116 A PRIMER OF BIOLOGY 



Before we can answer this question we must look 

 at two series of phenomena of fundamental 

 importance, viz., those of heredity and those of 

 variation. 



It is a matter of common knowledge that an 

 organism produces an organism liker to itself 

 than to any other organism an oak tree pro- 

 duces an acorn, which in turn produces an 

 oak tree ; a lobster produces an egg, which in 

 turn becomes a lobster. The offspring inherits all 

 the fundamental characteristics of its parent 

 it is hereditarily like its parent. But neverthe- 

 less no offspring resembles its parent in every 

 particular ; it occasionally shows features which 

 recall characters of its grandparents, or even of some 

 farther back ancestor, and it also presents individual 

 idiosyncrasies of its own, which, so far as we can see, 

 are not traceable to any ancestor. We are accus- 

 tomed to say " as like as two peas " we might just 

 as well say " as unlike as two peas," for no two peas 

 are exactly alike. There are differences in colour, 

 in weight, in size, in form, in the number and shape 

 of the cells of which they are composed, in the contents 

 of these cells, and so on, and the plants arising from 

 them are also different from each other in every 

 detail, though we have no hesitation in identifying 

 both as pea plants. No child is precisely like either 

 parent though it may show characters present in 

 both ; each has an individuality of its own. Some 

 of these variations may be of such a kind as to lessen 

 its chances of success in the struggle before it ; some 

 may be, on the other hand, entirely in its favour. It 

 must be at once apparent that those individuals 

 which possess any variation giving them a superiority, 

 however little, over their fellows will, on the whole, 



