An inflexible moral compass evolved to prevent costly defection errors.

Evidence

Such invariance was ostensibly selected for because an inflexible moral compass is thought to preclude both erroneously trading the larger long-term gains of mutualism for the smaller short-term gains of defection, and erroneously underestimating the likelihood of getting caught in the act. — Nicolas Baumard, A mutualistic approach to morality, 391

Categorization

• DEFINE: This is the mechanistic rationale for the invariant-moral-compass hypothesis — the target the authors then attack.