Hormones Sexual Development Orientation A hormone is a chemical that is excreted by an endocrine gland it s conveyed by the blood to other organs whose activities it influences Many hormones have more than one target and more than one action There are different classes of hormones The class of steroid hormones are what we re talking about today Steroid hormones have 4 carbon rings in the internal receptors 6 hormones classified into two primary classes androgens testosterone for example estrogens primary estrogen is estrodial estrogens are a class of hormones Typically people think of androgens as male hormones and estrogens as female hormones This is a misnomer both sexes have them it s just the amounts that vary These hormones affect the brain and other organs Some of these hormones activate what are known as sex limited genes which means their effect is much stronger in one sex than the other androgens on males than females Sex hormones have both organizing and activating effects Organizing effects of these hormones occurs way before birth They determine whether or not the brain and body will develop male or female characteristics The activating effects occur well after birth like during puberty Female has 2 X chromosomes Male has an X and a Y chromosome Very early in fetal development both males and females have a set of Mullerian ducts and a set of woiffian ducts as well as primitive sex organs Male is the XY on the Y chromosome one finds the SRYG which causes the primitive sex organs to develop into testes The testes then start to produce that androgen testosterone which is in a sense self promoting because it feedbacks and enhances all that promotion The woiffian ducts differentiate into the seminal vesicles and the vas deferens Also see the secretion of another chemical MIH I stands for inhibiting which causes the degeneration of the Mullerian ducts Because females don t have the SRYG their sex organs develop into ovaries These ovaries produce estrogen The woiffian ducts degenerate hormone causing this hasn t been found and the Mullerian ducts develop into the uterus and the upper vagina All this happens during a so called sensitive period month 3 to month 4 pregnancy in humans Really depends on whether or not testosterone is around A high level of testosterone is going to cause that fetus to develop male characteristics A very low of level of testosterone equals female characteristics General statement is female is nature s default But it s too general of a statement Estrogen and testosterone BOTH are needed Alpha fetoprotein in rodents binds with estrodial and prevents it from entering cells where it could produce masculinizing effects Present in immature mammals not adults In addition to seeing effects on sexual organs you also see effects on brain like in hypothalamus In hypothalamus one will find the sexually dimorphic nucleus It s larger in males than females and it contributes to male sexual behavior The female hypothalamus produces the typical pattern of firing that will become important later on when menstruation begins Author tries to determine whether toy selection is an innate preference for sex It s impossible to determine this for certain Activating effects are not all sex related Testosterone and very lightly estrodial may decrease pain and anxiety they increase memory It s been shown that estrogen will increase nucleus branching in the hippocampus which is important for memory It s true that testosterone leads to an increase in sexual arousal in males and probably females as well There s increased arousal in females immediately pre ovulation when estrodial levels are high Another hormone indirectly related to sex is oxytocin It s important for pair bonding also referred to as social hormone It s released in orgasm in males and females It stimulates contractions when a woman goes into labor and it causes the mammary glands to produce breast milk The only parental behavior that is hormonally dependent at all in humans is oxytocin as it s responsible for milk production Some species typically amphibians have the ability to literally change sex If one sex is scarce they change sex so as to continue to reproduce Biological sex is being talked about not gender Gender identity is something that is solely human gender identity is related to gender roles This is what we expect of a particular sex This is completely dependent on culture Most people not all acquire a gender identity that matches their external sexual appearance And once again hormones are a big part of this Some individuals may be born with external genitalia that really are somewhere between a male or a female this can be due to one of a million different reasons Maybe there s a transposition of genes or the SRYG mutated in some way or maybe the hormones in utero are atypical A fairly common cause of this in females is a condition called CAH CAH leads to excessive testosterone being excreted and this results in a somewhat external male appearance Any individual with external genitalia that are ambiguous are referred to as intersex individuals A long time ago if an intersex individual was born there was the need for something to be done immediately 99 of the time the child was given the appearance of a female but that was only external Now that we know about hormones and chromosomes the best advice parents are given is to wait for the child to be old enough to tell them Another hormonal oddity that can occur is there are some individuals with an XY chromosome pattern who are insensitive to all androgens It s a condition known as androgen insensitivity Outwardly they have the appearance of a female external genitalia is female In puberty they have breast development But they never menstruate They have internal testes not a uterus they re infertile All of these individuals have a complete female gender identity because all they ve been exposed to is estrogens Whatever your orientation is one is pretty sure you were born with it Homosexuality is a preference for same sex partners heterosexuality is a preference for a different sex partner These exist in nature animal species are homosexual and heterosexual Most of what we know about biological basis of homosexuality is in men because men have been studied more than lesbians Evidence is overwhelming for a biological basis If you are a monozygotic twin of a gay male one has about a 30 chance of being gay as well If one is a dizygotic twin to a gay male