Author: Bill Bryson
Interestingly, Darwin didn't use the phrase "survival of the fittest" in any of his work (though he did express his admiration for it). The expression was coined five years after the publication of On the Origin of Species by Herbert Spencer in Principles of Biology in 1864. Nor did he employ the word evolution in print until the sixth edition of Origin, preferring instead "descent with modification." Nor, above all, were his conclusions in any way inspired by his noticing, during his time in the Galapagos Islands, an interesting diversity in the beaks of finches. The story as conventionally told is that Darwin, while traveling from island to island, noticed that the finches' beaks on each island were marvelously adapted for exploiting local resources- that on one island beaks were sturdy and short and good for cracking nuts, while on the next island beaks were perhaps long and thing and well suited for winkling food out of crevices - and it was this that set him to thinking that perhaps the birds had not been created this way, but had in a sense created themselves.
In fact, the birds had created themselves, but it wasn't Darwin who noticed. At the time of the Beagle voyage, Darwin was fresh out of college and not yet an accomplished naturalist and so failed to see that the Galapagos birds were all of a type. It was his friend the ornithologist John Gould who realized that what Darwin had found was lots of finches with different talents.