The evolution of a social construction: the case of male homosexuality

Male homosexuality has been viewed by evolutionary psychologists as a Darwinian paradox, and by other social scientists as a social construction. We argue that it is better understood as an evolutionary social construction. Male homosexuality as we now know it is an 18th-century invention, but nonexclusive same-sex sexual behavior has a long evolutionary history. According to the alliance-formation hypothesis, same-sex sexuality evolved by natural selection because it created or strengthened male-male alliances and allowed low-status males to reposition themselves in the group hierarchy and thereby increase their reproductive success. This hypothesis makes sense of some odd findings about male homosexuality and helps to explain the rise in exclusive male homosexuality in the 18th century. The sociohistorical conditions around 1700 may have resulted in an increase in same-sex sexual behavior. Cultural responses to same-sex sexuality led to the spread of exclusive homosexual behavior and to the creation of a homosexual identity. Understanding male homosexuality as an evolutionary social construction can help us move beyond the traditionally polarized debate between evolutionary psychologists and social constructionists.     

Quantitative and theoretical analyses of the relation between older brothers and homosexuality in men

Meta-analysis of aggregate data from 14 samples representing 10,143 male subjects shows that homosexuality in human males is predicted by higher numbers of older brothers, but not by higher numbers of older sisters, younger brothers, or younger sisters. The relation between number of older brothers and sexual orientation holds only for males. This phenomenon has therefore been called the fraternal birth order effect. Research on birth order, birth weight, and sexual orientation suggests that the developmental pathway to homosexuality initiated by older brothers operates during prenatal life. Calculations assuming a causal relation between older brothers and sexual orientation have estimated the proportion of homosexual men who owe their sexual orientation to fraternal birth order at 15% in one study and 29% in another. The maternal immune hypothesis proposes that the fraternal birth order effect reflects the progressive immunization of some mothers to male-specific antigens by each succeeding male fetus and the increasing effects of such immunization on sexual differentiation of the brain in each succeeding male fetus. There are at least three possible mechanisms by which the mother's immune response could influence the fetus: the transfer of anti-male antibodies across the placenta from the maternal into the fetal compartment, the transfer of maternal cytokines across the placenta, and maternal immune reactions affecting the placenta itself. This hypothesis is consistent with recent studies showing that the quantity of fetal cells that enter the maternal circulation is greater than previously thought, and that the number of male-specific proteins encoded by Y-chromosome genes is greater than previously thought.     

The female orgasm and the homology concept in evolutionary biology

The definition of homology and its application to reproductive structures, external genitalia, and the physiology of sexual pleasure has a tortuous history. While nowadays there is a consensus on the developmental homology of genital and reproductive systems, there is no agreement on the physiological translation, or the evolutionary origination and roles, of these structural correspondences and their divergent histories. This paper analyzes the impact of evolutionary perspectives on the homology concept as applied to the female orgasm, and their consequences for the biological and social understanding of female sexuality and reproduction. After a survey of the history of pre-evolutionary biomedical views on sexual difference and sexual pleasure, we examine how the concept of sexual homology was shaped in the new phylogenetic framework of the late 19th century. We then analyse the debates on the anatomical locus of female pleasure at the crossroads of theories of sexual evolution and new scientific discourses in psychoanalysis and sex studies. Moving back to evolutionary biology, we explore the consequences of neglecting homology in adaptive explanations of the female orgasm. The last two sections investigate the role played by different articulations of the homology concept in evolutionary developmental explanations of the origin and evolution of the female orgasm. These include the role of sexual, developmental homology in the byproduct hypothesis, and a more recent hypothesis where a phylogenetic, physiological concept of homology is used to account for the origination of the female orgasm. We conclude with a brief discussion on the social implications for the understanding of female pleasure derived from these different homology frameworks.     

