vii LAW AND PRINCIPLE 189 



that evolution usually proceeds by taking advantage of 

 slight successive variations. This was the idea upon 

 which he never ceased working for twenty years, and 

 which culminated in the publication of his Origin of 

 Species, in 1859. 



By collecting all facts which bore in any way on the variation 

 of animals and plants under domestication and nature, some 

 light might perhaps be thrown on the whole subject. My first 

 note-book was opened in July, 1837. I worked on true Baconian 

 principles, and, without any theory, collected facts on a wholesale 

 scale, more especially with respect to domesticated productions 

 by printed inquiries, by conversation with skilful breeders and 

 gardeners, and by extensive reading. Charles Darwin. 



Variation is a common attribute of organic life ; no 

 two animals of the same kind are exactly alike in every 

 respect ; and the forms best adapted to particular 

 circumstances are the forms which survive longest and 

 carry on their kind. Life is always a struggle, and the 

 fittest for the time being are those which thrive best in 

 their surroundings. The intensity of the struggle for 

 existence, even in so large and open an arena as that 

 of the ocean, is shown by the small number of fish which 

 arrive at maturity in comparison with the immense 

 number of eggs produced. It is estimated that of the 

 five million or more eggs borne by a single codfish, all 

 except two or three meet with untimely deaths at 

 some stage of their career from the egg to the mature 

 adult. 



Applications of the principle of natural selection can 

 be found throughout the kingdom of animate Nature, 

 but we will mention one only. After a severe storm of 

 snow and sleet in North America, Prof. H. C. Bumpas 

 collected one hundred and thirty-four sparrows which had 

 been rendered insensible by the weather. Of these birds 



