英语时差：M&M巧克力豆与遗传漂变（上）

We’ve discussed before how endangered species are at risk from the increased likelihood of inbreeding, which leads to unhealthy offspring. But there’s another danger to letting the numbers of animals in a given species become too low. It’s called genetic drift. Genetic drift is the term biologists use to describe the gradual loss of certain genes from a species–genes that may have been very important for that species’ survival. How Can Animals Lose Genes? It’s kind of like reaching into a bag of M&Ms. If you take out a hundred M&Ms you are sure to get all the colors at least once. If you only take out ten, you may well miss a color. And if by chance you haven’t missed a color, try it again. Very soon you will come up with, say, no reds.