Coitus-induced ovulation

Sexual Desire of Women With Fast and Slow Life History Throughout the Ovulatory Cycle

Findings on female sexual motivation across the ovulatory cycle are mixed. Some studies have reported increased female sexual desire on fertile days or midway through the ovulatory cycle, whereas others have reported increased sexual desire on nonfertile days. We postulated and tested the hypothesis that the pattern of the cyclical change of female sexual desire is associated with women's life history. Female participants completed life-history measures and rated their levels of sexual desire on the survey day and reported the first day of their current and subsequent cycle, respectively (Study 1), or recorded their sexual desire throughout an entire cycle by submitting daily reports (Study 2). Results indicate that women with a fast life history experienced peak sexual desire midcycle, whereas women with a slow life history experienced two peaks of sexual desire midcycle and around their menses. These findings suggest that, consistent with the underlying life history, cyclically differential peaking of sexual desire may serve different reproductive functions.

Pilot Study of Relationship between Fertility Risk and Bargaining

Competition for resources to support a healthy pregnancy and later offspring was likely very important for ancestral women. Therefore, it was predicted that women evolved a propensity for intrasexual competition over resources during times of their highest conception risk. To investigate this hypothesis, women played a series of ultimatum games, bargaining games that test participants' willingness to share a monetary stake. During periods of high conception risk, intrasexual competition increased as evidenced by lower offers to share a stake with others as well as higher rates of rejection of offers.

Fertility Cycle Patterns in Motives for Sexual Behavior

Three studies examined the relationship between fertility, as indexed by day in cycle or salivary estradiol levels, and reported motives for sexual intercourse. Data from university and community samples in both cross-sectional and repeated-measures designs showed that sex-for-intimacy motives are endorsed significantly less by women who are relatively more fertile or show higher salivary estrogen levels. Sex for enhancement, self-affirmation, and partner approval also declined, although the data were less consistent. The remaining motives (coping and power) showed no consistent patterns across fertility status. Results suggest that sexual motives are rooted partly in woman's biology and are discussed in terms of plausible evolutionary mechanisms that might promote female “choosiness” at midcycle.

Women's Preferences for Male Behavioral Displays Change Across the Menstrual Cycle

Women prefer both the scent of symmetrical men and masculine male faces more during the fertile (late follicular and ovulatory) phases of their menstrual cycles than during their infertile (e.g., luteal) phases. Men's behavioral displays in social settings may convey signals that affect women's attraction to men even more strongly. This study examined shifts in women's preferences for these behavioral displays. A sample of 237 normally ovulating women viewed 36 or 40 videotaped men who were competing for a potential lunch date and then rated each man's attractiveness as a short-term and a long-term mate. As predicted, women's preference for men who displayed social presence and direct intrasexual competitiveness increased on high-fertility days relative to low-fertility days, but only in a short-term, not a long-term, mating context. These findings add to the growing literature indicating that women's mate preferences systematically vary across the reproductive cycle.

Women's fertility across the cycle increases the short-term attractiveness of creative intelligence

Male provisioning ability may have evolved as a "good dad" indicator through sexual selection, whereas male creativity may have evolved partly as a "good genes" indicator. If so, women near peak fertility (midcycle) should prefer creativity over wealth, especially in short-term mating. Forty-one normally cycling women read vignettes describing creative but poor men vs. uncreative but rich men. Women's estimated fertility predicted their short-term (but not long-term) preference for creativity over wealth, in both their desirability ratings of individual men (r=.40, p<.01) and their forced-choice decisions between men (r=.46, p<.01). These preliminary results are consistent with the view that creativity evolved at least partly as a good genes indicator through mate choice.

Comment: Wood et al.’s (2014) Speculations of Inappropriate Research Practices in Ovulatory Cycle Studies

Wood, Kressel, Joshi, and Louie (2014) meta-analyzed studies examining changes in women’s mate preferences as a function of cycle phase, and claimed to find little evidence for shifts, contrary to Gildersleeve, Haselton, and Fales’s (2014a) meta-analysis. This commentary concerns specific speculations Wood et al. made about particular researchers analyzing data multiple ways, capitalizing on chance and thereby inflating the Type I error rate. In so doing, Wood et al. misconstrued a key article explaining the high fertility period, misrepresented studies, and presented no supportive evidence. The corrosive effects of inappropriate research practices on scientific literatures are concerning. So too are unsubstantiated speculations of them.

