Coadaptation 33 
to weigh down the animal altogether. It is inconceivable, he says, 
that so many processes of selection should take place simultancously, 
and we are therefore forced to fall back on the Lamarckian factor of 
the use and disuse of functional parts. And how, he asks, could 
natural selection follow two opposite directions of evolution in 
different parts of the body at the same time, as for instance in the 
case of the kangaroo, in which the forelegs must have become 
shorter, while the hind legs and the tail were becoming longer and 
stronger ? 
Spencer’s main object was to substantiate the validity of the 
Lamarckian principle, the cooperation of which with selection had 
been doubted by many. And it does seem as though this principle, 
if it operates in nature at all, offers a ready and simple explanation 
of all such secondary variations. Not only muscles, but nerves, bones, 
sinews, in short all tissues which function actively, increase in strength 
in proportion as they are used, and conversely they decrease when 
the claims on them diminish. All the parts, therefore, which depend 
on the part that varied first, as for instance the enlarged antlers of the 
Irish Elk, must have been increased or decreased in strength, in 
exact proportion to the claims made upon them,—just as is actually 
the case. 
But beautiful as this explanation would be, I regard it as un- 
tenable, because it assumes the transmissibility of functional modi- 
fications (so-called “acquired” characters), and this is not only 
undemonstrable, but is scarcely theoretically conceivable, for the 
secondary variations which accompany or follow the first as corre- 
lative variations, occur also in cases in which the animals concerned 
are sterile and therefore cannot transmit anything to their de- 
scendants. This is true of worker bees, and particularly of ants, and 
I shall here give a brief survey of the present state of the problem as 
it appears to me. 
Much has been written on both sides of this question since the 
published controversy on the subject in the nineties between Herbert 
Spencer and myself. I should like to return to the matter in detail, 
if the space at my disposal permitted, because it seems to me that 
the arguments I advanced at that time are equally cogent to-day, 
notwithstanding all the objections that have since been urged against 
them. Moreover, the matter is by no means one of subordinate 
interest ; it is the very kernel of the whole question of the reality 
and value of the principle of selection. For if selection alone does 
not suffice to explain “harmonious adaptation” as I have called 
Spencer’s Coadaptation, and if we require to call in the aid of the 
Lamarckian factor it would be questionable whether selection could 
explain any adaptations whatever. In this particular case—of worker 
D. 3 
