A mutation that reverses the effect of a previous one (called a back mutation) could at one stroke revive a complex function that had been earlier shut off. If you didn’t know it was a back mutation you might be tempted to think it added a lot of information to the genome. But once you know that a single mutation cannot add more than one bit of information, you know that the complexity must have already been in the genome. The mutation must have turned ‘ON’ what had been an existing, but dormant, system.

Author: Lee Spetner