Looking for love

Kevin Lewis

February 02, 2013

Environment contingent preferences: Exposure to visual cues of direct male-male competition and wealth increase women's preferences for masculinity in male faces

Anthony Little, Lisa DeBruine & Benedict Jones
Evolution and Human Behavior, forthcoming

Previous studies show that parasite prevalence and mortality/health are related to cultural variation in women's preferences for attractive and masculine traits in men. Other studies have suggested that both male-male competition and wealth may also be important correlates of cross-cultural variation in women's masculinity preferences. Here we examined whether exposure to cues of direct male-male competition, violence, or wealth influenced women's face preferences. We showed women slideshows of images with cues of low and high direct male-male competition/violence or wealth and measured their visual preferences for masculine face traits. Recent visual experience changed women's preferences for facial masculinity, with women preferring more masculine male faces after exposure to images of men engaged in direct physical competition, images of weapons, or images depicting items of high monetary value. Recent visual experience had no significant effects on preferences for masculinity in same-sex faces. Given that high levels of direct physical competition and violence among males may increase the importance of direct intra-sexual competition, it may be adaptive for women to shift visual preferences in favor of males with face cues indicating physical strength and dominance over investment in such environments. Similarly, in wealthy environments investment may be less important than other aspects of quality and so it may be adaptive for women to shift visual preferences in favor of males with face cues indicating other aspects of quality over investment. Overall, our data demonstrate that preferences can be strategically flexible according to recent visual experience and support the notion of environment contingent preferences.


The Long-run Effect of Abortion on Sexually Transmitted Infections

Christopher Cornwell & Scott Cunningham
American Law and Economics Review, forthcoming

There is a growing literature on the effects of abortion legalization on a range of fertility outcomes. The now-famous paper by Donohue and Levitt [2001. "The Impact of Legalized Abortion on Crime," 116 Quarterly Journal of Economics 379-420], linking abortion to the decline in crime in the 1990s, has shifted the focus to non-fertility outcomes. We focus on STIs, specifically gonorrhea, exploiting the states that legalized abortion prior to Roe v. Wade as a quasi-experiment. Using data from the CDC, we present difference-in-difference estimates showing gonorrhea incidence fell among 15-19-year-olds in early-repeal states 15-19 years after legalization. The effects are most pronounced and precisely estimated for Black women. The basic findings hold up under triple-differencing with an untreated older cohort that was not in utero during abortion repeal.


Risk taking and Women's Menstrual Cycle: Near Ovulation, Women Avoid a Doubtful Man

Nicolas Guéguen
Letters on Evolutionary Behavioral Science, Spring 2012

Studies using surveys in which risk taking behaviors were measured show a decrease in risk taking during the ovulatory phase of the women's menstrual cycle. In this study, the distance between a woman and a shady confederate was measured in a waiting room. Then, a LH test was done in order to measure the participant's fertility risk. Results showed that near ovulation, participants sat further away from the confederate, revealing that women in their fertile phase displayed behavior to decrease the risk of sexual assault.


Men behaving nicely: Public goods as peacock tails

Mark Van Vugt & Wendy Iredale
British Journal of Psychology, February 2013, Pages 3-13

Insights from sexual selection and costly signalling theory suggest that competition for females underlies men's public good contributions. We conducted two public good experiments to test this hypothesis. First, we found that men contributed more in the presence of an opposite sex audience, but there was no parallel effect for the women. In addition, men's public good contributions went up as they rated the female observer more attractive. In the second experiment, all male groups played a five round public good game and their contributions significantly increased over time with a female audience only. In this condition men also volunteered more time for various charitable causes. These findings support the idea that men compete with each other by creating public goods to impress women. Thus, a public good is the human equivalent of a peacock's tail.


Are Human Mating Preferences with Respect to Height Reflected in Actual Pairings?

