达尔文《物种起源》：
But the struggle almost invariably will be most severe between the individuals of the same species, for they frequent the same districts, require the same food, and are exposed to the same dangers.
不过最剧烈的斗争，差不多总是发生在同种的个体，因为它们居住在同一地域，需要同样食料，遭受同样威胁。
原文：
But the struggle almost invariably will be most severe between the individuals of the same species, for they frequent the same districts, require the same food, and are exposed to the same dangers. In the case of varieties of the same species, the struggle will generally be almost equally severe, and we sometimes see the contest soon decided.
不过最剧烈的斗争，差不多总是发生在同种的个体，因为它们居住在同一地域，需要同样食料，遭受同样威胁。在同种的变种之间，其斗争的剧烈，大概与此相等，并且有时在短期内即见胜负。
