It wasn't until the younger Darwin was back in England and read Thomas Malthus's Essay on the Principle of Population (which proposed that increases in food supply could never keep up with population growth for mathematical reasons) that the idea began to percolate through his mind that life is a perpetual struggle and that natural selection was the means by which some species prospered while others failed. Specifically what Darwin saw was that all organisms competed for resources, and those that had some innate advantage would prosper and pass on that advantage to their offspring. By such means would species continuously improve.
直到年轻的达尔文回到英格兰并读到托马斯·马尔萨斯的《人口论》（认为呈算术级增长的食物供给永远也满足不了呈几何级增长的人口）之后，进化论的观念才开始在他的心中萌生。他意识到，生命是一个持续不断的竞争的过程，自然选择决定了某些物种繁荣，某些物种衰败。说得具体一些，达尔文观察到，所有的生物都为了争夺资源而相互竞争，那些天生具有优势的生物才会繁荣昌盛，并且将这种优势遗传给他们的后代。通过这种方式，物种持续不断地得到了改进。

It seems an awfully simple idea — it is an awfully simple idea — but it explained a great deal, and Darwin was prepared to devote his life to it. "How stupid of me not to have thought of it!" T. H. Huxley cried upon reading On the Origin of Species. It is a view that has been echoed ever since.
这似乎是一种再简单不过的看法——这确实也是一个十分简单的看法，但是它解释了太多的问题，而达尔文准备将他的一生奉献给这种理论。在阅读《物种起源》时，T.H.赫胥黎曾喊着说：“我怎么这么愚蠢，竟然没有想到这一点！”从那以后，这种感叹声就一直不绝于耳。
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 (by which time its use had become too widespread to resist), 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.
有趣的是，在他的所有著作里，达尔文并没有使用“最适应者生存”这个词（虽然他确实对这个词由衷地赞赏）。它是1864年由赫伯特·斯宾塞在他的《生物学原理》一书里创造的，那是在《物种起源》发表5年以后。达尔文也没有使用“进化”这个词（那时这个词已经用得很广泛，有极大的诱惑力），而是代之以“后代渐变”。直到《物种起源》第6次印刷的时候，他才开始使用这个词。尤其重要的是，他的结论也绝不是他在加拉帕戈斯群岛期间注意到那里的效舌鸫的嘴多种多样，受到了启发才得出来的。