Biological Sex
Procreation
Fetal development
Birth and development
Puberty
Sexual Preference
Identity
Sperm Meets Egg, Chromosomal Sex, Gonadal Sex
Egg duplicates cells and they differentiate. Hormones come from mother and the developing fetus that organize and develop areas that will be masculinized or feminized.
XX or XY first, then gonadal sex (testes or ovaries).
Y Chromosome Inhibition of Feminization
Genes that have functions that suppress female reproductive organs (Mullerian inhibiting hormone). The SRY gene promotes the formation of testes and inhibit Mullerian ducts.
Males have wolffian ducts.
Placenta Is an Endocrine (Hormone-Producing) Organ, Adrenal Testosterone
The mother also has an adrenal gland that can produce testosterone. There are instances (say the other has a tumor) where too much testosterone is released with an XX chromosome fetus, masculinizing them (things like enlarged clitoris).
Hormonal Sex, Morphological Sex
The effects of the steroid hormones on morphological sex (shape of baby).
Hormones Fast & Slow, Sex Steroids Can Turn on Genes
Cortisol and adrenaline act quite fast. Adrenaline increases your heart rate. Cortisol acts a little slower but can still have fast effects.
Testosterone and estrogen (steroid hormones) can have quick effects through signaling. These lipophilic molecules (can pass through fatty membranes) can travel into cells and interact with DNA to change gene expression and function.
Long term effects are related to the genetic effects.
Primary Sexual Characteristics: DHT Drives Penis Development
You would think that it would be straight forward: Y chromosome suppresses the female reproductive pathway (Mullerian ducts), promote the development of testes, testes make testosterone, this organizes the brain to be male. Females instead have estrogen that makes their brain more feminine, etc.
In actual fact, there are primary sexual characteristics, which are the ones you are born with, and secondary sexual characteristics, which show up in puberty. These are happening in the brain, body, and spinal cord.
Primary: Testosterone is thought to be responsible for creating external genitalia. Not testosterone that is responsible for the penis in XY babies. It is actually a different androgen. Testosterone is converted in the fetus to dihydrotestosterone by an enzyme called 5-alpha-reductase. This is the dominant androgen in males. Responsible for aggression, muscular strength, beard growth, and male pattern baldness. It also determines the genitalia while the baby is still in the embryo.
Secondary Sexual Characteristics
The baby will then grow up and during puberty, release kisspeptin, causing the release of other hormones (GnRH, luteinizing hormone), stimulating the testes to produce testosterone. Testosterone stimulates the further growth of the penis, pubic hair, deep voice, etc. (Secondary characteristics).
Dihydrotestosterone = phenotype for primary sexual characteristics.
Testosterone = secondary sexual characteristics during puberty.
Penis Sprouting: Guevedoces
Genetic mutation where 5-alpha-reductase, which converts testosterone to dihydrotestosterone, doesn’t exist. The baby would look female, with no externally visible penis. After being raised as a girl, would grow a penis at 12 with the release of kisspeptin. Testes are not descended as a baby either.
Estrogen, NOT Testosterone, Masculinizes the Brain
The brain has receptors for testosterone and estrogen. Testosterone can be converted into estrogen by aromatase.
Estrogen Establishes “Masculine” Brain Circuits, Testosterone
Estrogen that is aromatized from testosterone sets up the masculine circuitry of the brain and testosterone is what controls the display of those behaviors later in life.
Breast Development in Males: Aromatase; Puberty, & Steroids in Athletes
Some testosterone gets converted into estrogen during puberty, resulting in breast bud development. Also shown in those who take exogenous testosterone. Aromatase is not just made in body fat. It is also made by neurons in the brain that convert the testosterone into estrogen, which masculinizes the XY individual.
Estrogen Powerfully Controls Brain Development in All Individuals
Androgen Insensitivity Syndrome: Hormones Need Receptors, SARMS
There are XY people who make testosterone, who have testes, no Mullerian ducts, and yet look completely female and feel female. The receptor for testosterone is mutated, so the testes never descend. Chromosomally male and testes are there but inside. A sign in them not menstruating around puberty. They can live normal lives as females but just can’t conceive. Don’t produce sperm at quantities that could do anything.
The testosterone can’t bind to receptors and have an effect on its target cells, suppressing the phenotypic masculinization.
SARMS can alter things more on the receptor side.
Cannabis, Alcohol: In Babies, Puberty & Adults
Cannabis promotes significant increases in aromatase activity. Increasing estrogenic activity. May promote breast growth. If estrogen is too low in males it can actually reduce libido though.
Smoking marijuana during pregnancy can shift the pattern of hormones in the developing fetus, such that it promotes more estrogenic outcomes, from increased circulating estrogen.
In females, the testosterone that comes from the adrenals has a powerful effect on libido and reproduction.
Drinking during puberty can increase estrogenic activity, affecting development.
Finger Length Ratios, Prenatal Hormone Exposure & Sexual Orientation
Young males tended to have auto acoustic emissions more often than females. People that self-report as lesbians self-report having these more too.
Gay men, on average, had higher testosterone.
Finger length ratios (averages) – D2 (index) to D4 (ring finger) digit ratio is greater in self-reported females than males. Particularly on the right hand.
Must be measured from the base of the finger to the tip to get a proper ratio. The more androgen you are exposed to in utero, the smaller the D2:D4 ratio. Meaning the ring finger tends to be slightly longer. Females usually have more equal length fingers.
Men who self-identify as homosexual tend to have a typical D2 to D4 ratio or hyper-masculinized. Self-reported lesbians tend to have smaller ratios too.
This measurement means it is completely divorced from behavior and hormone interactions. Androgen exposure in utero can have an effect on body plan and sexual preference separately.
Brain Dimorphisms with Sexual Orientation
In the brains of those who reported homosexual there is a difference in the interstitial nucleus of the anterior hypothalamus.
The D2 to D4 ratio is not a predictor of anything, just a window into possible androgen exposure early on. There are plenty of people who self-report as different to the expectation. 96% of people are heterosexual anyway so there is always that challenge with estimation (not causal).
“Older Brother Effects”: Male Fetuses Might Change Mothers & Subsequent Brothers
The probability of reporting as homosexual increases with each subsequent brother. There is a record in the mother that can feedback onto the genome for successive male children.
Estrogen and Testosterone: Sources, Levels & Ratios
Estrogen, testosterone, and their derivatives are sex steroids. Sex steroids are present in everyone but it is their ratio that demonstrates specific effects.
Pineal gland, hypothalamus, gonads (ovaries and testes), thyroid gland, etc., all make hormones. Ovaries for estrogen, testes for testosterone. Although, the adrenals can make testosterone too.
Enzymes can change chemical composition, such as aromatases. Mostly made from fat and in the testes (which can also manufacture estrogen).
Production of hormones varies throughout life. Prepubescent females produce very little estrogen (estradiol is the active form), during puberty they skyrocket, across lifespan it varies with the menstrual cycle, then drops at menopause. Testosterone in boys is low, then skyrockets at puberty, then drops at a rate of 1% per year. Although, some reports of men in their 90s with prepubescent levels.