Method of Origin of New Species and Structures 407 



Variation. —It is a matter of familiar knowledge that all 

 living things, or the structures they produce, even the most 

 closely-related, are different from one another, — to such a degree, 

 indeed, as to justify the common saying that no living thing 

 is exactly like any other living thing. The differences, or vari- 

 ations, affect every possible feature, — size, form, color, texture, 

 etc., and occur in every possible direction; and some of them 

 at least are inherited from the parents and transmissible to 

 offspring. 



Over-production. —All living beings possess a power of repro- 

 duction not only sufficient to replace the individuals which die, 

 but also to increase greatly their numbers. Moreover, the rate of 

 increase, in even the slowest breeding forms, is surprisingly rapid, 

 while with most kinds it is enormously so. Thus, a plant which 

 produces only ten seeds a year (and few produce so very small a 

 number), would have one billion descendants within ten years, 

 and would soon cover the earth to the exclusion of all others could 

 its increase proceed without hindrance. 



Struggle for Existence. — Although every kind of plant and of 

 animal is thus tending to increase enormously in numbers, never- 

 theless in a broad way those numbers remain stationary from one 

 generation to another. Local fluctuations do of course occur, for 

 some kinds of plants or animals are on the way to extinction, 

 while others, such as weeds or insect pests, have periods of rapid 

 expansion; but in general it is true that there are no more of any 

 particular kinds, — lichens, goldenrods, thrushes or squirrels, — in 

 a given region one year than another. The reason thereof is 

 obvious enough, — the world is already as full of animals and 

 plants as there is food or room for, and new ones can find a place 

 only as the old ones die out. This, then, is the situation; — that 

 while great numbers of plants and animals are born into the world 

 in each generation, there is only room or food for an occasional 

 one of the number. But as each and every one of the individuals 

 thus born has an equal right and impulse to survive and possess 



