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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.
那么假设最初的动物创造出来之后，它们所有的各种演替都由于某种固定不变的科学规律的作用而产生，岂不更简便，更好？这是他最初的设想之一，一种如万有引力定律之适用于天文学那样的适用于生物学的普遍定律。
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 ’.
可那究竟是条什么定律呢？他努力推究，几乎获得成功。他注意到，一种南美鸵鸟可能没能“很好适应，因此消亡”，而在具有有利特性的品种身上“也许会产生出许多变种”。这就需要一种原理，即某些变异物种幸存是因为适应了变化的环境，而“物种的死亡是对环境不适应的结果。”
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... ’
达尔文几乎得出了自然选择与适者生存的理论，但直到次年，即1838年，这些想法才开始 变得明朗，当时他正好在读马尔萨斯的《人口论》。马尔萨斯指出，“人口不受抑制时以几何级 数增长。这意味着维持生计之艰难对人口所起的强有力的、长期的抑制作用。”
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 ’.
达尔文马上意识到，“在这种情况下有利的变异往往会保存下来，而不利的变异往往会遭毁灭。这一现象的结果会形成一个新的物种。这样我就有了一种可以从事研究的理论了。”
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.
达尔文确立了进化论，用以解释物种起源。但他也展示了如何将进化论应用到许多其他方面。他在《人类由来》中表明了进化论在人类学领域的应用，在《人类和动物的表情》中显示了在心理学领域的应用。
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 …’
通过展示一物种必自另一物种进化而来，他提出了怎样进化的问题，由此建立了遗传学。 他在《动物和植物在家养下的变异》中探究了遗传学理论，指出“一个广博的尚无人涉足的研究领域将得到开辟，这一领域将涉及变异的起因与规律、相互关系、运用与废弃的结果、外部条件的直接作用，等等。”