Meta-Analysis of Menstrual Cycle Effects on Women’s Mate Preferences

In evolutionary psychology predictions, women’s mate preferences shift between fertile and nonfertile times of the month to reflect ancestral fitness benefits. Our meta-analytic test involving 58 independent reports (13 unpublished, 45 published) was largely nonsupportive. Specifically, fertile women did not especially desire sex in short-term relationships with men purported to be of high genetic quality (i.e., high testosterone, masculinity, dominance, symmetry). The few significant preference shifts appeared to be research artifacts. The effects declined over time in published work, were limited to studies that used broader, less precise definitions of the fertile phase, and were found only in published research.

The case of Moulay Ismael--fact or fancy?

Textbooks on evolutionary psychology and biology cite the case of the Sharifian Emperor of Morocco, Moulay Ismael the Bloodthirsty (1672–1727) who was supposed to have sired 888 children. This example for male reproduction has been challenged and led to a still unresolved discussion. The scientific debate is shaped by assumptions about reproductive constraints which cannot be tested directly—and the figures used are sometimes arbitrary. Therefore we developed a computer simulation which tests how many copulations per day were necessary to reach the reported reproductive outcome. We based our calculations on a report dating 1704, thus computing whether it was possible to have 600 sons in a reproductive timespan of 32 years. The algorithm is based on three different models of conception and different social and biological constraints. In the first model we used a random mating pool with unrestricted access to females. In the second model we used a restricted harem pool. The results indicate that Moulay Ismael could have achieved this high reproductive success. A comparison of the three conception models highlights the necessity to consider female sexual habits when assessing fertility across the cycle. We also show that the harem size needed is far smaller than the reported numbers.

Comparing group dehumanization and intra-sexual competition among normally ovulating women and hormonal contraceptive users

Two studies address the role of hormonal shift across menstrual cycle in female dehumanization of other women. In Study 1, normally ovulating women (NOW) and women who use hormonal contraceptives (HCW) are compared in terms of how much they dehumanize other women and two other control targets (men and elderly people). In NOW, the level of dehumanization of other women, but not of men and elderly people, increases as the conception risk is enhanced. HCW do not show this pattern of results. In Study 2, we investigate the level of dehumanization of other women and of intra-sexual competition. Findings concerning dehumanization replicate those of Study 1. Intra-sexual competition increases with the rise of conception risk only in NOW. In addition, dehumanization is significantly associated with intra-sexual competition in NOW but not in HCW. Together, these studies demonstrate that dehumanization of women is elicited by menstrual cycle-related processes and associated with women's mate-attraction goals.

Changes in women's feelings about their romantic relationships across the ovulatory cycle

According to the dual mating hypothesis, women possess two overlapping suites of mate-choice mechanisms: one leading to preferences for sexually desirable men who have high-fitness genes and one leading to preferences for men who are able to invest in a woman and her children. Evidence increasingly demonstrates that women's preference for sexual desirability (but not investment attractiveness) increases when women are most fertile within the ovulatory cycle. Little is known, however, about the implications of these preference shifts for women's relationships with their long-term partners. Using luteinizing hormone tests to verify ovulation, across two studies (Samples 1 and 2), we found that women whose partners were relatively low in sexual desirability felt less close to their partner (Samples 1 and 2) and were more critical of their partner's faults (Sample 2) on high-fertility days of the cycle just prior to ovulation compared with low-fertility days of the cycle. Women whose partners were relatively high in sexual desirability felt closer to their partner (Sample 1) and more satisfied with their relationship (Sample 2) on high- than low-fertility days of the cycle. There were no such shifts in women's commitment to their relationship. Therefore, partner sexual desirability predicts women's high-fertility assessments of relationship quality but not their intentions to stay in their relationship, consistent with the dual mating hypothesis. These findings suggest that variations across the ovulation cycle in women's reproductive hormones play an important role in relationship dynamics.

