他们认为这两个物种是在100多万年前分化出来的。
The two species are thought to have split over one million years ago.
研究表明粳稻和籼稻大约在3900年前才由同一种水稻分化成两种不同的亚种。
The study indicates that the japonica and indica sub-species split apart from each other about 3, 900 years ago.
例如，人头虱是500万年前当人类祖先与黑猩猩分化时从黑猩猩身上的虱子进化来的。
The human head louse, for instance, evolved from the chimpanzee louse when the ancestors of humans and chimps split apart some five million years ago.
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