Affirming the consequent

Biological Parallel

'If poisonous, then brightly colored. This frog is brightly colored. Therefore, poisonous.' This is affirming the consequent—the logic reverses causation. Many harmless species are bright (mimics, sexual displays, camouflage contexts). The fallacy is taxonomically expensive: predators who reason this way eat safe food but also die from mimics' deception. Natural selection favors Bayesian reasoning: bright coloring increases probability of toxicity but doesn't guarantee it. Logic errors have fitness costs.