CH. XL. DARWIN* S THEORY. 425 



same bones, and why some should have parts remaining in 

 their body which are no longer of any use ; and lastly, it 

 would explain why naturalists have so much difficulty in 

 distinguishing nearly related species. 



But though these reasons made it seem very likely that 

 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 

 about sixteen years ago that two naturalists, Mr. Darwin and 

 Mr. Wallace, discovered a law which is certainly tnie in 

 itself, and which accounts for many of the facts. Their 

 theory, which we must now consider, is so new that it has 

 been 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 spe- 

 cies, and it will only be our great-grandchildren who will be 

 able to talk of the Darwinian theory in the way in which 

 we talk of the discoveries of past centuries ; but you ought 

 at least to understand what this theory is, for it forms an 

 era in the history of science. 



Darwin's Theory that Natural Selection has caused the 

 various kinds of Plants and Animals to differ widely and 

 permanently from each other. The theory of Natural Selec- 

 tion, or the Darwinian theory as it is often called, has been 

 chiefly worked out by a'great living naturalist, Mr. Charles 

 Darwin, who was born in 1809. 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 ; 