Characterization of the estrous cycle in female beluga (Delphinapterus leucas) using urinary endocrine monitoring and transabdominal ultrasound: Evidence of facultative induced ovulation

Recent, successful application of assisted reproductive technologies in captive beluga has resulted from the extensive study of male beluga reproductive biology. Optimization of assisted reproduction requires additional detailed knowledge of the female estrous cycle. Our specific objectives were to: (1) validate urinary immunoassays for use in this species; (2) elucidate annual ovarian cycle dynamics through the combined use of hormone excretion patterns and transabdominal ultrasound; and (3) establish whether ovulation in this species is spontaneous or induced by male factors. Ovulation was observed in four of 15 estrous cycles monitored in four adult female beluga maintained in a single-sex group. After introduction of a breeding male, ovulation was observed in six of seven estrous cycles. All estrous cycles occurred from March through June. For spontaneous ovulations (n=4), the inter-estrous interval was 34d (range 33-35d), with a follicular phase length (FPL) of 25±8d (mean±SD). For all ovulatory estrous cycles (with and without a breeding male), urinary estrogen conjugates (EC, 15.3±7.9ng/mg Cr) and ovulatory luteinizing hormone (ovLH, 17.1±6.6ng/mg Cr) concentrations both peaked on Day 0, and EC concentrations returned to baseline 8±7d later. For non-conceptive cycles, urinary progestagen (Pg) concentrations increased on Day 0 (3.5±1.7ng/mg Cr), peaked on Day+19 (19.7±17.1ng/mg Cr), and were elevated above baseline for 27±4d. Preovulatory follicular diameter and circumference on Day -2±2 (range: Day -4 to -1) from peak EC were 2.5±0.7 and 7.8±1.3cm, respectively. The FPL in non-ovulatory estrous cycles (n=11) lasted 24±10d and EC concentrations gradually declined to baseline over a 21±10d interval following the EC peak (27.8±28.8ng/mg Cr). Non-ovulatory estrous cycles were characterized by the absence of an ovLH surge and no concomitant increase in Pg concentrations above baseline excretion; the mean follicular diameter at or near peak EC was 3.1±0.8cm on Day 2 ±3d from peak EC (range: -1 to +5days from peak EC). Overall, these data confirm that captive beluga exhibit reproductive seasonality and demonstrate that the species is a facultative-induced ovulator.

Ovulatory shifts in female sexual desire

Women's reproductive biology imposes heavy obligatory costs of parental investment, creating strong selective forces hypothesized to shape female mating psychology around critical decisions such as the choice of partner, the timing of sexual intercourse, and the timing of reproduction. We propose that female sexual desire has evolved as one adaptation among several designed to regulate these decisions. We hypothesize (a) an increase in desire as conception probability increases, but only among women who are in committed long-term relationships; and (b) a shift in the desire for a primary partner as compared with extra-pair partners as ovulation approaches, dependent upon a woman's evaluation of her primary partner's relative quality. We tested several predictions derived from these hypotheses in a study of 173 women who were not taking oral contraceptives. Results confirmed Hypothesis 1: An ovulatory peak in sexual desire was found only for mated women; for unmated women, conception probability and sexual desire were uncorrelated. Hypothesis 2 was partially supported. Among mated women, those with higher conception probability exhibited higher levels of in-pair sexual desire relative to those at lower conception probability. Conception probability and relationship length interacted significantly to predict extra-pair desires, such that women in longer relationships were more likely to experience desire for extra-pair partners during periods of high conception probability. The pursuit of an in-pair conceptive strategy (as opposed to an extra-pair conceptive strategy) was also associated with the occurrence of sexual activity in the relationship.

Person perception across the menstrual cycle: hormonal influences on social-cognitive functioning

Women's reactions to men shift during the menstrual cycle. For example, during the phase of high conception risk, women prefer men with masculinized facial features. A favored explanation for this effect is that women display an enhanced sensitivity to stimuli that have significant reproductive relevance during the phase of the menstrual cycle in which conception risk is high. Consistent with this viewpoint, the present research demonstrated that women's cycle-dependent attentiveness to "maleness" also extends to basic aspects of the person-perception process. Specifically, during the phase of high conception risk, women displayed an enhanced ability both to categorize men and to access associated category-related (i.e., stereotypic) material from semantic memory. The implications of these findings for contemporary treatments of person perception are considered.

