Findings

Conceivable Consequences

Kevin Lewis

December 25, 2009

Height among Women is Curvilinearly Related to Life History Strategy

Abraham Buunk, Thomas Pollet, Liga Klavina, Aurelio José Figueredo & Pieternel Dijkstra
Evolutionary Psychology, November 2009, Pages 545-559

Abstract:
It was hypothesized that women of medium height would show a more secure, long-term mating pattern characterized by less jealousy, less intrasexual competition and a "slower" life history strategy. In three samples of female undergraduate students clear support was found for these hypotheses. In Study 1, among 120 participants, height was curvilinearly related to well-established measures of possessive and reactive jealousy, with women of medium height being less jealous than tall as well as short women. In Study 2, among 40 participants, height was curvilinearly related to intrasexual competition, with women of medium height being less competitive towards other women than tall as well as short women. In Study 3, among 299 participants, height was curvilinearly related to the Mini-K, a well-validated measure of "slower" life history strategy, with women of medium height having a slower life history strategy than tall as well as short women. The results suggest that women of medium height tend to follow a different mating strategy than either tall or short women. Various explanations and implications of these results are discussed.

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Wartime sex ratios: Stress, male vulnerability and the interpretation of atypical sex ratio data

Valerie Grant
Journal of Evolutionary Psychology, December 2009, Pages 251-262

Abstract:
At the end of war, and other times of both chronic and acute stress, remarkable changes occur in the human secondary (birth) sex ratio. At the end of a long war, significantly more boys are born; after a short war, or disaster, fewer boys than usual are born six to nine months later. Since it is commonly held that the sex of the offspring is a matter of chance, these data provide an intriguing problem; but new findings in reproductive physiology, and an increased understanding of male vulnerability, could help resolve it. It appears the sex ratio of offspring may be influenced by variations in the mother's follicular testosterone. Under conditions of chronic stress, maternal testosterone rises, resulting in an increase in male conceptions; but these same stressful conditions also exacerbate differential male vulnerability, so more males are lost during pregnancy. At the end of war, improving conditions temper male vulnerability, leaving higher sex ratios at birth. Conversely, normal conditions at conception followed by a severe stressor during pregnancy result in lower secondary sex ratios.

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The Rise of Age Homogamy in 19th Century Western Europe

Bart Van de Putte, Frans Van Poppel, Sofie Vanassche, Maria Sanchez, Svetlana Jidkova, Mieke Eeckhaut, Michel Oris & Koen Matthijs
Journal of Marriage and Family, December 2009, Pages 1234-1253

Abstract:
In many parts of Western Europe the age at first marriage and the level of celibacy declined in the second half of the 19th century. This weakening of the European marriage pattern (EMP) can be interpreted as a "classic" response to the increase of the standard of living, but a more far-reaching interpretation is that the erosion of the EMP was part of a cultural shift characterized by the rise of a new, less instrumental and more egalitarian view on marriage and partner selection. The latter vision implies the increase of the preference for a same age marriage. We test this explanation by using a combined Belgian-Dutch data set of marriage certificates (N = 766,412). Our findings corroborate the "cultural shift thesis."

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On the Origin of Species by Natural and Sexual Selection

G. Sander van Doorn, Pim Edelaar & Franz Weissing
Science, 18 December 2009, Pages 1704-1707

Abstract:
Ecological speciation is considered an adaptive response to selection for local adaptation. However, besides suitable ecological conditions, the process requires assortative mating to protect the nascent species from homogenization by gene flow. By means of a simple model, we demonstrate that disruptive ecological selection favors the evolution of sexual preferences for ornaments that signal local adaptation. Such preferences induce assortative mating with respect to ecological characters and enhance the strength of disruptive selection. Natural and sexual selection thus work in concert to achieve local adaptation and reproductive isolation, even in the presence of substantial gene flow. The resulting speciation process ensues without the divergence of mating preferences, avoiding problems that have plagued previous models of speciation by sexual selection.

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The Short-Term Impacts of a Schooling Conditional Cash Transfer Program on the Sexual Behavior of Young Women

Sarah Baird, Ephraim Chirwa, Craig McIntosh & Berk Özler
World Bank Working Paper, October 2009

Abstract:
Recent evidence suggests that conditional cash transfer programs for schooling are effective in raising school enrollment and attendance. However, there is also reason to believe that such programs can affect other outcomes, such as the sexual behavior of their young beneficiaries. Zomba Cash Transfer Program is a randomized, ongoing conditional cash transfer intervention targeting young women in Malawi that provides incentives (in the form of school fees and cash transfers) to current schoolgirls and recent dropouts to stay in or return to school. An average offer of US$10/month conditional on satisfactory school attendance - plus direct payment of secondary school fees - led to significant declines in early marriage, teenage pregnancy, and self-reported sexual activity among program beneficiaries after just one year of program implementation. For program beneficiaries who were out of school at baseline, the probability of getting married and becoming pregnant declined by more than 40 percent and 30 percent, respectively. In addition, the incidence of the onset of sexual activity was 38 percent lower among all program beneficiaries than the control group. Overall, these results suggest that conditional cash transfer programs not only serve as useful tools for improving school attendance, but may also reduce sexual activity, teen pregnancy, and early marriage.

