COGNITIVE SCIENCE 17 Why Sex is Necessary Jaime A. Pineda, Ph.D. Part 1 Jaime A. Pineda, Ph.D.

Without these behaviors most species would not survive Why is Sex Necessary? Sexually dimorphic behaviors Anatomical, physiological, and behavioral differences between males and females of the same species. Courting Mating Parental behavior Aggressive behavior Without these behaviors most species would not survive

Is Sexual Identity Learned? The case of Bruce who became Brenda who became David Socialization over biology? XX (female) and XY (male) genes A person’s genetic sex is determined by the father SRY gene on short arm of Y chromosome- dictates the development of the fetal testis (testis-determining factor) and triggers action of receptors to receive chemical message hormone brings

Is Sexual Identity Learned? The Y chromosome controls the development of the glands that produce the male sex hormones The default sex (if the Y chromosome isn’t present or doesn’t work) is female

Initially, there are more males than females

Sexual Development Three categories of sex organs (primary sex characteristics) Gonads (testes or ovaries) Develop first (Sry  testes; otherwise ovaries) Produce ova/sperm and secret hormones Critical Period of sexual development: Gestational weeks 7-12 Internal sex organs External sex organs

Sexual Development Gonads can become either Testes or Ovaries Develop as a function of the presence or absence of SRY gene In males, at 7th week, outer portions of gonads degenerate and inner portions develop into testes In females, at 11th week, inner portions of gonads degenerate and outer portions develop into ovaries

Sexual Development Gonads become testes in males Testes - endocrine glands that produce • male hormones (androgens) • Mullerian Inhibiting Substance Most changes reflect the presence or absence of androgen

Sexual Development Gonads become ovaries in females Ovaries- endocrine glands that produce female hormones (e.g.estrogen)

Sexual Development Internal sex organ precursors Mullerian system  female Develops into fimbriae, fallopian tubes, uterus, and vagina Wolffian system  male Develops into epididymis, vas deferens, seminal vesicles Develop as a function of hormones released by testes Mullerian inhibiting hormone or anti Mullerian hormone(defeminizing effect) Androgens (masculinizing effect): testosterone/dihydrotestosterone

Sexual Development Wolffian Ducts - later become • epididymis • vas deferens • seminal vesicles Mullerian Ducts - later become • uterus • fallopian tubes • upper part of vagina

Sexual Development External sex organs Penis and scrotum in males Labia, clitoris, and outer vagina in females Female development is the default “Nature’s impulse is to create a female” Male development requires androgens

Undifferentiated External Genitalia (<7 weeks)

Partially differentiated external male & female genitalia

Fully developed male & female external genitalia

Fetal External Genitals: Female 11-12 weeks 19 weeks

Fetal External Genitals: Female 5 months

Fetal External Genitals: Male 15 weeks 16 weeks

Sexual Development Dysfunctions Androgen insensitivity syndrome Genetic mutation that prevents the formation of androgen receptors Gonads become testes (normal process) Defeminization (normal process) Lack of masculinization (abnormal process) An XY male with female external genitalia; have a woman’s body but not internal female sex organs

Sexual Development Dysfunctions Persistent Mullerian duct syndrome Failure to produce anti-Mullerian hormone Absence of receptors for this hormone In an XY male, defeminization does not occur but masculanization does Person is born with both sets of internal sex organs Turner’s syndrome Individuals have only one sex hormone: an X chromosome Essentially develop into females (normal internal/external sex organs) However, no ovaries since two XX chromosomes needed

PUBERTY - development of secondary sex characteristics Puberty occurs when hypothalamus begins to secrete gonadotropin-releasing hormones (GnRH) causing pituitary to release Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) In males, these hormones stimulate testes to produce sperms and secrete testosterone (androgens) In females, they stimulate the ovaries to produce estradiol (estrogens)

Puberty – cont. Nutrition affects age of puberty Reduced in developing countries Thin girls reach puberty later Due to the presence of leptin

Hypothalamus Anterior Pituitary Hormonal Changes in Puberty FSH- RF LH- RF Anterior Pituitary

Hypothalamus Anterior Pituitary Hormonal Changes in Puberty FSH- RF LH- RF Anterior Pituitary FSH FSH LH ICSH(LH) OVARIES TESTES

Hypothalamus Anterior Pituitary Hormonal Changes in Puberty Ovulation FSH- RF LH- RF Anterior Pituitary FSH FSH LH ICSH*(LH) TESTES OVARIES Ovulation Corpus Luteum Ovum Growth Testosterone Spermatogenesis Progesterone Estrogen (estradiol) * Interstitial-cell stimulating hormone

Sexual Maturation Secondary sex characteristics (onset of puberty) Females (estradiol) Enlarged breasts Growth of the lining of the uterus Widened hips Maturation of genitalia Females (androgens) Underarm and pubic hair (face as well) Males (androgens) Facial, underarm, and pubic hair Deep voice Alter hairline (baldness) Muscle development Males (estradiol)

Hormonal Control of Reproductive Cycle Menstrual cycle Begins with secretion of FSH to stimulate growth of ovarian follicles (epithelial cells surrounding each ovum) As ovarian follicles mature they secrete estradiol causing the growth of the lining of the uterus (preparation for fertilization) Increasing levels of estradiol triggers the release of LH causing ovulation (release of ovum) Ovum enters a Fallopian tube and starts migrating towards uterus. If it meets sperm and becomes fertilized it begins to divide and then attaches itself to uterus wall If it is not fertilized, the ruptured ovarian follicle (corpus luteum) and the lining of the uterine wall will be expelled – menstruation commences