Evolutionary psychology of altruism and mate choice

This category contains 4 posts

Men do not have a stronger preference than women for self-resemblant child faces

Paola Bressan, Marco Bertamini, Alessandra Nalli, Arianna Zanutto

Are men more likely than women to take into account a child’s facial resemblance to themselves when making hypothetical parental investment choices? The benefits of self-resemblance in decreasing relatedness uncertainty are larger in men than in women for direct descendants. However, they are identical in men and women for collateral relatives, such as siblings, cousins, nephews, and nieces; these individuals can also be the recipients of parental-like altruism, which comes primarily from women. Published data are contradictory. In the present study, 14 men and 14 women were shown child faces and asked to judge their attractiveness, adoptability, and familiarity. The faces had been digitally manipulated to resemble (at three different resemblance levels, two of which were under recognition threshold) either the experimental participant, an acquaintance, or strangers. We found a significant preference for self-resemblant children in women, but not in men. This was not an artefact of women being better at detecting self-resemblance, given that at the highest resemblance level more men than women recognized themselves. Overall, face preference increased with face familiarity; for self-resemblant faces, this correlation was not mediated by conscious self-recognition. We discuss how the fast-response, multiple-question procedure used in previous experiments may have led to reports of a much larger self-resemblance preference in men than in women.

Bressan, P., Bertamini, M., Nalli, A., & Zanutto, A. (2009). Men do not have a stronger preference than women for self-resemblant child faces. Archives of Sexual Behavior, 38, 657-664.

child morphs

These faces are morphs, containing 25%, 40%, and 50% of a female participant's traits.

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Human kin recognition is self- rather than family-referential

Paola Bressan, Guendalina Zucchi

Inclusive fitness theory predicts that organisms will tend to help close kin more than less related individuals. In a variety of birds and mammals, relatives are recognized by comparing their phenotype to an internal representation or template, which might be learned through either repeated exposure to family members or self-inspection. Mirrors are ubiquitous now, but were absent during our evolutionary history; hence it is hard to predict, and empirically unknown, whether human kin recognition is family- or self-referential. Here we put this issue to the strongest possible test by comparing nepotistic behaviour towards self- versus co-twin-resemblant individuals. Seventy monozygotic and dizygotic twins were shown same-sex faces, covertly manipulated to resemble either themselves or their co-twin, and indicated which individual they would prefer in two prosocial contexts. Self-resemblant faces were significantly preferred to twin-resemblant faces, showing that visual information about the self supersedes that about close family members in the kin-recognition template. Because, under conditions of paternal uncertainty, a reliable family-referent template could be based only on one’s mother and maternal relatives, a unique advantage of self-referent phenotype matching is the possibility of (consciously or unconsciously) identifying one’s father and paternal relatives as kin.

Bressan, P., & Zucchi, G. (2009). Human kin recognition is self- rather than family-referential. Biology Letters, 5, 336-338.

Two identical twins morphed with the female model

Because monozygotic twins are identical genetically, but not developmentally, morph pairs were very similar but never impossible to tell apart.

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• read coverage in the Telegraph (“We are friendlier to people who resemble us, scientists find”, 4 March 2009)
• read coverage in Focus (“Je ähnlicher, desto hilfsbereiter”, 4 March 2009)
• read coverage in Stern (“Gleich und gleich hilft sich gern”, 4 March 2009)
• read coverage in Wissenschaft (“Das eigene Gesicht als unbewusster Standard”, 4 March 2009)

Biologically costly altruism depends on emotional closeness among step but not half or full siblings

Paola Bressan, Stephen M. Colarelli, Mary Beth Cavalieri

We studied altruistic behaviors of varying biological cost (high, medium, and low) among siblings of varying genetic relatedness (full, half, and step). In agreement with inclusive fitness theory, the relative importance of either reliable (such as co-residence) or heuristic (such as emotional closeness) kinship cues depended crucially on the costs of help. When help did not endanger the altruist’s life, thus making reciprocation possible, emotional closeness was the strongest predictor of altruism; perceived physical and psychological similarity to the sibling amplified altruistic behavior via their association with emotional closeness. When help endangered the altruist’s life, thus making reciprocation unlikely, the strongest predictor of altruism was the ancestrally valid kinship cue of co-residence duration. Emotional closeness predicted costly altruism only for step siblings; its effects were non-significant when siblings were genetically related. Our findings support the idea that emotional closeness promotes costly altruistic behavior by serving as a surrogate kinship cue when more reliable cues are missing.

Bressan, P., Colarelli, S. M., & Cavalieri, M. B. (2009). Biologically costly altruism depends on emotional closeness among step but not half or full siblings. Evolutionary Psychology, 7, 118-132.

The best men are (not always) already taken: Female preference for single versus attached males depends on conception risk

Paola Bressan, Debora Stranieri

Because men of higher genetic quality tend to be poorer partners and parents than men of lower genetic quality, women may profit from securing a stable investment from the latter, while obtaining good genes via extrapair mating with the former. Only if conception occurs, however, do the evolutionary benefits of such a strategy overcome its costs. Accordingly, we predicted that (a) partnered women should prefer attached men, because such men are more likely than single men to have pair-bonding qualities, and hence to be good replacement partners, and (b) this inclination should reverse when fertility rises, because attached men are less available for impromptu sex than single men. In this study, 208 women rated the attractiveness of men described as single or attached. As predicted, partnered women favored attached men at the low-fertility phases of the menstrual cycle, but preferred single men (if masculine, i.e., advertising good genetic quality) when conception risk was high.

Bressan, P., & Stranieri, D. (2008). The best men are (not always) already taken: Female preference for single versus attached males depends on conception risk. Psychological Science, 19, 145-151.


• read coverage in Nature (“Fertile wives find single men sexy”, 26 February 2008)