environments-perhaps varying soil types or food sources. Over time, these genetic differences become so great that successful cross-fertilization can no longer take place. In behavioral isolation, related groups evolve differing behaviors such as specific mating rituals-that restrict the exchange of genes to members of the same group.两种基因型机制阻碍了相关群体中个体的基因交换。第一种基因型由前合子机械隔离机制阻止合子的生成。前合子隔离分两类:生态学的和行为学的。第一种情况,两个相关群体可能分别适应稍微不同的环境,如土壤类型或食物来源的变化。长时间,这些遗传差异变得很大而很难异体受精。而行为学隔离,相关的群组进化成不同的行为方式,例如,结婚仪式,从而限制了同群成员基因交流。