Publications

Working Paper
Howard RM, Spokes AC, Mehr SA, Krasnow MM. Welfare tradeoff psychology is present in children and adults. PsychArxiv. Working Paper. Publisher's Version
2022
Hilton CB, Moser CJ, Bertolo M, Lee-Rubin H, Amir D, Bainbridge CM, Simson J, Knox D, Glowacki L, Alemu E, et al. Acoustic regularities in infant-directed speech and song across cultures. Nature Human Behaviour. 2022. Publisher's VersionAbstract
When interacting with infants, humans often alter their speech and song in ways thought to support communication. Theories of human child-rearing, informed by data on vocal signalling across species, predict that such alterations should appear globally. Here, we show acoustic differences between infant-directed and adult-directed vocalizations across cultures. We collected 1,615 recordings of infant- and adult-directed speech and song produced by 410 people in 21 urban, rural and small-scale societies. Infant-directedness was reliably classified from acoustic features only, with acoustic profiles of infant-directedness differing across language and music but in consistent fashions. We then studied listener sensitivity to these acoustic features. We played the recordings to 51,065 people from 187 countries, recruited via an English-language website, who guessed whether each vocalization was infant-directed. Their intuitions were more accurate than chance, predictable in part by common sets of acoustic features and robust to the effects of linguistic relatedness between vocalizer and listener. These findings inform hypotheses of the psychological functions and evolution of human communication.
hilton_et_al-2022-nature_human_behaviour.pdf
Eisenbruch, Krasnow MM. Why warmth matters more than competence: A new evolutionary approach. Perspectives on Psychological Science. 2022. Publisher's Version eisenbruch_krasnow_2022_pops.pdf
2021
Mehr SA, Krasnow MM, Bryant GA, Hagen EH. Origins of music in credible signaling. Behavioral and Brain Sciences. 2021;44 :e60. Publisher's Version origins-of-music-in-credible-signaling.pdf
Young NR, Rosa ML, Mehr SA, Krasnow MM. Does greater morning sickness predict carrying a girl? Analysis of nausea and vomiting during pregnancy from retrospective report. Archives of Gynecology and Obstetrics. 2021;303 (5) :1161-1166. Publisher's Version young2020_article_doesgreatermorningsicknesspred.pdf
2019
Moser CJ, Lee-Rubin H, Collaboration I-DV, Bainbridge CM, Atwood S, Krasnow MM, Mehr SA. Acoustical regularities in infant-directed vocalizations worldwide. The Journal of the Acoustical Society of America. 2019;145 (3) :1766-1766. Publisher's Version
Mehr SA, Singh M, Knox D, Ketter DM, Pickens-Jones D, Atwood S, Lucas C, Jacobi N, Egner AA, Hopkins EJ, et al. Universality and diversity in human song. Science. 2019;366. Publisher's Version mehr_et_al_2019_science.pdf
Kotler J, Mehr SA, Egner A, Haig D, Krasnow MM. Response to music in Angelman syndrome contrasts with Prader-Willi syndrome. Evolution & Human Behavior. 2019;40 :420-426. Publisher's Version kotler_et_al_ehb_2019.pdf
2018
Mehr SA, Singh M, York H, Glowacki L, Krasnow MM. Form and function in human song. Current Biology. 2018;28 (3) :356-368. mehr_et_al_2018_cb.pdf
2017
Krasnow MM, Truxaw DR. The Adaptationist Program. In: In T. K. Shackelford & V. A. Weekes-Shackelford (Eds.) Encyclopedia of Evolutionary Psychological Science. Sage ; 2017.
Krasnow MM. An evolutionarily informed study of moral psychology. In: B. Voyer & T. Tarantola (Eds.) Moral Psychology: A Multidisciplinary Guide. USA: Springer ; 2017. krasnow_2017_an_evolutionarily_informed_study_of_moral_psychology.pdf
Delton AW, Krasnow MM. The psychology of deterrence explains why group membership matters for third-party punishment. Evolution & Human Behavior. 2017;38 (6) :734-743.Abstract

