6 EVOLUTION THE KEY TO NATURE 



nineteenth centuries, it was quite easy to see that 

 burials had been going on for tens of millions of 

 years. And it was noticed that the deeper you went 

 the simpler the forms became and the more they 

 approached each other. The facts themselves sug- 

 gested that the animal-forms we know to-day, so 

 different from each other as they are, had common 

 ancestors in the past. Life was a great many- 

 branched tree, with a single root in the soil of "dim, 

 remote ages." 



Several writers had suggested this before Charles 

 Darwin became convinced of it in 1836, but that 

 patient and gifted naturalist took twenty years to 

 work out his theory and collect facts in support of it, 

 so that his Origin of Species, which was published in 

 1859, was irresistible. One set of scientific men after 

 another now began to apply the principle of evolution, 

 or gradual growth, and each department of nature 

 which they studied was lit up as it had never been 

 before. Sir Isaac Newton had traced a remarkable 

 unity in lifeless nature when he discovered the law 

 of gravitation. A far more intimate unity was now 

 discovered, both in living and lifeless nature, in the 

 light of the new truth. 



Everything known to us had been evolved. From 

 distant suns to our social and religious institutions, 

 from diamonds or oceans to the human struggles of 

 to-day and the ideals of to-morrow, the whole contents 

 of the known universe fell into one grand and intel- 