The biology of human psychosexual differentiation

Most attempts to identify biological underpinnings of gender identity and sexual orientation in humans have investigated effects of sex steroids, so pivotal in the differentiation of the genitalia, showing strong parallels between animals and the human. The information on humans is derived from the so-called 'experiments of nature', clinical entities with a lesser-than-normal androgen exposure in XY subjects and a higher than normal androgen exposure in XX subjects. Prenatal androgenization appears to predispose to a male gender identity development, but apparently not decisively since 40-50% of 46,XY intersexed children with a history of prenatal androgen exposure do not develop a male gender identity. Obviously, male-to-female transsexuals, with a normal androgen exposure prenatally (there is no serious evidence to the contrary) develop a female gender identity, through unknown biological mechanisms apparently overriding the effects of prenatal androgens. The latest studies in 46, XX subjects exposed to prenatal androgens show that prenatal androgenization of 46,XX fetuses leads to marked masculinization of later gender-related behavior but does not lead to gender confusion/dysphoria. The example of female-to-male transsexuals, without evidence of prenatal androgen exposure, indicates that a male gender identity can develop without a significant androgen stimulus. So we are far away from any comprehensive understanding of hormonal imprinting on gender identity formation. Brain studies in homosexuals have not held up in replication studies or are in need of replication in transsexuals. Genetic studies and the fraternal birth order hypothesis provide indications of familial clustering of homosexuality but in many homosexuals these genetic patterns cannot be identified. The biological explanations advanced for the birth order hypothesis lack any experimental support.     

The association between the fraternal birth order effect in male homosexuality and other markers of human sexual orientation

Later fraternal birth order (FBO) is a well-established correlate of homosexuality in human males and may implicate a maternal immunization response in the feminization of male sexuality. This has led to the suggestion that FBO may relate to other markers of male sexual orientation which are robustly sexually dimorphic. If so, among homosexual males the number of older brothers should strongly correlate with traits such as spatial ability and psychological gender, indicative of greater behavioural feminization, compared to heterosexual males. The present study failed to find significant associations between number of older brothers and these traits.     

同性恋形成的行为神经内分泌机制

本文主要从生物学角度出发,从遗传学、神经内分泌学、行为学和神经解剖学方面综述了同性恋发生的神经内分泌机制。除了遗传和环境影响之外,围产期异常的性激素环境导致了性倾向的异常。在个体发育过程中通过下丘脑-垂体-性腺轴和下丘脑-垂体-肾上腺轴的作用,性腺类固醇激素和多种神经递质相互作用调节个体的性倾向的形成。同时,本文还提出目前该领域的研究进展、有待于解决的问题,以及进一步的研究方向,希望有助于人们正确认识同性恋的发生,关注同性恋生理和心理健康,预防青少年同性恋的发生。     

La médicalisation de la sexualité: Aspects sociologiques et historiques

The paper gives an introduction to a discussion about the process of medicalization of sexuality. This process is defined as: a social construction of knowledge on sexuality based on a biological conception of the body and health; clinical practice based on diagnosis and medical technologies; a strong relation between medecine and sexual morality. The paper is based on a study of the medical treatment of masturbation, sterilization and homosexuality in a historical perspective. Then the paper, shows how, currently, the process of medicalization of sexuality is twofold: on one hand stimulation of «normal» sexual activity (pharmacological treatment of sexual dysfunction) and inhibition of deviant sexual behavior (sexual abusers). At last, the paper, gives a short view on the potential transformations of the patient-doctor interaction.     

Handsome wants as handsome does: physical attractiveness and gender differences in revealed sexual preferences

In this article I evaluate the effect of physical attractiveness on young adults' sexual and romantic outcomes to reveal gender differences in acted preferences. Using data from the National Longitudinal Study of Adolescent Health (Add Health), a probability sample of young adults (n = 14,276), I investigate gender differences in desired sexual partner accumulation, relationship status, and timing of sexual intercourse. I find gender differences in sexual and romantic strategies consistent with those predicted by the double standard of sexuality and evolutionary theory. Specifically, compared to men, women pursue more committed relationships, fewer sexual partners, and delayed sexual intercourse.     

