Evolution is supersolid. We even base the vaccine industry on it: When we troop into the doctor’s office each winter to get a flu shot — an inoculation against the latest evolved strains of the disease — we’re treating evolution as a law. So why not just say “the law of evolution”?
Best of all, it performs a neat bit of linguistic jujitsu. If someone says, “I don’t believe in the theory of evolution,” they may sound fairly reasonable. But if someone announces, “I don’t believe in the law of evolution,” they sound insane. It’s tantamount to saying, “I don’t believe in the law of gravity.”