340 HABIT AND INTELLIGENCE. [cHAP. 



tion and highest organisms have on the whole the least fecundity. Com- 

 fecundity ^^^^ ^-j^^ comparatively small number of young produced by 

 opposed, birds and Mammalia with the thousands of eggs produced by 

 some fishes and many insects, and the countless germs of the 

 Bearing of lowest animals and plants. Might it not be expected, that 

 nataraT °^ whatever is gained in the chance of leaving offspring by ad- 

 selection, vanced organization wUl on the average be lost by diminished 

 fecundity ; that the greater fecundity of the inferior types will 

 give them as good a chance of leaving offspring as the superior 

 ones ; and that the superior and the inferior species will thus 

 be in the long run evenly matched in the battle of life, giving 

 the superior ones no permanent advantage 1 



This would be so if all other things were equal. But all 

 other things do not remain equal. The advantage of any 

 favourable variation to a race consists generally either in greater 

 facility of obtaining food, or in greater facility of escaping 

 enemies ; and either abundant food or tranquillity of Life will 

 tend to increase fecundity. So that advance in grade of 

 organization, though it wUl entail diminished fecundity as its 

 direct effect, wUl tend to counteract this effect in an indirect 

 way, namely by placing the organism in external circumstances 

 favourable to its fecundity. 



In such a question, verification by observation or experiment 

 is totally out of the question. But the above reasoning, con- 

 sidered merely as reasoning from what data we have, is, I think, 

 sound and satisfactory. It may be well to put it into an 

 algebraic form. 

 Algebraic Call grade of organization x, and fecundity y. Suppose, what 

 statement, jg approximately true, that the chance of surviving and leaving 

 offspring is proportionate to their product xy ; and suppose, 

 what is also approximately true, that, other things being equal, 

 the values of x and y are inversely as each other ; then, other 

 things being equal, xy wiU be a constant quantity, and no 

 increase in the value of x from any favourable variation will 

 increase the chance of leaving offspring. Call now abundance 

 of nutrition a. "Within limits, the value of y, as already shown, 

 wUl increase with that of a, and the value of a wiU increase 

 with that of a; ; so that any increase of the value of x from 

 spontaneous variation will tend to increase that of y, and con- 

 sequently of the product x y ; while, on the contrary, no increase 

 of the value of y will have any tendency to increase that of 

 either x ox xy. 