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The Impact of Living in Co-ed Resident Halls on Risk-taking Among College Students

Brian Willoughby & Jason Carroll
Journal of American College Health, November-December 2009, Pages 241-246

Objective: Although previous research has suggested that college housing impacts student behavior and outcomes, recent research linking college housing to risk-taking has been limited. In this study, we investigate if patterns of risk behavior differ based on the type of college housing environment students reside in.

Participants: This study utilizes 510 college students living in on-campus college housing. Methods: Students were recruited from 5 college sites across the United States. Participants responded to survey items online that measured current risk-taking behaviors such as binge drinking and sexual activity.

Results: After controlling for an assortment of demographic and psychological variables, results indicated that students living in co-ed housing were more likely than students living in gender-specific housing to binge drink and consume alcohol, have more permissive sexual attitudes, and have more recent sexual partners.

Conclusions: On-campus housing environments impact college student risk behaviors. Implications are discussed in light of the decline of in loco parentis on most college campuses.

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Birth order affects behaviour in the investment game: Firstborns are less trustful and reciprocate less

Alexandre Courtiol, Michel Raymond & Charlotte Faurie
Animal Behaviour, December 2009, Pages 1405-1411

Abstract:
Explaining the behavioural variations observed between individuals is an important step for understanding the evolution of human cooperation and personality traits. Birth order is a potentially important variable that implies physical and cognitive differences between siblings and differential access to parental resources during childhood. These differences have been shown to influence several personality characteristics in adulthood. We tested the hypothesis that birth order can shape adult cooperative behaviours towards nonkin. An anonymous investment game was played by 510 unrelated students. The results of the game show that firstborns were less trustful and reciprocated less than others. No significant differences in trust or reciprocity were found among laterborn and only children based on birth order. Firstborn status was a better predictor of cooperativeness than age, sex, income or religion. These results constitute some of the first experimental evidence that birth order differences established within the family can persist in adult behaviour among nonkin. We discuss the implications of this finding for the evolution of human cooperation.

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Birth Weight in Relation to Leisure Time Physical Activity in Adolescence and Adulthood: Meta-Analysis of Results from 13 Nordic Cohorts

Lise Geisler Andersen, Lars Ängquist, Michael Gamborg, Liisa Byberg, Calle Bengtsson, Dexter Canoy, Johan Eriksson, Marit Eriksson, Marjo-Riitta Järvelin, Lauren Lissner, Tom Nilsen, Merete Osler, Kim Overvad, Finn Rasmussen, Minna Salonen, Lene Schack-Nielsen, Tuija Tammelin, Tomi-Pekka Tuomainen, Thorkild Sørensen & Jennifer Baker
PLoS ONE, December 2009, e8192

Background: Prenatal life exposures, potentially manifested as altered birth size, may influence the later risk of major chronic diseases through direct biologic effects on disease processes, but also by modifying adult behaviors such as physical activity that may influence later disease risk.

Methods/Principal Findings: We investigated the association between birth weight and leisure time physical activity (LTPA) in 43,482 adolescents and adults from 13 Nordic cohorts. Random effects meta-analyses were performed on categorical estimates from cohort-, age-, sex- and birth weight specific analyses. Birth weight showed a reverse U-shaped association with later LTPA; within the range of normal weight the association was negligible but weights below and above this range were associated with a lower probability of undertaking LTPA. Compared with the reference category (3.26-3.75 kg), the birth weight categories of 1.26-1.75, 1.76-2.25, 2.26-2.75, and 4.76-5.25 kg, had odds ratios of 0.67 (95% confidence interval: 0.47, 0.94), 0.72 (0.59, 0.88), 0.89 (0.79, 0.99), and 0.65 (0.50, 0.86), respectively. The shape and strength of the birth weight-LTPA association was virtually independent of sex, age, gestational age, educational level, concurrent body mass index, and smoking.

Conclusions/Significance: The association between birth weight and undertaking LTPA is very weak within the normal birth weight range, but both low and high birth weights are associated with a lower probability of undertaking LTPA, which hence may be a mediator between prenatal influences and later disease risk.

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The challenge of sexual attraction within heterosexuals' cross-sex friendship

Panayotis Halatsis & Nicolas Christakis
Journal of Social and Personal Relationships, September/November 2009, Pages 919-937

Abstract:
This study investigated whether sexual attraction constitutes a "challenge" in cross-sex friendship, as well as the role and consequences of sexual attraction in friendship development. We present data from two studies. Study I, using detailed interviews, found three patterns of sexual attraction management. Study II, using a questionnaire, assessed important issues from Study I. The findings support the view that sexual attraction is indeed a challenge for cross-sex friends. Nevertheless, when sexual attraction is expressed, the friendship prevails in the majority of the cases. The implications of these findings in understanding the role of sexual attraction in cross-sex friendships are discussed.

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The Relationship Between State Abortion Policies and Abortion Providers

Marshall Medoff
Gender Issues, December 2009, Pages 224-237

Abstract:
This study empirically examines whether restrictive state abortion laws have an impact on the number of abortion providers over the period 1982-2005. The empirical results find that medicaid funding restrictions, parental involvement laws and targeted regulation of abortion providers (TRAP laws) annual licensing fees significantly deter physicians or organizations from becoming or remaining abortion providers. The numerical impact of a Medicaid funding restriction, parental involvement law and a TRAP licensing fee is to reduce the number of abortion providers per 100,000 pregnancies by 12.8, 19.6 and 15.5, respectively, as compared to states without these restrictive abortion laws. The empirical results also show that parental notification laws have a significantly larger negative impact on the number of abortion providers than parental consent laws.


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