It’s also intriguing to consider why crabs keep on trusting claw size as a reliable clue to how they’ll fare in a fight. There’s good reason to think that while the rule isn’t perfect, it works well enough. The chances are low that a male crab will encounter a bluff. It’s better to err on the side of safey in a fight than to err on the side of distrust. And so the crabs allow deception to thrive.

That is a nice balance at work. If replacement claws were more common, there would be more successful challenges of these crabs, and pressure to evolve stronger replacement claws. If crabs didn’t trust the rule, they would waste energy on more challenges they cannot win. It’s a sort of crustacean cost-benefit analysis.