Some Evolution and Human Behavior abstracts/excerpts


Consanguineous marriages: do genetic benefits outweigh its costs in populations with α+-thalassemia, hemoglobin S, and malaria?

Srdjan Denic et al.

Consanguinity is widespread in populations with endemic malaria. This practice, leading to an increase of homozygosis, could be either detrimental for lethal alleles (like hemoglobin S) or be potentially advantageous for beneficial alleles (like α+-thalassemia). The objective of this study was to analyze the effects of inbreeding on the fitness of a population with both, α+-thalassemia and hemoglobin S mutations. We calculated the relative fitness of an inbred population with α+-thalassemia and sickle cell anemia using a standard formula, and then compared it to that of an outbred population. An increase in the frequency of α+-thalassemia allele (0–1) results in a gain of relative fitness that is proportional to the coefficient of inbreeding; it is maximal at an allele frequency in the vicinity of 0.5. For hemoglobin S, an increase of frequency (0 to equilibrium point) produces a progressive loss of relative fitness that is also proportional to the coefficient of inbreeding; it is lowest at the equilibrium frequency that is always lower than 0.5. In a consanguineous population with both α+-thalassemia and hemoglobin S under selection pressure of malaria, the sum of contrary effects of inbreeding on the relative fitness of population depends on the frequencies of the two alleles and the coefficient of inbreeding.

Keywords: Consanguineous marriages; Inbreeding; Malaria; Thalassemia; Hemoglobin S; Relative fitness; Simulation model

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Our findings provide a plausible hypothesis for explaining the confinement of consanguineous marriages to the tropical and subtropical regions where malaria is endemic and explain their absence in other parts of the World. As such, they complement the socioeconomic benefits theory of consanguinity ([Alwan and Modell, 1997], [Bittles, 2001] and [Khlat, 1997]). If consanguinity produces more surviving offspring (higher fitness) in some malarious populations, then a better protection of these survivors of malaria, as per socioeconomic theory of consanguinity, would further add to family fitness. Although neither theory is experimentally testable, the theoretical arguments underpinning both, as well as their complementing picture, will further insight into the causes and effects of customs regarding human reproduction.


Correlated preferences for men's facial and vocal masculinity

David R. Feinberga et al.

Previous studies have reported variation in women's preferences for masculinity in men's faces and voices. Women show consistent preferences for vocal masculinity, but highly variable preferences for facial masculinity. Within individuals, men with attractive voices tend to have attractive faces, suggesting common information may be conveyed by these cues. Here we tested whether men and women with particularly strong preferences for male vocal masculinity also have stronger preferences for male facial masculinity. We found that masculinity preferences were positively correlated across modalities. We also investigated potential influences on these relationships between face and voice preferences. Women using oral contraceptives showed weaker facial and vocal masculinity preferences and weaker associations between masculinity preferences across modalities than women not using oral contraceptives. Collectively, these results suggest that men's faces and voices may reveal common information about the masculinity of the sender, and that these multiple quality cues could be used in conjunction by the perceiver in order to determine the overall quality of individuals.

Keywords: Face; Voice; Femininity; Hormonal contraceptive; Birth control; Pill


Why do some dads get more involved than others? Evidence from a large British cohort

Daniel Nettle

Previous studies in developed-world populations have found that fathers become more involved with their sons than with their daughters and become more involved with their children if they are of high socioeconomic status (SES) than if they are of low SES. This paper addresses the idea proposed by Kaplan et al. that this pattern arises because high-SES fathers and fathers of sons can make more difference to offspring outcomes. Using a large longitudinal British dataset, I show that paternal involvement in childhood has positive associations with offspring IQ at age 11, and offspring social mobility by age 42, though not with numbers of grandchildren. For IQ, there is an interaction between father's SES and his level of involvement, with high-SES fathers making more difference to the child's IQ by their investment than low-SES fathers do. The effects of paternal investment on the IQ and social mobility of sons and daughters were the same. Results are discussed with regard to the evolved psychology and social patterning of paternal behaviour in humans.

Keywords: Fathers; Sons; Daughters; Socioeconomic status

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As several previous studies in developed societies have also found ([Cabrera et al., 2000], [Harris et al., 1998], [Kaplan et al., 1998] and [Lawson & Mace, submitted for publication]), paternal involvement is patterned by SES and by sex of the child, with high-SES fathers more involved than low-SES ones, and sons receiving more paternal involvement than daughters. High paternal involvement is associated with significantly increased IQ scores at age 11 in this large British cohort, even when family SES and number of other siblings are controlled for. This result is consistent with previous findings for IQ and educational attainment measures from this (Flouri & Buchanan, 2004 E. Flouri and A. Buchanan, Early father's and mother's involvement and child's later educational outcomes, British Journal of Educational Psychology 74 (2004), pp. 141–153. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (17)Flouri & Buchanan, 2004) and other (Kaplan et al., 1998) cohorts.

