tied together that altered actions of 

 some implicate others quite remote from them. 



But without using the advantage which this interpretation of 

 the words would give, let us take as co-operative organs those 

 which are obviously such the organs of locomotion. What, then, 

 shall we say of the fore and hind limbs of terrestrial mammals, 

 which co-operate closely and perpetually ? Do they vary together ? 

 If so, how have there been produced such contrasted structures as 

 that of the kangaroo, with its large hind limbs and small fore 

 limbs, and that of the giraffe, in which the hind limbs are small 

 and the fore limbs large how does it happen that, descending 

 from the same primitive mammal, these creatures have diverged 

 in the proportions of their limbs in opposite directions ? Take, 

 again, the articulate animals. Compare one of the lower types, 

 with its rows of almost equal-sized limbs, and one of the higher 



