The Science Of Sexual Development

Key Takeaways

• A hormone has to be able to bind the receptor and take action on target cells to be effective

• Testosterone and estrogen can travel into cells and interact with the DNA of cells to control gene expression

• Primary sexual characteristics show up at birth (external genitalia) while secondary sexual characteristics take place during puberty (deepening of the voice, hair growth, etc.)

• Masculinization of the brain in males and females is accomplished by estrogen via aromatase which converts testosterone to estrogen

• Estrogen sets up masculine circuitry in the brain, testosterone controls the display of behaviors

• In utero exposure to androgens may have an impact on mate selection and sexual orientation later in life

• Pre-conception and in utero exposure to certain substances can impact the sexual characteristics of the fetus

• The average density and volume of human sperm has decreased significantly in the U.S. and Europe

Hormone Overview And Development Of Fetus

• Definition of hormone: released in one area of the body (usually from a gland) that travel and have effects on that gland and other tissues in the body

• Hormones have direct effects on the brain, body, and spinal cord

• Androgen: category of hormones, including testosterone

• Chromosomal sex: in general – the XY chromosome is male and XX chromosome is female

• Y chromosome has genes that suppress female reproductive organs, promote the formation of testes, inhibit müllerian ducts

• The placenta itself is an endocrine organ

• Gonadal sex: in general – if gonads are testes then the fetus is male; if gonads are ovaries then the fetus is female

• Steroid sex: effect of steroid hormones (i.e., testosterone and estrogen) on traits such as the shape of the baby, human, genitalia, jaw

What Hormones Do

• The hormone has to be able to bind the receptor and take action on target cells to be effective

• Hormones have two categories of effects: fast and slow in terms of the effect on genes

• Fast-acting hormones: cortisol, adrenaline

• Slow-acting hormones: testosterone, estrogen – can signal and attach to a cell to induce quick effects but generally have long-term effects

• Testosterone and estrogen can travel into cells and interact with the DNA of cells to control gene expression

• Effects of hormones are seen in primary sexual characteristics (the ones you’re born with) and secondary sexual characteristics (show up in puberty)

Primary Sexual Characteristics In Males

• Primary sexual characteristics show up at birth – external genitalia which defines sex

• Enzyme dihydrotestosterone is actually what’s responsible for the development of the penis in baby’s that have an X and Y chromosome – not testosterone

• Dihydrotestosterone masculinizes primary sex characteristics

• The brain has receptors for testosterone and estrogen

• Masculinization of the brain is not accomplished by testosterone

• Masculinization of the brain is accomplished by estrogen, not testosterone – testosterone is converted to estrogen by an enzyme called aromatase (made by body fat and neurons in the brain)

• Estrogen sets up masculine circuitry in the brain, testosterone controls the display of behaviors later in life

Secondary Sexual Characteristics In Males

• Testosterone is involved in the development of secondary sexual characteristics – deepening of the voice, growth of pubic hair

• Dihydrotestosterone is responsible for facial hair but also lack of hair on the head

• Speed of entry and exit from puberty might be worthwhile to study correlation to aging and longevity arc

In-Utero Effects Of Hormones On Sexual Preference

• Study: young males (versus young females) have more auto-acoustic emissions as picked up by the device

• Females who identify as lesbians had comparable auto-acoustic emission to males

• In utero exposure to androgens may have an impact on sexual preference

• This type of study has been replicated approximately six times and has shown interesting correlations

• It’s possible the brain organizes early and impacts same- or the opposite- sex choices later in life

Environmental Factors In Sexual Characteristics

• Maternal use of evening primrose oil and skin contact with infant or young males accelerated breast bud development

• Primrose oil promoted estrogenic activity in the body

• Atrazine exposure in water causes severe testicular malformation in the organ

• Herbicides have negative effects by impacting the ratio of hormones in the mother or testes or father – and – direct effects altering fetus

• The average density and volume of human sperm has decreased significantly in the U.S. and Europe

Lifestyle Factors In Sexual Characteristics & Child Development

• THC and other things in cannabis promote significant activity in aromatase (which converts testosterone to estrogen)

• Pot smokers have a higher rate of development of gynecomastia (male development of breasts)

• Smoking marijuana during pregnancy can promote more circulating estrogen in the body of developing fetus

• No peer-reviewed, quality studies that cell phones are bad for the brain – but – there is evidence of defects in ovarian and testicular development

• Cell phone storage in males: chronic exposure to cell phone emitted waves on gonads could impact swimming speed and density, and testosterone levels

• Cell phone storage in females: chronic exposure to cell phone emitted waves can impact estrogenic levels and regularity of cycle, and prolactin levels

• Creatine promotes balding in some males because of its effects on dihydrotestosterone

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