A glacier could thrust across their range, for example.The isolated population evolves new genes, and some of those new genes may make interbreeding difficult or impossible.

• 举例来说，冰河可以分割物种的分布范围，受到隔离的族群会演化出新的基因，而其中一些新的基因可能导致不同族群间不易或完全无法交配。