Changes in women's sexual interests and their partners' mate-retention tactics across the menstrual cycle: evidence for shifting conflicts of interest

Because ancestral women could have obtained genetic benefits through extra-pair sex only near ovulation, but paid costs of extra-pair sex throughout the cycle, one might expect selection to have shaped female interest in partners, other than primary partners, to be greater near ovulation than during the luteal phase. Because men would have paid heavier costs if their partners had extra-pair sex near ovulation, one might also expect selection to have shaped males' efforts to track their primary partners' whereabouts to be increased near ovulation, relative to the luteal phase. Women filled out questionnaires about their sexual interests and their partners' mate-retention tactics twice: once within 5 days before a lutenizing hormone surge and once during the luteal phase. Results showed that: (i) women reported greater sexual interest in, and fantasy about, non-primary partners near ovulation than during the luteal phase; (ii) women did not report significantly greater sexual interest in, and fantasy about, primary partners near ovulation; (iii) women reported that their primary partners were both more attentive and more proprietary near ovulation.

Neuroendocrine regulation of GnRH release in induced ovulators

GnRH is the key neuropeptide controlling reproductive function in all vertebrate species. Two different neuroendocrine mechanisms have evolved among female mammals to regulate the mediobasal hypothalamic (MBH) release of GnRH leading to the preovulatory secretion of LH by the anterior pituitary gland. In females of spontaneously ovulating species, including rats, mice, guinea pigs, sheep, monkeys, and women, ovarian steroids secreted by maturing ovarian follicles induce a pulsatile pattern of GnRH release in the median eminence that, in turn, stimulates a preovulatory LH surge. In females of induced ovulating species, including rabbits, ferrets, cats, and camels, the preovulatory release of GnRH, and the resultant preovulatory LH surge, is induced by the receipt of genital somatosensory stimuli during mating. Induced ovulators generally do not show "spontaneous" steroid-induced LH surges during their reproductive cycles, suggesting that the positive feedback actions of steroid hormones on GnRH release are reduced or absent in these species. By contrast, mating-induced preovulatory surges occasionally occur in some spontaneously ovulating species. Most research in the field of GnRH neurobiology has been performed using spontaneous ovulators including rat, guinea pig, sheep, and rhesus monkey. This review summarizes the literature concerning the neuroendocrine mechanisms controlling GnRH biosynthesis and release in females of several induced ovulating species, and whenever possible it contrasts the results with those obtained for spontaneously ovulating species. It also considers the adaptive, evolutionary benefits and disadvantages of each type of ovulatory control mechanism. In females of induced ovulating species estradiol acts in the brain to induce aspects of proceptive and receptive sexual behavior. The primary mechanism involved in the preovulatory release of GnRH among induced ovulators involves the activation of midbrain and brainstem noradrenergic neurons in response to genital-somatosensory signals generated by receipt of an intromission from a male during mating. These noradrenergic neurons project to the MBH and, when activated, promote the release of GnRH from nerve terminals in the median eminence. In contrast to spontaneous ovulators, there is little evidence that endogenous opioid peptides normally inhibit MBH GnRH release among induced ovulators. Instead, the neural signals that induce a preovulatory LH surge in these species seem to be primarily excitatory. A complete understanding of the neuroendocrine control of ovulation will only be achieved in the future by comparative studies of several animal model systems in which mating-induced as well as spontaneous, hormonally stimulated activation of GnRH neurons drives the preovulatory LH surge.

Human sexual selection, good genes, and special design

Evolutionary psychology seeks to understand the functional design underlying psychological processes and behavior. Theories of selection pressures developed within evolutionary biology are key components of this understanding. Because past selection pressures responsible for current design cannot be directly observed, theoretical understandings of the psychological processes and behavior must be inferred. The most important epistemological concept within evolutionary psychology is that of special design-evidence that a feature exhibits specificity, efficiency, and economy for producing a particular beneficial effect. A variety of sexual-selection processes have been proposed to account for aspects of human mating. These processes are not mutually exclusive. More than one may account for aspects of human mating. A core task of evolutionary psychology within this domain is to identify which processes account for which phenomena. I have attempted to illustrate how the search for special design is central to this endeavor.