Humans regularly intervene in others’ conflicts as third-parties. This has been studied using the third-party punishment game: A third-party can pay a cost to punish another player (the “dictator”) who treated someone else poorly. Because the game is anonymous and one-shot, punishers are thought to have no strategic reasons to intervene. Nonetheless, punishers often punish dictators who treat others poorly. This result is central to a controversy over human social evolution: Did third-party punishment evolve to maintain group norms or to deter others from acting against one’s interests? This paper provides a critical test. We manipulate the ingroup/outgroup composition of the players while simultaneously measuring the inferences punishers make about how the dictator would treat them personally. The group norm predictions were falsified, as outgroup defectors were punished most harshly, not ingroup defectors (as predicted by ingroup fairness norms) and not outgroup members generally (as predicted by norms of parochialism). The deterrence predictions were validated: Punishers punished the most when they inferred that they would be treated the worst by dictators, especially when better treatment would be expected given ingroup/outgroup composition.

pagination_ens_6141.pdf
Mehr SA, Kotler J, Howard RM, Haig D, Krasnow MM. Genomic imprinting is implicated in the psychology of music. Psychological Science. 2017;28 (10) :1455-1467. mehr_et_al_2017_psci.pdf
Mehr SA, Krasnow MM. Parent-offspring conflict and the evolution of infant directed song. Evolution and Human Behavior. 2017. mehr_krasnow_2017_ehb.pdf
2016
Krasnow MM. Ultrasociality without group selection: Possible, reasonable, and likely. Behavioral and Brain Sciences. 2016;39 :e104. krasnow_2016 (comment on Gowdy & Krall).pdf
Krasnow MM, Delton AW. The sketch is blank: No evidence for an explanatory role for cultural group selection. Behavioral and Brain Sciences. 2016;39 :43-44. PDF
Krasnow MM, Delton AW. Are humans too generous and too punitive? Using psychological principles to further debates about human social evolution. Frontiers in Psychology. 2016. Publisher's VersionAbstract

Are humans too generous and too punitive? Many researchers have concluded that classic theories of social evolution (e.g., direct reciprocity, reputation) are not sufficient to explain human cooperation; instead, group selection theories are needed. We think such a move is premature. The leap to these models has been made by moving directly from thinking about selection pressures to predicting patterns of behavior and ignoring the intervening layer of evolved psychology that must mediate this connection. In real world environments, information processing is a non-trivial problem and details of the ecology can dramatically constrain potential solutions, often enabling particular heuristics to be efficient and effective. We argue that making the intervening layer of psychology explicit resolves decades-old mysteries in the evolution of cooperation and punishment.

Krasnow MM, Delton AW, Cosmides L, Tooby J. Looking Under the Hood of Third-Party Punishment Reveals Design for Personal Benefit. Psychological Science. 2016. psychological_science-2016-krasnow-0956797615624469.pdf
2015
Krasnow MM, Delton AW, Cosmides L, Tooby J. Group cooperation without group selection: Modest punishment can recruit much cooperation. PLoS One. 2015;10 (4) :e0124561. Web VersionAbstract

Humans everywhere cooperate in groups to achieve benefits not attainable by individuals. Individual effort is often not automatically tied to a proportionate share of group benefits. This decoupling allows for free-riding, a strategy that (absent countermeasures) outcompetes cooperation. Empirically and formally, punishment potentially solves the evolutionary puzzle of group cooperation. Nevertheless, standard analyses appear to show that punishment alone is insufficient, because second-order free riders (those who cooperate but do not punish) can be shown to outcompete punishers. Consequently, many have concluded that other processes, such as cultural or genetic group selection, are required. Here, we present a series of agent-based simulations that show that group cooperation sustained by punishment easily evolves by individual selection when you introduce into standard models more biologically plausible assumptions about the social ecology and psychology of ancestral humans. We relax three unrealistic assumptions of past models. First, past models assume all punishers must punish every act of free riding in their group. We instead allow punishment to be probabilistic, meaning punishers can evolve to only punish some free riders some of the time. This drastically lowers the cost of punishment as group size increases. Second, most models unrealistically do not allow punishment to recruit labor; punishment merely reduces the punished agent’s fitness. We instead realistically allow punished free riders to cooperate in the future to avoid punishment. Third, past models usually restrict agents to interact in a single group their entire lives. We instead introduce realistic social ecologies in which agents participate in multiple, partially overlapping groups. Because of this, punitive tendencies are more expressed and therefore more exposed to natural selection. These three moves toward greater model realism reveal that punishment and cooperation easily evolve by direct selection—even in sizeable groups. 

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