CH. XLI. DARWIN'S THEORY. 463 



all animals are only different branches from one stem, yet 

 this could only be a mere speculation, unless some one 

 could point out what has made them differ so much from 

 each other. Lamarck, as we have seen, could not do this, 

 and therefore his suggestion was passed by ; and it was not 

 till five -and -twenty years ago that two naturalists, Mr. 

 Darwin and Mr. Wallace, discovered a law which is cer- 

 tainly true in itself, and which accounts for many of the 

 facts. Their theory, which we must now consider, was so 

 new that it was opposed on all sides, just as the Copernican 

 theory was opposed in the sixteenth century, the circulation 

 of the blood in the seventeenth century, and the theory of 

 combustion, which overturned phlogiston, in the eighteenth 

 century. We live in the midst of the discussion about the 

 origin of species, yet even within the short space of a 

 quarter of a century it has almost outlived opposition, and 

 there is scarcely a naturalist of note who does not in one 

 form or another accept the Darwinian theory, which we 

 must now try to understand. 



Theory that Natural Selection has caused the 

 various kinds of Plants and Animals to differ per- 

 manently from each other, Darwin, 1809-1882. 

 The Theory of Natural Selection, or the Darwinian theory 

 as it is often called, was chiefly worked out by the great 

 naturalist Chailes Darwin, who was born in 1809 and died 

 in 1882. When he was only two -and -twenty, Mr. Darwin 

 went in her Majesty's ship * Beagle ' to survey the coast of 

 South America and sail round the globe ; and on his return 

 he wrote an account of the geology and natural history of the 

 countries he had visited. He tells us himself that even so 

 early as this he noticed many facts which seemed to him to 

 throw light on the difficult question of the origin of the dif- 

 ferent species of plants and animals; and he spent twenty years 