Gert Stulp et al.
PLoS ONE, January 2013

Pair formation, acquiring a mate to form a reproductive unit, is a complex process. Mating preferences are a step in this process. However, due to constraining factors such as availability of mates, rival competition, and mutual mate choice, preferred characteristics may not be realised in the actual partner. People value height in their partner and we investigated to what extent preferences for height are realised in actual couples. We used data from the Millennium Cohort Study (UK) and compared the distribution of height difference in actual couples to simulations of random mating to test how established mate preferences map on to actual mating patterns. In line with mate preferences, we found evidence for: (i) assortative mating (r = .18), (ii) the male-taller norm, and, for the first time, (iii) for the male-not-too-tall norm. Couples where the male partner was shorter, or over 25 cm taller than the female partner, occurred at lower frequency in actual couples than expected by chance, but the magnitude of these effects was modest. We also investigated another preference rule, namely that short women (and tall men) prefer large height differences with their partner, whereas tall women (and short men) prefer small height differences. These patterns were also observed in our population, although the strengths of these associations were weaker than previously reported strength of preferences. We conclude that while preferences for partner height generally translate into actual pairing, they do so only modestly.


Childhood Behavior Problems and Adolescent Sexual Risk Behavior: Familial Confounding in the Child and Adolescent Twin Study in Sweden (CATSS)

Kelly Donahue et al.
Journal of Adolescent Health, forthcoming

Objective: Previous studies have found associations between childhood behavior problems and adolescent sexual risk behavior. Using a quasi-experimental approach, we examined the extent to which this association may be due to between-family differences (i.e., unmeasured familial confounds) not adequately explored in prior research.

Methods: We used data from a longitudinal, population-based cohort of young twins in Sweden (first assessment: age 9 or 12 years; second assessment: age 15; n = 2,388). We explored the nature of the association between symptom scores for attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and conduct disorder (CD) at age 9 or 12 and the likelihood of having had sexual intercourse and number of sexual partners by age 15. Two-level mixed-effects models were used to estimate the effect of symptom score on each outcome after controlling for potential unmeasured familial confounds.

Results: Higher ADHD, ODD, and CD scores were associated with significantly increased likelihood of sexual intercourse by age 15. Higher ADHD and ODD scores were also associated with increased number of sexual partners. After controlling for unmeasured familial confounds, however, behavior problems were no longer significantly associated with either outcome.

Conclusion: The association between childhood behavior problems and sexual risk behaviors may be due to characteristics shared within families. Hence, prevention strategies aimed at reducing these behaviors might need to address broader risk factors that contribute to both behavior problems and a greater likelihood of sexual risk behavior.


Virtually Naked: Virtual Environment Reveals Sex-Dependent Nature of Skin Disclosure

Anna Lomanowska & Matthieu Guitton
PLoS ONE, January 2013

The human tendency to reveal or cover naked skin reflects a competition between the individual propensity for social interactions related to sexual appeal and interpersonal touch versus climatic, environmental, physical, and cultural constraints. However, due to the ubiquitous nature of these constraints, isolating on a large scale the spontaneous human tendency to reveal naked skin has remained impossible. Using the online 3-dimensional virtual world of Second Life, we examined spontaneous human skin-covering behavior unhindered by real-world climatic, environmental, and physical variables. Analysis of hundreds of avatars revealed that virtual females disclose substantially more naked skin than virtual males. This phenomenon was not related to avatar hypersexualization as evaluated by measurement of sexually dimorphic body proportions. Furthermore, analysis of skin-covering behavior of a population of culturally homogeneous avatars indicated that the propensity of female avatars to reveal naked skin persisted despite explicit cultural norms promoting less revealing attire. These findings have implications for further understanding how sex-specific aspects of skin disclosure influence human social interactions in both virtual and real settings.


The Association Between Sequences of Sexual Initiation and the Likelihood of Teenage Pregnancy

Bianka Reese et al.
Journal of Adolescent Health, February 2013, Pages 228-233

Purpose: Few studies have examined the health and developmental consequences, including unintended pregnancy, of different sexual behavior initiation sequences. Some work suggests that engaging in oral-genital sex first may slow the transition to coital activity and lead to more consistent contraception among adolescents.

Methods: Using logistic regression analysis, we investigated the association between sequences of sexual initiation (i.e., initiating oral-genital or vaginal sex first based on reported age of first experience) and the likelihood of subsequent teenage pregnancy among 6,069 female respondents who reported vaginal sex before age 20 years and participated in waves I and IV of the National Longitudinal Study of Adolescent Health.

Results: Among female respondents initiating vaginal sex first, 31.4% reported a teen pregnancy. Among female respondents initiating two behaviors at the same age, 20.5% reported a teen pregnancy. Among female respondents initiating oral-genital sex first, 7.9% reported a teen pregnancy. In multivariate models, initiating oral-genital sex first, with a delay of at least 1 year to vaginal sex, and initiating two behaviors within the same year were each associated with a lower likelihood of adolescent pregnancy relative to teens who initiated vaginal sex first (odds ratio = .23, 95% confidence interval: .15-.37; and odds ratio = .78, 95% confidence interval: .60-.92, respectively).

