DAR WIN ISM AND OTHER BRANCHES OF SCIENCE. 355 



century comes to be written, the interest will culminate 

 in the supreme discovery of Natural Selection. 



There are so many modifying circumstances to be taken 

 into account that it is not often easy to trace the actual 

 course of natural selection ; but the leading idea is so 

 simple that, once it is properly stated, I do not see how 

 any reasonable person can refuse his assent. There is a 

 well-known proverb, "As like as two peas," and at a 

 superficial glance two peas are no doubt very like each 

 other. They are like in their size, shape, and colour; 

 they are like in their internal structure; but, when we 

 look closely into the subject, no two peas are exactly alike. 

 Take any two peas from a sack, and after a brief examina- 

 tion we can detect innumerable points of difference. 

 Weighed in a careful balance, they have not the same 

 actual weight ; gauged with a pair of callipers, they have 

 not the same size ; and these differences extend to every 

 minute part of the structure. One pea will have more 

 nourishment stored up for the benefit of the future plant. 

 Another will be better able to resist hurtful influences. 

 That two peas should be so absolutely identical in every 

 feature as to be indistinguishable is an impossibility, or, 

 as a mathematician would say, the chances are infinitely 

 against such an occurrence. If we find that two peas are 

 never really alike, we shall also find that no two organisms 

 of any kind are really alike when attention is directed to 

 minute points of distinction. A shepherd will laugh to scorn 

 the idea that any two of his flock are so alike that they could 

 be mistaken. Even his dog knows better than that. A 

 poultry fancier will see in his pets conspicuous marks of 

 difference which are barely apparent to the unskilled eye. 



