When a variation is of the slightest use to any being, we cannot tell how much to attribute to the accumulative action of natural selection, and how much to the definite action of the conditions of life.

当变异对任何生物有丝毫用处时， 我们无法判断多少归因于自然选择的累积作用， 多少归因于生活条件的确定作用。