Sexuality in Norwegian textbooks: constructing and controlling ethnic borders?

In this article we discuss how sexuality is linked to national identity, ethnicity and cultural diversity in Norwegian textbooks for 13–16-year-olds. We show how gender equality and gay rights are mobilized as markers of Norwegianness in pedagogic texts and discuss the significance this has for inclusion in Norwegian nationhood. We address how progressive policies concerning gender and sexuality in Norway have been utilized to define Norwegianness in ethnic terms and argue that the texts we have analysed may produce the effect that tolerance towards homosexuality and support for gender equality as political positions are considered necessary for ethnic minority subjects’ acceptance as properly ‘integrated’ Norwegian citizens. In this way, these texts on sexuality may be seen to both construct and control ethnic borders in Norwegian society.     

Handsome Wants as Handsome Does: Physical Attractiveness and Gender Differences in Revealed Sexual Preferences

In this article I evaluate the effect of physical attractiveness on young adults' sexual and romantic outcomes to reveal gender differences in acted preferences. Using data from the National Longitudinal Study of Adolescent Health (Add Health), a probability sample of young adults (n?=?14,276), I investigate gender differences in desired sexual partner accumulation, relationship status, and timing of sexual intercourse. I find gender differences in sexual and romantic strategies consistent with those predicted by the double standard of sexuality and evolutionary theory. Specifically, compared to men, women pursue more committed relationships, fewer sexual partners, and delayed sexual intercourse.     

Fraternal birth order and the maternal immune hypothesis of male homosexuality

In men, sexual orientation correlates with an individual's number of older brothers, each additional older brother increasing the odds of homosexuality by approximately 33%. It has been hypothesized that this fraternal birth order effect reflects the progressive immunization of some mothers to Y-linked minor histocompatibility antigens (H-Y antigens) by each succeeding male fetus and the concomitantly increasing effects of such maternal immunization on the future sexual orientation of each succeeding male fetus. According to this hypothesis, anti-H-Y antibodies produced by the mother pass through the placental barrier to the fetus and affect aspects of sexual differentiation in the fetal brain. This explanation is consistent with a variety of evidence, including the apparent irrelevance of older sisters to the sexual orientation of later born males, the probable involvement of H-Y antigen in the development of sex-typical traits, and the detrimental effects of immunization of female mice to H-Y antigen on the reproductive performance of subsequent male offspring. The maternal immune hypothesis might also explain the recent finding that heterosexual males with older brothers weigh less at birth than heterosexual males with older sisters and homosexual males with older brothers weigh even less than heterosexual males with older brothers.     

Moral Darwinism: Ethical evidence for the descent of man

Could an ethical theory ever play a substantial evidential role in a scientific argument for an empirical hypothesis? InThe Descent of Man, Darwin includes an extended discussion of the nature of human morality, and the ethical theory which he sketches is not simply developed as an interesting ramification of his theory of evolution, but is used as a key part of his evidence for human descent from animal ancestors. Darwin must rebut the argument that, because of our moral nature, humans are essentially different in kind from other animals and so had to have had a different origin. I trace his causal story of how the moral sense could develop out of social instincts by evolutionary mechanisms of group selection, and show that the form of Utilitarianism he proposes involves a radical reduction of the standard of value to the concept of biological fitness. I argue that this causal analysis, although a weakness from a normative standpoint, is a strength when judged for its intended purpose as part of an evidential argument to confirm the hypothesis of human descent.     

