But translating selection pressure into evolutionary change requires another crucial ingredient: the variation observed in the trait should be caused at least in part by genetic differences. Indeed, evolution is possible only if the resemblance between related individuals has a genetic basis, and is not simply a reflection of a shared environment.
但选择压力转化为进化演变还需要另外一个关键元素：显性的特质变化至少应当部分归结于基因的不同。其实，只有当相关个体相似度具备遗传基础，而并非仅仅是共同环境使然时进化才成为可能。