Center for Evolutionary Psychology

Genetic relatedness is a fundamental determinant of social behavior across species. Over the last few
decades, researchers have been investigating the proximate psychological mechanisms that enable
humans to assess their genetic relatedness to others. Much of this work has focused on identifying cues
that predicted relatedness in ancestral environments and examining how they regulate kin-directed
behaviors. Despite progress, many basic questions remain unanswered. Here we address three of these
questions. First, we examine the replicability of the effect of two association-based cues to relatedness—
maternal perinatal association (MPA) and coresidence duration—on sibling-directed altruism. MPA, the
observation of a newborn being cared for by one’s mother, strongly signals relatedness, but is only
available to the older sibling in a sib-pair. Younger siblings, to whom the MPA cue is not available,
appear to fall back on the duration of their coresidence with an older sibling. Second, we determine
whether the effects of MPA and coresidence duration on sibling-directed altruism obtain across cultures.
Last, we explore whether paternal perinatal association (PPA) informs sibship. Data from six studies
conducted in California, Hawaii, Dominica, Belgium, and Argentina support past findings regarding the
role of MPA and coresidence duration as cues to siblingship. By contrast, PPA had no effect on altruism.
We report on levels of altruism toward full, half, and step siblings, and discuss the role alternate cues
might play in discriminating among these types of siblings.

There is substantial evidence from archaeology, anthropology, primatology, and psychology indicating that humans have a long evolutionary history of war. Natural selection, therefore, should have designed mental adaptations for making decisions about war. These adaptations evolved in past environments, and so they may respond to variables that were ancestrally relevant but not relevant in modern war. For example, ancestrally in small-scale combat, a skilled fighter would be more likely to survive a war and bring his side to victory. This ancestral regularity would have left its mark on modern men's intergroup psychology: more formidable men should still be more supportive of war. We test this hypothesis in four countries: Argentina, Denmark, Israel, and Romania. In three, physically strong men (but not strong women) were significantly more supportive of military action. These findings support the hypothesis that modern warfare is influenced by a psychology designed for ancestral war.

Pride occurs in every known culture, appears early in development , is reliably triggered by achievements and formidability, and causes a characteristic display that is recognized everywhere. Here, we evaluate the theory that pride evolved to guide decisions relevant to pursuing actions that enhance valuation and respect for a person in the minds of others. By hypothesis, pride is a neurocomputational program tailored by selection to orchestrate cognition and behavior in the service of: (i) motivating the cost-effective pursuit of courses of action that would increase others' valuations and respect of the individual, (ii) motivating the advertisement of acts or characteristics whose recognition by others would lead them to enhance their evaluations of the individual, and (iii) mobilizing the individual to take advantage of the resulting enhanced social landscape. To modulate how much to invest in actions that might lead to enhanced evaluations by others, the pride system must forecast the magnitude of the evaluations the action would evoke in the audience and calibrate its activation proportionally. We tested this prediction in 16 countries across 4 continents (n = 2,085), for 25 acts and traits. As predicted, the pride intensity for a given act or trait closely tracks the valuations of audiences, local (mean r = +0.82) and foreign (mean r = +0.75). This relationship is specific to pride and does not generalize to other positive emotions that coactivate with pride but lack its audience-recalibrating function.

Pride occurs in every known culture, appears early in development , is reliably triggered by achievements and formidability, and causes a characteristic display that is recognized everywhere. Here, we evaluate the theory that pride evolved to guide decisions relevant to pursuing actions that enhance valuation and respect for a person in the minds of others. By hypothesis, pride is a neurocomputational program tailored by selection to orchestrate cognition and behavior in the service of: (i) motivating the cost-effective pursuit of courses of action that would increase others' valuations and respect of the individual, (ii) motivating the advertisement of acts or characteristics whose recognition by others would lead them to enhance their evaluations of the individual, and (iii) mobilizing the individual to take advantage of the resulting enhanced social landscape. To modulate how much to invest in actions that might lead to enhanced evaluations by others, the pride system must forecast the magnitude of the evaluations the action would evoke in the audience and calibrate its activation proportionally. We tested this prediction in 16 countries across 4 continents (n = 2,085), for 25 acts and traits. As predicted, the pride intensity for a given act or trait closely tracks the valuations of audiences, local (mean r = +0.82) and foreign (mean r = +0.75). This relationship is specific to pride and does not generalize to other positive emotions that coactivate with pride but lack its audience-recalibrating function. pride | valuation | decision-making | emotion | culture

According to the recalibrational theory of anger, anger is a computationally complex cognitive system that evolved to bargain for better treatment. Anger coordinates facial expressions, vocal changes, verbal arguments, the withholding of benefits, the deployment of aggression, and a suite of other cognitive and physiological variables in the service of leveraging bargaining position into better outcomes. The proto-typical trigger of anger is an indication that the offender places too little weight on the angry individual's welfare when making decisions, i.e. the offender has too low a welfare tradeoff ratio (WTR) toward the angry individual. Twenty-three experiments in six cultures, including a group of foragers in the Ecuadorian Amazon, tested six predictions about the computational structure of anger derived from the recalibrational theory. Subjects judged that anger would intensify when: (i) the cost was large, (ii) the benefit the offender received from imposing the cost was small, or (iii) the offender imposed the cost despite knowing that the angered individual was the person to be harmed. Additionally, anger-based arguments conformed to a conceptual grammar of anger, such that offenders were inclined to argue that they held a high WTR toward the victim, e.g., ''the cost I imposed on you was small " , ''the benefit I gained was large " , or ''I didn't know it was you I was harming. " These results replicated across all six tested cultures: the US, Australia, Turkey, Romania, India, and Shuar hunter-horticulturalists in Ecuador. Results contradict key predictions about anger based on equity theory and social constructivism.

Why do people support economic redistribution? Hypotheses include
inequity aversion, a moral sense that inequality is intrinsically
unfair, and cultural explanations such as exposure to and assimilation
of culturally transmitted ideologies. However, humans have
been interacting with worse-off and better-off individuals over
evolutionary time, and our motivational systems may have been
naturally selected to navigate the opportunities and challenges
posed by such recurrent interactions. We hypothesize that modern
redistribution is perceived as an ancestral scene involving three
notional players: the needy other, the better-off other, and the
actor herself. We explore how three motivational systems—compassion,
self-interest, and envy—guide responses to the needy
other and the better-off other, and how they pattern responses
to redistribution. Data from the United States, the United Kingdom,
India, and Israel support this model. Endorsement of redistribution
is independently predicted by dispositional compassion, dispositional
envy, and the expectation of personal gain from redistribution.
By contrast, a taste for fairness, in the sense of (i) universality
in the application of laws and standards, or (ii) low variance in
group-level payoffs, fails to predict attitudes about redistribution.