If the individual populations'environments were exerting strong selective pressure, such differences should have been apparent.

但如果某一人群的环境真正具有很强的选择压力那么上述差异会很明显.

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In a large population where the selective pressure is strong, such mutations are likely be eliminated.

在选择压力强的大规模种群中, 这样的变异可能被淘汰.

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