Sex differences in throwing: monkeys having a fling

Fast and accurate throwing was undoubtedly important to ancestral hominids, and was subject to sexual-selection pressures that generated a male advantage in throwing accuracy that persists in modern humans. The balance of evidence, including that from a recent comparative study of throwing in humans and capuchin monkeys, suggests that high-performance throwing involves unique adaptations in the domains of spatial targeting, precision timing, and multi-joint motor control.     

Sex differences in the course of personality development: a meta-analysis.

Size and stability of sex differences in personality growth throughout adolescence and adulthood are examined. Studies using the Washington University Sentence Completion Test of ego development served as the primary source data. Sixty-five studies (encompassing more than 9,000 Ss) generated 113 independent effect sizes. Sex differences in ego development were moderately large among junior and senior high-school students (female advantage), declined significantly among college-age adults, and disappeared entirely among older men and women. Sex differences were relatively stable during early and middle adolescence. The greater maturity displayed by adolescent girls is not an artifact of superior verbal abilities. Sex differences in ego development were more than twice the magnitude of differences in vocabulary skills (Hyde & Linn, 1988). The present findings, together with findings from reviews of sex differences in moral judgment, aggression, and empathy, suggest that adolescent girls achieve developmental milestones earlier than boys, a difference that declines with age.     

Sex differences in depression

The role of housewife has been hypothesized as the source of excess mental illness among married women as compared with married men. The present study found both housewives and working wives significantly more depressed than working husbands. Although working wives report that they do more housework than husbands, this factor was not significantly related to depression for either wives or husbands. It is suggested that the risk factors for depression, including marriage for women, may be better understood in the context of clinical theories of depression, especially the learned helplessness model.     

Sex differences in self-silencing

The construct of self-silencing was proposed to account for women's greater vulnerability to developing depression. This study of 1,117 students (795 women and 322 men) explored possible explanations for the empirical finding that men self-silence to the same or greater extent than women. Analysis showed that men reported more self-silencing than women. A factor analysis confirmed the subscale structure of the Silencing the Self Scale for women and men, with relatively few departures from the originally proposed subscales. Depression and self-silencing scores were correlated positively for both men and women. The results of two multiple regressions, performed separately for men and women, showed that depressive symptomatology accounted for a significant percentage of the variance in self-silencing but that social desirability did not account for a significant increment in the variance accounted for in silencing the self. The scores on the Care as Self-sacrifice and the Divided Self subscales were intercorrelated for women, but not for men, indicating that there may be a sex difference in perception of self-silencing behavior.     

Sex differences in pain

Are there sex differences in pain? For experimentally delivered somatic stimuli, females have lower thresholds, greater ability to discriminate, higher pain ratings, and less tolerance of noxious stimuli than males. These differences, however, are small, exist only for certain forms of stimulation and are affected by many situational variables such as presence of disease, experimental setting, and even nutritive status. For endogenous pains, women report more multiple pains in more body regions than men. With no obvious underlying rationale, some painful diseases are more prevalent among females, others among males and, for many diseases, symptoms differ between females and males. Sex differences in attitudes exist that affect not only reporting, coping, and responses to treatment, but also measurement and treatment. So many variables are operative, however, that the most striking feature of sex differences in reported pain experience is the apparent overall lack of them. On the other hand, deduction from known biological sex differences suggests that these are powerful sex differences in the operation of pain mechanisms. First, the vaginal canal provides an additional route in women for internal trauma and invasion by pathological agents that puts them at greater risk for developing hyperalgesia in multiple body regions. Second, sex differences in temporal patterns are likely to give rise to sex differences in how pain is "learned" and stimuli are interpreted, a situation that could lead to a greater variability and wider range of pains without obvious peripheral pathology among females. Third, sex differences in the actions of sex hormones suggest pain-relevant differences in the operation of many neuroactive agents, opiate and nonopiate systems, nerve growth factor, and the sympathetic system. Thus, while inductive analysis of existing data demonstrate more similarities than differences in pain experience between females and males, deductive analysis suggests important operational sex differences in its production.     

Sex differences in cognition

Sex differences in cognitive skills, grouped into three areas — motor, spatial, and linguistic — are assessed in the context of current notions of cerebral lateralization (Buffery and Gray, 1972). There are few convincing sex differences, either overall, or in interactions with (putative) functional localization. There are several qualifying criteria (nature of further interactions with age, birth order, culture, sex of experimenter, sex role pressure) which would have to be met, but these are as yet inadequately documented. Serious caution is urged on the proliferating number of researchers in this area.     