Conclusions: How adolescents begin their sexual lives may be differentially related to positive and negative health outcomes. To develop effective pregnancy prevention efforts for teens and ensure programs are relevant to youths' needs, it is important to consider multiple facets of sexual initiation and their implications for adolescent sexual health and fertility.


Hot or not: Response inhibition reduces the hedonic value and motivational incentive of sexual stimuli

Anne Ferrey, Alexandra Frischen & Mark Fenske
Frontiers in Psychology, December 2012

The motivational incentive of reward-related stimuli can become so salient that it drives behavior at the cost of other needs. Here we show that response inhibition applied during a Go/No-go task not only impacts hedonic evaluations but also reduces the behavioral incentive of motivationally relevant stimuli. We first examined the impact of response inhibition on the hedonic value of sex stimuli associated with strong behavioral-approach responses (Experiment 1). Sexually appealing and non-appealing images were both rated as less attractive when previously encountered as No-go (inhibited) than as Go (non-inhibited) items. We then discovered that inhibition reduces the motivational incentive of sexual appealing stimuli (Experiment 2). Prior Go/No-go status affected the number of key-presses by heterosexual males to view erotic-female (sexually appealing) but not erotic-male or scrambled-control (non-appealing) images. These findings may provide a foundation for developing inhibition-based interventions to reduce the hedonic value and motivational incentive of stimuli associated with disorders of self-control.


The Relationship Between Oral Contraceptive Use and Sensitivity to Olfactory Stimuli

Katy Renfro & Heather Hoffmann
Hormones and Behavior, forthcoming

The present study examined differences in olfactory sensitivity between 16 naturally cycling (NC) women and 17 women taking monophasic oral contraceptives (OCs) to six odors: lemon, peppermint, rose, musk, androstenone and androsterone. Thresholds were assessed twice for both groups of women (during the periovulatory and luteal phases of their cycles) via a forced-choice discrimination task. NC women in the periovulatory phase were significantly more sensitive to androstenone, androsterone, and musk than women taking OCs. These findings give support to odor-specific hormonal modulation of olfaction. Further, due to the social and possibly sexual nature of these odors, future work should address whether there is a relationship between decreased sensitivity to these odors and reported behavioral side effects among women taking OCs.


Major histocompatibility complex peptide ligands as olfactory cues in human body odour assessment

Manfred Milinski et al.
Proceedings of the Royal Society: Biological Sciences, 22 March 2013

In many animal species, social communication and mate choice are influenced by cues encoded by the major histocompatibility complex (MHC). The mechanism by which the MHC influences sexual selection is a matter of intense debate. In mice, peptide ligands of MHC molecules activate subsets of vomeronasal and olfactory sensory neurons and influence social memory formation; in sticklebacks, such peptides predictably modify the outcome of mate choice. Here, we examine whether this evolutionarily conserved mechanism of interindividual communication extends to humans. In psychometric tests, volunteers recognized the supplementation of their body odour by MHC peptides and preferred ‘self' to ‘non-self' ligands when asked to decide whether the modified odour smelled ‘like themselves' or ‘like their favourite perfume'. Functional magnetic resonance imaging indicated that ‘self'-peptides specifically activated a region in the right middle frontal cortex. Our results suggest that despite the absence of a vomeronasal organ, humans have the ability to detect and evaluate MHC peptides in body odour. This may provide a basis for the sensory evaluation of potential partners during human mate choice.


Guitar increases male Facebook attractiveness: Preliminary support for the sexual selection theory of music

Sigal Tifferet, Ofir Gaziel & Yoav Baram
Letters on Evolutionary Behavioral Science, Spring 2012

Music is a universal phenomenon that has genetic and brain-localized features. As such, it warrants adaptive evolutionary explanations. While some scholars believe that music arose as a by-product of other adaptations, others argue that music is likely to have served some adaptive function, for example in coalition signaling or mother-child bonding. The sexual selection theory of music suggests that music serves as a signal in mate selection. While this claim is prevalent, it lacks empirical evidence. A Facebook experiment revealed that women replied more positively to friendship requests from a man shown in a photo holding a guitar. These results offer initial support for the sexual selection theory of music.

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