【英语时差8,16】M&M巧克力豆与遗传漂变（下）

（单词翻译）

Every time an animal mates, its offspring receives a mixed bag of genes², half from its mother and half from its father. If the father and the mother share many of the same genes, their offspring will receive doubles of some of them. The doubles don’t help, and they mean that some other gene¹ that could have been passed on wasn’t. Think of the M&Ms. At the point where you failed to pull a red out of the bag, you have lost one gene. If your mate doesn’t have that gene either, then your descendants will never have it. Low populations of animals means less genetic³ variation, which means genetic drift is more likely. If the gene that gets lost was critical to the survival of the species, they might begin dying off altogether.