A fitness payoff is the value an action carries for survival and reproduction, measured for a particular organism in a particular state. The same slice of world can carry wildly different payoffs. A pool of water is worth a great deal to a thirsty animal and can be lethal to one already waterlogged and cold. The payoff is not a property of the water. It is a relation between the creature, its condition and the thing.
This is the quiet engine under the fitness-beats-truth result. If payoffs were just a stand-in for the true state of the world, tracking them would amount to tracking truth, and perceiving reality would come along for free. But payoffs depend on the organism's state as much as on the world, so a perception tuned to payoffs and a perception tuned to truth pull apart. Evolution, following the payoffs, walks away from the truth without ever intending to.
The jewel beetle is a clean illustration. Its perceptual rule tracked a fitness payoff, mate here, and did so well for a long time. The rule never encoded what a female beetle actually is. It encoded a payoff signal: dimpled, glossy, brown, bigger is better. When a beer bottle hit that signal harder than a real female, the payoff logic followed the bottle, because the payoff was all it had ever been reading.
Fitness payoffs explain why a perfectly reliable perception can still be false. Reliability and truth are not the same virtue. A sense can lock onto a payoff signal for a hundred thousand years and be wrong about the world the entire time, right up until the environment shifts and the gap shows. That gap, when it opens, is where illusions become visible.
