Does morality have a biological basis? An empirical test of the factors governing moral sentiments relating to incest

Abstract

Kin-recognition systems have been hypothesized to exist in humans, and adaptively to regulate altruism and incest avoidance among close genetic kin. This latter function allows the architecture of the kin recognition system to be mapped by quantitatively matching individual variation in opposition to incest to individual variation in developmental parameters, such as family structure and co-residence patterns. Methodological difficulties that appear when subjects are asked to disclose incestuous inclinations can be circumvented by measuring their opposition to incest in third parties, i.e. morality. This method allows a direct test of Westermarck's original hypothesis that childhood co-residence with an opposite-sex individual predicts the strength of moral sentiments regarding third-party sibling incest. Results support Westermarck's hypothesis and the model of kin recognition that it implies. Co-residence duration objectively predicts genetic relatedness, making it a reliable cue to kinship. Co-residence duration predicts the strength of opposition to incest, even after controlling for relatedness and even when co-residing individuals are genetically unrelated. This undercuts kin-recognition models requiring matching to self (through, for example, major histocompatibility complex or phenotypic markers). Subjects' beliefs about relatedness had no effect after controlling for co-residence, indicating that systems regulating kin-relevant behaviours are non-conscious, and calibrated by co-residence, not belief.

Kin Affiliation Across the Ovulatory Cycle

“…For instance, only recently have researchers started to investigate how people categorize other individuals according to genetic relatedness, an ability required for inbreeding avoidance (Lieberman, Tooby, & Cosmides, 2007). There is also relatively little known about how different contexts affect the undesirability of genetic relatives as sexual partners (e.g., Haig, 1999) and how personal sexual aversions might translate into cultural sanctions such as incest taboos (e.g., Fessler & Navarrete, 2004;Lieberman, Tooby, & Cosmides, 2003, 2007. Moreover, whereas there has recently been much work on shifts in the qualities women desire in mates near the time of ovulation (e.g., Gangestad & Thornhill, 2008;Pillsworth & Haselton, 2006), this study suggests that there are corresponding shifts in psychological aversions designed to help women avoid reproductive costs when fertile.…”

Microbes, mating, and morality: Individual differences in three functional domains of disgust.

“…This theoretical framework has proven useful in a variety of research areas, including mate choice (Bleske-Reshek & Buss, 2006;Gangestad, Garver-Apgar, Simpson, & Cousins, 2007), aggression (Griskevicius, Tybur, Gangestad, Perea, Shapiro, & Kenrick, in press), person perception (Becker, Kenrick, Neuberg, Blackwell, & Smith, 2007;Cottrell, Neuberg, & Li, 2007), kin-directed behaviors such as altruism and sexual avoidance (Ackerman, Kenrick, & Schaller, 2007;Burnstein, Crandall, & Kitayama, 1994;Lieberman, Tooby, & Cosmides, 2003, perceptual biases (Haselton & Funder, 2006;Maner et al, 2005), social stigma (Kurzban & Leary, 2001; Three domains of disgust 9…”

Evitação e proibição do incesto: fatores psicobiológicos e culturais

“…As Lieberman, Tooby and Cosmides (2003) have emphasized, the evolution of the kinship recognition system depends on the selection of tracks that: (1) provide probabilistic information that certainly predicts the kinship; (2) have been stable throughout generations midst the adaptations and (3) could be sufficiently detected at low cost. In this study, the authors have made a survey of 186 Californian students, and asked the participants to set 19 acts in order, from the less to the most morally wrong; consensual sexual intercourse and marriage between siblings of opposite gender have been included in this list.…”

“…There was negligence to psychobiological and evolutionary explanations for the incest prohibition and rejection, that is, the cognitive human architecture probably has a circuit that evolves because prohibits the sexual activity between individuals with genetic kinship and the incest institutional regulation does not occur exclusively by sociocultural channel (Lieberman, Tooby, & Cosmides, 2003.…”