Menstrual cycle variation in women's preferences for the scent of symmetrical men

Evidence suggests that female sexual preferences change across the menstrual cycle. Women's extra-pair copulations tend to occur in their most fertile period, whereas their intra-pair copulations tend to be more evenly spread out across the cycle. This pattern is consistent with women preferentially seeking men who evidence phenotypic markers of genetic benefits just before and during ovulation. This study examined whether women's olfactory preferences for men's scent would tend to favour the scent of more symmetrical men, most notably during the women's fertile period. College women sniffed and rated the attractiveness of the scent of 41 T-shirts worn over a period of two nights by different men. Results indicated that normally cycling (non-pill using) women near the peak fertility of their cycle tended to prefer the scent of shirts worn by symmetrical men. Normally ovulating women at low fertility within their cycle, and women using a contraceptive pill, showed no significant preference for either symmetrical or asymmetrical men's scent. A separate analysis revealed that, within the set of normally cycling women, individual women's preference for symmetry correlated with their probability of conception, given the actuarial value associated with the day of the cycle they reported at the time they smelled the shirts. Potential sexual selection processes and proximate mechanisms accounting for these findings are discussed.

Pregnancy resulting from rape

Pregnancy resulting from rape is more prevalent than generally recognized, and violations of women's sexual and reproductive self-determination take many forms. Four themes--relationship rape, power dynamics, maternal ambivalence, and social reactions and support--can be identified in one woman's experiences and the literature. Recommended interventions, based on a woman-centered empowerment framework, include safety assessment, formulating a safety plan, and facilitating social support. Emergency postcoital contraception is a preventive option.

Coitus-induced ovulation and its implications for estimates of some reproductive parameters

It is estimated here that, at the time of conception, the mean coital rate of young women who subsequently bear DZ twins is about 6% higher than that of the general population of young married women. This differential seems too small to account wholly for the greater promptness in conceiving DZ twins. Accordingly, it is suggested that coital rate is associated with DZ twinning in two ways. The major link seems to be indirect and mediated by erotic response which causes an increase in gonadotrophin levels and thus in double ovulation. In a minority of cases, frequent coitus may give rise to DZ twins via superfecundation, but it seems that, in human beings, the corpus luteum of one ovum will usually inhibit fertilization of any further ova after a short interval. The evidence presented here, though indirect, seems to suggest that, under particularly erotic conditions, double ovulation is sometimes induced. It seems reasonable to infer that coitus also occasionally provokes or accelerates single ovulations, thus impugning some rhythm methods of contraception. But there seems no very good evidence that rape induces ovulation. Some notes are added on the implications of induced ovulation for estimates of fecundability and of the length of the fertile period.

Control of ovulation, vaginal estrus, and behavioral receptivity in voles (Microtus)

Rodents of the genus Microtus provide an excellent focus for the study of the effects of environmental and behavioral influences on reproductive physiology. Despite some early reports, there is little definitive evidence of truly spontaneous ovulation in Microtus. Stimuli from copulation with males appear capable of triggering ovulation in all species: the requisite amount of stimulation for ovulation and a functional luteal phase varies with the species. In addition, however, a certain percentage of the females of some, but not all, species ovulate when placed in proximity to males when copulation is presented. There are few reports of regular cycles of cell types in the vaginal smears of Microtus females; the relative preponderance of cornified, nucleated, and leukocytic cells varies with species and conditions. Behavioral receptivity is not invariably correlated with smear type. The complexity of environment-behavior relationships in different species suggests the need for a more comprehensive classification schema for systems of female reproductive physiology and a study of their adaptive significance.

Coitus-induced ovulation and sex ratio in man

It is hypothesised that the occurence of coitus-induced ovulation could be an important factor affecting the sex ratio in human progeny. The slight preponderance of males in human sex ratio at birth, 106 : 100, could be influenced considerably by the coitus-induced occurence.