Similarly in a genome, unused genes are usually not removed, but gradually diverge from their originally functional sequence due to accumulated mutations. Viruses take the analogy one step further: we even speak of ‘computer viruses’, pieces of code that self-replicate, sometimes with the malign intent of the programmer. As with an infected computer, biological viruses, or the remains of them, can persist undetected in our genome as long as they do not interfere too drastically with normal function. In fact, it turns out that endogenous viruses are not the main malware in our genomes. They are
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