The evolutionary psychology of sexual harassment in organizations

We explore the value of theory developed in the field of evolutionary psychology for predicting and explaining patterns of sociosexual interaction between men and women in the workplace. In particular, we focus on assessing the value of this theoretical framework for increasing our understanding of the behavioral phenomenon of sexual harassment in organizations. To do this, we develop hypotheses based on a consideration of the evolved psychological mechanisms which have been proposed by evolutionary psychologists to underly human sexual behavior. We then review the existing literature on sociosexual behavior and sexual harassment within the workplace as a preliminary test of predictions concerning the expected profile, reaction, and motivation of recipients and initiators of sexual advances in the workplace. We also analyze the expected effect of novel aspects of the organizational environment on overt sexual behavior. This theory predicts, for example, that most sexual harassment will be initiated by men, and that young, single women will be the most frequent victims. This theory also predicts that women will generally experience a more negative reaction than men to sexual advances in the workplace, but that this emotional response will be mediated by other factors such as the profile of the initiator. The available data generally confirm these and other related predictions. Moreover, these results are quite consistent with other studies of the evolutionary psychology of human sexuality. We discuss the implications for theory in this area, and suggest some potentially fruitful avenues for original empirical research on human sexual behavior, inside or outside the workplace.     

Darwin's ‘mystery of mysteries’: the role of sexual selection in plant speciation

Sexual selection is considered one of the key processes that contribute to the emergence of new species. While the connection between sexual selection and speciation has been supported by comparative studies, the mechanisms that mediate this connection remain unresolved, especially in plants. Similarly, it is not clear how speciation processes within plant populations translate into large-scale speciation dynamics. Here, we review the mechanisms through which sexual selection, pollination, and mate choice unfold and interact, and how they may ultimately produce reproductive isolation in plants. We also overview reproductive strategies that might influence sexual selection in plants and illustrate how functional traits might connect speciation at the population level (population differentiation, evolution of reproductive barriers; i.e. microevolution) with evolution above the species level (macroevolution). We also identify outstanding questions in the field, and suitable data and tools for their resolution. Altogether, this effort motivates further research focused on plants, which might potentially broaden our general understanding of speciation by sexual selection, a major concept in evolutionary biology.     

The tri‐trophic niche concept and adaptive radiation of phytophagous insects

A conceptual divide exists between ecological and evolutionary approaches to understanding adaptive radiation, although the phenomenon is inherently both ecological and evolutionary. This divide is evident in studies of phytophagous insects, a highly diverse group that has been frequently investigated with the implicit or explicit goal of understanding its diversity. Whereas ecological studies of phytophagous insects increasingly recognize the importance of tri‐trophic interactions as determinants of niche dimensions such as host‐plant associations, evolutionary studies typically neglect the third trophic level. Here we attempt to reconcile ecological and evolutionary approaches through the concept of the ecological niche. We specifically present a tri‐trophic niche concept as a foil to the traditional bi‐trophic niche concept for phytophagous insects. We argue that these niche concepts have different implications for understanding herbivore community structure, population divergence, and evolutionary diversification. To this end, we offer contrasting empirical predictions of bi‐ and tri‐trophic niche concepts for patterns of community structure, the process of population divergence, and patterns of evolutionary diversification of phytophagous insects.     

The ratio of 2nd to 4th digit length and male homosexuality

Sexual orientation may be influenced by prenatal levels of testosterone and oestrogen. There is evidence that the ratio of the length of 2nd and 4th digits (2D:4D) is negatively related to prenatal testosterone and positively to oestrogen. We report that (a) 2D:4D was lower in a sample of 88 homosexual men than in 88 sex- and age-matched controls recruited without regard to sexual orientation, (b) within the homosexual sample, there was a significant positive relationship between mean 2D:4D ratio and exclusive homosexuality, (c) overall, there was a decrease in 2D:4D from controls to homosexual men to bisexual men and (d) fraternal birth order, a positive predictor of male homosexuality, was not associated with 2D:4D in a sample of 240 Caucasian men recruited without regard to sexual orientation and 45 homosexual men.Further work is needed to confirm the relationships between 2D:4D and sexual orientation. However, these and other recent data tend to support an association between male homosexuality and high fetal testosterone. Very high testosterone levels may be associated with a sexual preference for both men and women.     

