As more individuals are produced than can possibly survive , there must … be a struggle for existence , either one individual with another of the same species , or with the individuals of distinct species, or with the physical conditions of life.
当个体的数量超过自然能够接受的程度时，他们必为了生存而竞争，他们与物种内的其他个体竞争，或者与其他物种的个体竞争，或者与生活的自然环境竞争。

——Charles Darwin, Origin of Species
——达尔文，《物种起源》