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But would it not be much more simple and sublime to suppose that after the creation of the original animals, all their multifarious successions should arise from them by the operation of some fixed scientific law?This was one of his first ideas，a law which would do for biology what gravitation had done for astronomy.
那么假設最初的動物創造出來之后，它們所有的各種演替都由于某種固定不變的科學規律的作用而產生，豈不更簡便，更好？這是他最初的設想之一，一種如萬有引力定律之適用于天文學那樣的適用于生物學的普遍定律。
But what was the law? He tried to think it out, and almost succeeded. He noted that a variety of South American ostrich might have not been ‘well adapted, and thus perish'，while in a variety with favourable qualities ‘many might be produced’.This required the principle that some variations survive because they are adapted to changing circumstances and that the ‘death of species is a consequence of non-adaptation to circumstances ’.
可那究竟是條什么定律呢？他努力推究，幾乎獲得成功。他注意到，一種南美鴕鳥可能沒能“很好適應，因此消亡”，而在具有有利特性的品種身上“也許會產生出許多變種”。這就需要一種原理，即某些變異物種幸存是因為適應了變化的環境，而“物種的死亡是對環境不適應的結果。”
Darwin had almost worked out the ideas of natural selection and the survival of the fittest,but they did not become quite clear to him until the following year, 1838, when he happened to read Malthus，Essay on the Principle of Population.Malthus said that ‘Population，when unchecked, increases in a geometrical ratio ... This implies a strong and constantly operating check on population from the difficulty of subsistence... ’
達爾文幾乎得出了自然選擇與適者生存的理論，但直到次年，即1838年，這些想法才開始 變得明朗，當時他正好在讀馬爾薩斯的《人口論》。馬爾薩斯指出，“人口不受抑制時以幾何級 數增長。這意味著維持生計之艱難對人口所起的強有力的、長期的抑制作用。”
Darwin saw at once that ‘under these circumstances favourable variations would tend to be preserved and unfavourable ones to be destroyed. The result of this would be the formation ofa new species. Here then I had a theory by which to work ’.
達爾文馬上意識到，“在這種情況下有利的變異往往會保存下來，而不利的變異往往會遭毀滅。這一現象的結果會形成一個新的物種。這樣我就有了一種可以從事研究的理論了。”
Darwin established the evolutionary method by using it to explain the origin of species.But he also showed how to use it in many other directions.In his Descent of Man he showed how it could be applied in anthropology, and in The Expression of the Emotions in Man and Animals, to psychology.
達爾文確立了進化論，用以解釋物種起源。但他也展示了如何將進化論應用到許多其他方面。他在《人類由來》中表明了進化論在人類學領域的應用，在《人類和動物的表情》中顯示了在心理學領域的應用。
By showing that one species must have arisen from another, he raised the question of how, and thus founded the science of genetics. He explored this science in his Variation of Animals and Plants under Domestication, and said that ‘a grand and almost untrodden field of inquiry will be opened, on the causes and laws of variation, on correlation, on the effects of use and disuse, on the direct action of external conditions, and so on …’
通過展示一物種必自另一物種進化而來，他提出了怎樣進化的問題，由此建立了遺傳學。 他在《動物和植物在家養下的變異》中探究了遺傳學理論，指出“一個廣博的尚無人涉足的研究領域將得到開辟，這一領域將涉及變異的起因與規律、相互關系、運用與廢棄的結果、外部條件的直接作用，等等。”