Perceived Sexual Orientation Based on Vocal and Facial Stimuli Is Linked to Self-Rated Sexual Orientation in Czech Men

Previous research has shown that lay people can accurately assess male sexual orientation based on limited information, such as face, voice, or behavioral display. Gender-atypical traits are thought to serve as cues to sexual orientation. We investigated the presumed mechanisms of sexual orientation attribution using a standardized set of facial and vocal stimuli of Czech men. Both types of stimuli were rated for sexual orientation and masculinity-femininity by non-student heterosexual women and homosexual men. Our data showed that by evaluating vocal stimuli both women and homosexual men can judge sexual orientation of the target men in agreement with their self-reported sexual orientation. Nevertheless, only homosexual men accurately attributed sexual orientation of the two groups from facial images. Interestingly, facial images of homosexual targets were rated as more masculine than heterosexual targets. This indicates that attributions of sexual orientation are affected by stereotyped association between femininity and male homosexuality; however, reliance on such cues can lead to frequent misjudgments as was the case with the female raters. Although our study is based on a community sample recruited in a non-English speaking country, the results are generally consistent with the previous research and thus corroborate the validity of sexual orientation attributions.     

Richard Owen, Morphology and Evolution

Richard Owen has been condemned by Darwinians as an anti-evolutionist and an essentialist. In recent years he has been the object of a revisionist analysis intended to uncover evolutionary elements in his scientific enterprise. In this paper I will examine Owen's evolutionary hypothesis and its connections with von Baer's idea of divergent development. To give appropriate importance to Owen's evolutionism is the first condition to develop an up-to-date understanding of his scientific enterprise, that is to disentagle Owen's contribution to the modernization of typology and morphology. I will argue that Owen's Platonic essentialism is rhetorical and incongruous. On the contrary, an interpretation of the archetype based on Aristotle's biological works makes possible a new conception of type, based on a homeostatic mechanism of stability. The renewal of morphology hinges on homological correspondences and a homeostatic process is also the origin of serial and special homology. I will argue that special homology shows an evolutionary orientation insofar as it is a typically inter-specific character while serial homology is determined through an elementary usage of the categories of developmental morphology. This revised version was published online in July 2006 with corrections to the Cover Date.     

A PSYCHIATRIC EVALUATION OF THE KINSEY REPORT

In Kinsey''s investigations there seems to be a tendency to study human sexuality from a biological point of view and to neglect the psychological with which sexuality is intimately involved. He does not sufficiently differentiate between sexual behavior in animals and humans which appear to be similar but which are really very different. His sociological conclusions suffer from this limited approach. Experience with patients strongly suggests that his statistics on women may include gross distortion. From a clinical psychiatric standpoint his concept of perversions is oversimplified. To Kinsey, all sexual activity represents the expression of sexual desire whereas it not uncommonly may be used to relieve tensions which are not of sexual origin.     

The virtues and limitations of exploring the eco‐evolutionary dynamics of sexually selected traits

Most studies on eco‐evolutionary feedbacks concern the influence of abiotic factors, or predator–prey and host–parasite interactions, while studies involving sexual interactions are lagging behind. This is at odds with the potential of these interactions to engage in such processes. Indeed, there is now ample evidence that sexual selection is affected by ecological change and that sexually selected traits can evolve rapidly, which may modify the ecological context of populations, and thus the selection pressures they will be exposed to. Here we review evidence for such eco‐evolutionary processes. We discuss examples of eco‐evolutionary change in an attempt to understand the challenges related with identifying and characterizing such processes. In particular, we focus on the challenges associated with accurately identifying the components of the feedback as well as their causal relation. Finally, we evaluate scenarios where understanding eco‐evolutionary feedbacks of sexual selection may help us appreciate the effects of sexual selection in shaping evolutionary processes.