Two things about these genomes have sparked unwarranted surprise. The first is that mammal genomes contain rather few genes: recent estimates count a little under 20,000 in humans. And the second is that they are so similar to each other. Human dignity seemed to demand that we should have far more genes than a tiny mouse. And shouldn’t it be absolutely larger than 20,000 anyway? This last expectation has led people, including some who should know better, to deduce that the ‘environment’ must be more important than we thought, because there aren’t enough genes to specify a body. That really is
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