The purposes of this paper are 1) to introduce the methods for determining sex/gender differences from the perspective of behavioral genetics, 2) to review the sex/gender differences in various psychological traits found by these approaches, and 3) to propose directions for psychological gender research using behavioral genetics. While behavioral genetics always focuses on individual gender differences, using sex/gender limitation analysis, such studies can focus on both quantitative and qualitative factors affected by sex/gender differences. By integrated the findings derived from behavioral genetics, gender studies can determine how the environment influences genetic factors, and can describe the developmental trajectories of genetic and environmental factors related to gender.

In this paper, the evolutionary roots of gender differences in aggressive behavior are presented. Previous studies in the field of social psychology have shown that men are more aggressive than women not only in interpersonal, but also in intergroup relationships. From an evolutionary psychological view, it is predicted that outgroup aggression is triggered by the psychological mechanisms adapted to intergroup conflict specified for males. However, social psychologists demonstrated that ingroup cooperation, but not outgroup aggression, was dominant in intergroup conflict situations in a laboratory experiment. On the other hand, in these days, some evidence in the field of cultural anthropology, ethnography, and bioarcheology have clearly shown that hunter-gatherer and forager males frequently engaged in war. I discuss whether intergroup conflict influences selection pressure on male aggressive behavior as a reproductive strategy to enhance fitness.

The purpose of this article is to review studies on the effects of salience of heterosexuality and mating motives on both social cognition and social behaviors and to discuss implications for gender differences in the findings of these studies. First, cultural and evolutional theories that emphasized the role of heterosexuality as a factor causing gender differences are described. Next, I review experimental studies examining the effects of mate seeking motive and mate retention motive on attention, processing style, categorization, self- representation, and social behavior (e.g., strategic self-presentations, risk taking behaviors, and aggressive behaviors). The findings from this review are discussed in terms of context-dependency of gender differences. Finally, I suggest future directions for research in both gender and evolutionary psychology.

It is unclear why the number of women in the fields of Science, Technology, Engineering, and Mathematics (STEM) is still small. In this review article, I focus on gender stereotypes (i.e., the belief that “women canʼt do math”) from a social psychological perspective. It has been reported that women and girls are influenced by negative stereotypes in experimental settings as well as in the real world. For example, researchers have found that negative stereotypes can undermine the performance of women in math exams. More recently, implicit stereotypes have been found to affect womenʼs math preferences either equally or even more than explicit stereotypes. How can we counteract the effects of negative stereotypes? Interventions, such as informing women that their math performances and career decisions are often unconsciously influenced by gender stereotypes, have been introduced based on accumulated knowledge of both gender and stereotypes. Having reviewed such literature, I conclude that psychologists in Japan should put more effort into conducting research on how to encourage women and girls to pursue their career plans, especially in the STEM field.

Despite the increasing participation of women in the workforce and the establishment of laws prohibiting gender discrimination, it is not clear why gender inequality still persists in Japanese society. To address this question, this paper explains the mechanisms of the persistence of gender inequality from the perspective of work and family. First, the rapid changes in the Japanese society, laws, and economic structure over the past four decades are presented. Next, I review literature on the psychology and sociology of gender role attitudes and the longitudinal changes in these attitudes. In addition, seven gender disparities in the workplace (e.g., gender wage gap and proportion of women in managerial positions) are discussed in relation to family roles.

The overall results reveal that the following five factors contribute to the persistence of gender inequalities: 1. division of labor by gender; 2. long working hours, employment systems, and employment practices; 3. gender role stereotypes and expectations; 4. inconsistent management practices between positive attitudes towards promoting women and traditional gender role attitudes; and 5. traditional gender role attitudes and gender identity of a woman as a wife.

The distinction between sex and gender differences is very ambiguous in the Japanese language as discussed in this special issue. It is important that we use these two terms correctly, i.e., sex differences have a biological basis, and gender differences are based on social behaviors and conventions. Within this special issue, the distinction between sex differences and gender differences are presented by several authors. Sasaki emphasizes the usefulness of sex/gender limitation analysis which could redefine sex/gender differences. Morinaga tries to explain women’s relative inferiority in the fields of science and mathematics by the stereotypic misnomer “not being good at mathematics”. Suzuki reviews the psychological factors, such as gender role attitudes that affect gender inequality. Yokota examines the popular “male warrior” hypothesis in evolutionary psychology through new findings in both experimental psychology and archeology. Numazaki’s article explains the origins of sex differences through both cultural and evolutionary approaches. Each article advances our understanding of the origins of sex/gender differences. On the other hand, the studies that redefine the origins of both sexist societies and institutions and promote ways to change gender differences, should be further evaluated. To that end, more in depth interactions among behavioral geneticists, evolutionary psychologists, and social psychologists are needed.

The various underlying causes of both gender differences and gender inequality were investigated by analyzing previous studies on social perspectives, gender stereotypes, heterosexuality, and marital motives. To date, researchers have used different approaches for analysis of the public and private aspects of gender differences. For public aspects, they have investigated complaints about gender discrimination as a human rights issue in social settings. Private aspects have been related to the issue of forming male-female couples, i.e. heterosexual or marital motives. All of the above approaches are considered as the field of social psychology. This study attempted to approach these issues from the perspective of developmental psychology.

This article provides commentary for the special issue entitled, “Mechanisms underlying emergence of gender and sex differences,” from the perspective of the nature vs. culture debate on the differences between men and women. A brief review of the literature suggests that although biological and cultural explanations have often been viewed as binary opposites, many contemporary theorists view them as both compatible and complementary. From this viewpoint, I discuss the significance of all of the articles in the present special issue and how they relate to future directions in the field. My conclusion is that most of the articles are fairly impartial and have the potential to transcend the nature vs. culture debate.

The progress of brain-imaging research casts doubt on a theory that the degree of brain-lateralization defines sex differences in cognitive strength patterns, i.e., men excel at spatial ability and math, and women excel at verbal fluency and language abilities. Meta-analyses reported that previously believed anatomical brain sex-differences, including the thickness of the corpus callosum, were not replicated. However, findings did not completely exclude the existence of brain/cognitive sex differences. The author reviews recent trends in this debate and covers new evidence that bridges the biological and cultural approaches, including “stereotype threat” investigations for explaining the STEM gender gap. The importance of both defining the scope of interest and dissecting various elements that relate to manifestations of socio-behavioral patterns is stressed.

Sometimes, we discriminate “sex differences” from “gender differences” implying that there are two types of differences between women and men: biologically based sex differences and socially constructed gender differences. One may even imply that biologically based sex differences are more “innate” and more difficult to change. In this article, I will argue that biological sex differences are not genetically determined. Rather, biological sex differences are products of genetic, ecological, and social influences. Organisms flexibly and adaptively change their sexual behavior to meet their environmental requirements. More importantly, theoretical biology has produced many hypotheses on how individual organisms adjust their behavior according to both ecological and social environmental changes. Those theories are testable on human behavior and will bring significant insights to “gender” difference studies.