FOOT-NOTES TO EVOLUTION. 
I. 
THE KINSHIP OF LIFE. 
No one with good eyes and brains behind them has 
ever looked forth on the varied life of the world, on 
forest or meadow or brook or sea, with- 
What is the out at least once asking himself the ques- 
ory ree tion, “ What is the cause of Nature’s end- 
i less variety ?”” We see many kinds of 
birds and trees and insects and fishes and flowers and 
blades of grass, and yet when we look closely we find not 
one blade of grass in the meadow quite like another blade. 
The green cloak which covers the brown earth is the 
shield under which millions of organisms, brown or 
green, carry on their life work; yet not one organism 
in the world in body or mind is the exact measure of 
its neighbour. But with all this the real variety in life 
is far greater than that which appears. 
Each kind of animal or plant, that is, each set of 
forms which in the vicissitudes of the ages has become 
segregated and set off from its neigh- 
bours, is called in biology a species. 
The number of these species is great 
beyond any ordinary conception. I have an old book 
in my library, the tenth edition of the Systema Nature, 
I 
What is a 
species ? 
