OUTLINE Sexual Development Hormonal Effects on the Brain and Behavior Sexual Interest Orientation and Strategies Hormonal Effects on Cognitive Behavior Women Men Verbal tasks Related to higher levels of estrogen Men Women Spatial tasks Related to higher levels of androgens Hormonal Effects on Cognitive Behavior Do women show improved learning at different points of menstrual cycle Epting Overman 1998 Hormonal Effects on Cognitive Behavior Do women show improved learning at different points of menstrual cycle Male to female transsexuals hormone therapy M F Transexual Male Paired Associate Learning Hormones Sexual Orientation Sexual Behavior in Rodents Females are receptive to males only during estrus Lordosis receptive posture in which the hindquarter is raised and the tail is turned to the side facilitating intromission by the male Activational Effects of Human Sex Hormones Women Ovarian hormones do not control women s sexual activity but may influence sexual interest Testosterone activates sexual behavior Men Testosterone activates sexual behavior Androgens and Men Males and females both produce androgens and estrogens but in differing amounts Sex Hormones and Male Behavior Androgens and Cognitive Behavior Spatial abilities advantage may be related to testosterone Androgens and Competition Testosterone levels increase in anticipation of competition Androgens and Sexual Interest If in normal range testosterone levels don t predict sexual frequency Married men have lower testosterone than single divorced men Sex Differences in the Brain Male and female brains and nervous systems Sexually dimorphic structures Sexually dimorphic nucleus of the preoptic area Interstitial nuclei of the anterior hypothalamus Sexually dimorphic nucleus of the preoptic area SDN POA males females Interstitial nuclei of the anterior hypothalamus INAT males females female T females Androgens Masculinize the Brain Androgens play a direct role in the masculinization of the brain e g promoting a bigger SDN POA in male rats In many animals aromatization masculinizes the brain Testosterone is transformed into estradiol which produces masculinization Alpha fetoprotein binds estrogen and prevents maternal estradiol from masculinizing the female brain In most species mother s estradiol is blocked by the placenta Not in the spotted hyena OUTLINE Sexual Development Hormonal Effects on the Brain and Behavior Sexual Interest Orientation and Strategies Hormones and Sexual Interest Testosterone regulates sex drive in men an women Testosterone lower in older men those in long term relationships and following birth of baby Sexual Arousal Men Penile Tumescence Vaginal Moisture Women Sexual Arousal and Habituation Males habituate more to sexually arousing stimuli than females The Coolidge Effect The propensity of an animal that appears sexually satiated to resume sexual activity when provided with a novel partner Sexual Orientation Stable pattern of attraction to members of a particular sex Not synonymous with sexual behavior Males 96 98 heterosexual 2 4 homosexual Females 98 99 heterosexual 1 2 homosexual Brain Structure Sexual Orientation INAH 3 smaller among women and homosexual men than among heterosexual men Sexually dimorphic nucleus of the preoptic area SDN POA rats males females Insterstial nucleus of the hypothalamus INAH humans males females Spinal nucleus of the bulbocavernosus SNB rats males females Brain Anatomy and Sexual Orientation INAH 3 different between heterosexual and homosexual men 2 3X larger in heterosexual men than homosexual men Interpretation of findings limited INAH 3 is too small to observe in living participants studied autopsied brains Homosexual men identified by diagnosis of AIDS No one knows effect of AIDS on brain Genes and Sexual Orientation Unknown whether direct effect on orientation or indirect effect on prenatal androgen environment Hormones Sexual Orientation Development of structures not involved in sexual behavior often reflect the influence of prenatal androgen exposure in women Otoaccoustic emissions 2D 4D ratio Sexual Strategies Do males and females differ in their mate preferences and mating strategies Seeking sex with strangers Hormones and Sexual Strategy Oxytocin neurohormone secreted during child birth lactation promotes pairbonding Vasopressin neurohormone important for social behavior sexual motivation and pairbonding Anisogamy The sex with the larger gamete is the female Females begin with the bigger investment in the offspring Often especially in mammals females also continue with greater parental investment after the offspring is born Testicle Size in Primates Sperm competition The The midpiece of the the sperm sperm determines determines swimming swimming speed speed and and power power In In species species with with more promiscuous promiscuous mating mating strategies strategies both both the the testicles testicles and and the the sperm s sperm s midpiece midpiece are are larger larger Sexual Attraction The Importance of Symmetry Degree of similarity of one side of face or body to the other Sexual Attraction The Importance of Symmetry Degree of similarity of one side of face or body to the other The Beauty of Fertility and a Good Immune System Preference for younger features on female Preference for masculine men testosterone related facial features for casual sexual encounter less masculine men for long term partner Smell preference may indicate preference for an immune system different from our own e g MHC genes