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This study shows for the first time an interaction effect with father's SES, with professional and managerial fathers making more difference to child IQ scores when they invest than unskilled fathers do (see Fig. 3). High-SES fathers may have more skills to enrich and improve the environment of the child's development than low-SES fathers do. As Kaplan et al. (1998) suggested might be the case, high SES fathers seem to be more efficient at embodying human capital in their children than low-SES fathers are. This gives a powerful potential explanation of why low-SES groups are characterised by low paternal effort. The returns to effort are low, and therefore men have no incentive for higher effort.

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High-investing fathers did not have more grandchildren than low-investing fathers in this cohort. This does not necessarily mean that investment is not adaptive, since evolution favours strategies that maximise the contribution of the lineage to the population at an indefinitely far point in the future, and strategies can be adaptive even if their mean payoffs do not exceed the average for several generations (McNamara & Houston, 2006). High-investing fathers, especially from high SES backgrounds, did improve the quality and final social status of their children, and given that social status generally predicts marriage and fertility, at least for men (Fieder & Huber, 2007), it is quite plausible that they thereby reduce the risk of lineage extinction in the longer term. On the other hand, it may be that in this low-fertility, high parental investment, post demographic transition society, investment strategies that might have had an adaptive basis in ancestral environments have become decoupled from realised (grand)offspring numbers.


Sexual coercion and life-history strategy

Paul R. Gladden

The present study evaluates three ultimate theories accounting for individual differences in sexually coercive tendencies: (1) Life History (LH) theory, (2) Competitively Disadvantaged Male theory, and (3) Sexual Coercion as a By-product theory. Three-hundred twenty-four college students completed questionnaires measuring LH strategy, perceived mate value, mating effort, short-term and long-term mating orientation, aggressive tendencies, psychopathy, and sexually coercive behavior. Eight tactical subscales extracted from the Sexual Acts and Perceptions Inventory converged upon one latent Sexual Coercion factor. The predictor variables clustered into a second Protective LH latent factor, which buffered Sexual Coercion. The Protective LH factor fully mediated the relation between sex and Sexual Coercion. Thus, the three evolutionary accounts of sexual coercion describe unique facets of a single LH trait rather than three dissociable alternatives. We discuss the conclusion that reproductive LH strategy partially underlies the variation in predisposition toward sexual coercion.

Keywords: Sexual coercion; Life-history theory; Sex differences; Social deviance; Aggression

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4.1. LH strategy and social deviance

Ellis (1988) and others (e.g., Rushton, 1985) argue that a fast LH strategy underlies general criminality. Consistent with this view, we found that the short form of the Arizona LH Battery converged on the Protective LH factor with measures of socially deviant attitudes (e.g., aggression, psychopathy, machiavellianism), which served as inverse indicators of that factor. As noted above, LH strategies are composed of coordinated tactics. Our findings suggest that if men possess evolved specialized adaptations for sexual coercion, then sexual coercion may be one tactic among many subsumed by a general fast LH strategy, that is, a suite of tactics characterized by a diverse repertoire of socially deviant adaptive tactics. For example, if general social deviance is driven by fast LH strategies (e.g., [Ellis, 1988] and [Figueredo et al., 2006]), then sexually coercive individuals could be “criminal-generalists” (Malamuth et al., 2005 N. Malamuth, M. Huppin and B. Paul, Sexual coercion, The handbook of evolutionary psychology (2005), pp. 394–418.Malamuth et al., 2005), yet also be specialized to use sexual coercion as one of the tactics characteristic of their fast reproductive strategies. In short, sexual coercion could be one specialized adaptive tactic that contributed to the reproductive success of fast LH individuals in certain social contexts. One possibility is that fast LH strategies develop partly in response to self-assessments of low mate value and that these strategies are specialized for sexual coercion. Alternatively, sexual coercion may not have directly contributed to reproductive success but instead might be generated as a side effect of selection for fast LH traits that were under direct selective pressure such as interest in casual sex and risk-taking ([Palmer, 1991], [Symons, 1979] and [Thornhill and Palmer, 2000]).

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To summarize, slow LH strategy, mate value, low mating-effort, a long-term sexual strategy, low psychopathy, low machiavellianism, and low aggression clustered into one common Protective LH factor that was negatively associated with a Sexual Coercion factor. The Protective LH factor fully mediated the relation between subject sex and Sexual Coercion. Therefore, Protective LH predictors co-occurred within individuals, indicating a single underlying construct that buffers individuals against using sexually coercive tactics. The LH view is consistent with either the idea that sexual coercion is a specific adaptation or that it is a by-product of traits adaptive for fast LH individuals ([Palmer, 1991], Thornhill and Palmer, 2000 R. Thornhill and C. Palmer, A natural history of rape: Biological bases of sexual coercion, MIT Press, Cambridge, MA (2000).[Thornhill and Palmer, 2000], [Thornhill and Palmer, 2004] and [Thornhill and Thornhill, 1992]). The Protective LH factor found in the present study must be replicated in other samples to support or refute the view that the three seemingly alternative evolutionary accounts describe different features of fast LH individuals.

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