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The only genetic changes in humans we ever hear about are those producing diseases such as cystic fibrosis. Has anyone identified any genetic changes within recent generations that make individuals possessing them “more fit” to thrive in today’s environment? Would we even know these changes if we saw them? And would we consider them normal for healthy humans?

Colin Bamforth, Altrincham, Cheshire, UK

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This article appeared in print under the headline “Selected selections”