Sex differences in the adolescent brain

Adolescence is a time of increased divergence between males and females in physical characteristics, behavior, and risk for psychopathology. Here we will review data regarding sex differences in brain structure and function during this period of the lifespan. The most consistent sex difference in brain morphometry is the 9–12% larger brain size that has been reported in males. Individual brain regions that have most consistently been reported as different in males and females include the basal ganglia, hippocampus, and amygdala. Diffusion tensor imaging and magnetization transfer imaging studies have also shown sex differences in white matter development during adolescence. Functional imaging studies have shown different patterns of activation without differences in performance, suggesting male and female brains may use slightly different strategies for achieving similar cognitive abilities. Longitudinal studies have shown sex differences in the trajectory of brain development, with females reaching peak values of brain volumes earlier than males. Although compelling, these sex differences are present as group averages and should not be taken as indicative of relative capacities of males or females.     

Sex differences in the perception of touching

Sex differences in the perception of touching were investigated by having 25 male and 25 female college students rate how likeable a touch would be under different conditions. The women produced a more favorable affect than the men when they touched, and women were perceived as liking to be touched more than men. Perception of touching in general was correlated positively with Self-esteem for men, negatively with Machiavellianism for women, and positively with Trust for women. Results were discussed in terms of traditional sex-typing of touching behavior.     

Sex differences in the processing of flankers

The study of sex differences in cognition has often focused on differences in spatial processing. Recently, sex differences in selective attention have been observed by Bayliss, di Pellegrino, and Tipper (2005), showing that women are more influenced than men by irrelevant spatial cues. The current study elaborates on this finding and tests whether sex differences in the processing of irrelevant information also occur in a simpler task, in which there is no need to redirect visual attention and no need to remember multiple spatial stimulus–response associations. Here, attention is studied using a novel combination of a go/no-go task and a flanker task. A total of 80 neurotypical participants were studied, and it was found that responses in women were more strongly affected by flanker information than were responses in men. This suggests that these sex differences were not due to difficulties with spatial reorientation, or remembering spatial stimulus–response relationships. The findings are discussed in the context of the hunter–gatherer theory of sex differences.     

Sex differences in the generalization of attraction

The effects of intergroup evaluations on intragroup attraction were assessed in a situation involving two-person teams that were all of the same sex. Male (N=123) and female (N=118) group members separately reported their political views to another dyad and then received either unfavorable, favorable, or no feedback regarding their team as a whole on the basis of this information. The results indicated that females evidenced more anger in response to the out-group's unfavorable feedback than did males. These anger responses were related to attraction to ward a teammate for males but not for females. Moreover, males evidenced less attraction toward an in-group member after receiving unfavorable rather than favorable intergroup evaluations, whereas females did not. On the other hand, only for females was attraction to ward a teammate related to the perceived similarity of that individual within experimental conditions. Apparently, the greater cognitive orientation of females as compared to males to ward another ingroup member resulted in their being less susceptable to the influence of situationally induced affect.This research was performed as part of the author's doctoral dissertation submitted to the Department of Psychology, Purdue University. Portions of this paper were presented at the meeting of the Eastern Psychological Association held in Boston, 1977.It should be noted that the views expressed in this paper are those of the author and do not reflect those of the Army or any other government agency.     

Sex differences in the self-concept in adolescence

This paper examines an aspect of the self-concept — salience of the self or self-consciousness — which has generally been neglected in the past. In an empirical study of nearly 2,000 children and adolescents, it was found that striking sex differences emerge during the adolescent period. Girls are considerably more self-conscious than boys, more vulnerable to criticism, and more concerned with promoting interpersonal harmony. Overall, adolescent girls are increasingly “people-oriented” while boys stress achievement and competence. It is suggested that these differences reflect the social definitions of sex roles.     

Sex differences in early verbal and non‐verbal cognitive development

The present study of over 3000 2‐year‐old twin pairs used a sex‐limitation model to examine genetic and environmental origins of sex differences in verbal and non‐verbal cognitive ability. Girls scored significantly higher on both measures (p<0.0001), although gender only accounted for approximately 3% of the variance in verbal ability and 1% of the variance in non‐verbal cognitive ability. For the verbal measure boys showed greater heritability than girls. Also the twin‐pair correlation is significantly lower for opposite‐sex twins than for non‐identical same‐sex twins. This indicates that individual differences in verbal ability include some sex‐specific factors. Non‐verbal cognitive ability did not differ in aetiology for boys and girls. We conclude that genetic and environmental influences differ for girls and boys for early verbal but not non‐verbal development.     

Sex differences in preadolescent self-disclosure

Both amount and content of self-disclosure may vary with sex role. Both adult and preadolescent females have been reported as engaging in greater amounts of self-disclosure than males; the present study attempted to replicate these findings with preadolescents, and to investigate sex differences in the content of self-disclosure. A self-disclosure questionnaire covering a wide range of subjects was administered to 307 urban children. The sex difference on the total number of items revealed to a friend closely approached significance, with girls showing greater disclosure. When only intimate content items were examined, the sex difference reached clear significance. Content analysis showed that girls were more willing to reveal items related to emotionality, anxiety, and dependence.