““Vengefulness signals that a breach in contract will not be tolerated at any cost, even at the price of the avenging individual’s own life or fortune. In each case, the emotion was presumably selected in response to a statistical range of specific ancestral problems that required abeyance of short-term calculations of selfinterest. Such emotions would have to be “eruptive” to be believed and to convince others, that is, sincerely out of control, hard to fake, and unsuited to apparent self-interest.””
