THE INADEQUACY OF "NATURAL SELECTIONS 27 



probability that the many required changes of shape, as well as 

 of size, in bones will each of them be effected before all the others 

 are lost again ? If the probabilities against success are incalcu- 

 lable, when we take account only of changes in the size of parts, 

 what shall we say of their incalculableness when differences of 

 form also are taken into account ? 



" Surely this piling up of difficulties has gone far enough " ; the 

 reader will be inclined to say. By no means. There is a difficulty 

 immeasurably transcending those named. We have thus far 

 omitted the second half of the leap, and the provisions to be made 

 for it. After ascent of the animaFs body comes descent ; and the 

 greater the force with which it is projected up, the greater is the 

 force with which it comes down. Hence, if the supposed creature 

 has undergone such changes in the hind limbs as will enable 

 them to propel it to a greater height, without having undergone 

 any changes in the fore limbs, the result will be that on its de- 

 scent the fore limbs will give way, and it will come down on its 

 nose. The fore limbs, then, have to be changed simultaneously 

 with the hind. How changed ? Contrast the markedly bent hind 

 limbs of a cat with its almost straight fore limbs, or contrast the 

 silence of the upward spring on to the table with the thud which 

 the fore paws make as it jumps off the table. See how unlike the 

 actions of the hind and fore limbs are, and how unlike their 

 structures. In what way, then, is the required co-adaptation to 

 be effected ? Even were it a question of relative sizes only, there 

 would be no answer ; for facts already given show that we may 

 not assume simultaneous increases of size to take place in the hind 

 and fore limbs ; and, indeed, a glance at the various human races, 

 which differ considerably in the ratios of their legs to their arms, 

 shows us this. But it is not simply a question of sizes. To bear 

 the increased shock of descent the fore limbs must be changed 

 throughout in their structures. Like those in the hind limb, the 

 changes must be of many parts in many proportions ; and they 

 must be both in sizes and in shapes. More than this. The scapu- 

 lar arch and its attached muscles must also be strengthened and 

 remolded. See, then, the total requirements. We must suppose 

 that by natural selection of miscellaneous variations, the parts of 

 the hind limbs shall be co-adapted to one another, in sizes, shapes, 

 and ratios ; that those of the fore limbs shall undergo co-adapta- 

 tions similar in their complexity, but dissimilar in their kinds ; 

 and that the two sets of co-adaptations shall be effected pari 

 passu. If, as may be held, the probabilities are millions to one 

 against the first set of changes being achieved, then it may be 

 held that the probabilities are billions to one against the second 

 being simultaneously achieved, in progressive adjustment to the 

 first. 



