Key takeaway 1 : There are different "stages" of sex differentation

There is chromosomal, gonadal and eventually hormonal sex.

It's not because you have a Y chromosome that you are a male. Altough Y chromosome features feminization inhibition genes and testes formation genes. So transition from chromosomal sex to gonadal sex occurs quite early during the development of the fetus.

Now, placenta is itself an endocrine organ and can impact the fetus sex differentation. For example, if the mother has a cancer or some sort of issue, the placenta can produce testosterone and will induce masculinization of some aspects of the fetus.

And eventually there is hormonal sex (or morphological sex) which is induced by steroid hormones i.e. estrogen and testosterone (impacts shape, jaw, …)

Key takeaway 2 : Testosterone does not drive penis development

Dihydrotestosterone drives penis development. And this is a significant difference because dihydrotestosterone is derived from testosterone because of an enzyme called five alpha reductase. And in some cases, babies (it's very rare) have a mutation where they lack this enzyme. So they are born without a visible penis and are treated as a girl until puberty hits and testorone levels begin increasing (produced by the testes that are up in the belly) and then a penis sprouts. It's called Guevedoces.

Key takeway 3 : Estrogen, NOT Testosterone, Masculinizes The Brain

Testosterone can be converted into estrogen by an enzyme called aromatase. And that's what can cause male breat tissue development. It's in fact known in athletes who take supraphysiological levels of testosterone for performance enhancements that they can convert (sometimes not always) part of that testosterone to estrogen. Such manly men.

And neurons in the brains secretes aromatase and therefore convert testosterone to estrogen in the brain. In other words, estrogen masculinizes the brain!

Key takeaway 4 : Hormonal impacts are not just about procuding one hormone. It's also having receptors able to sense it

Androgen insensitivity is a case where people are XY chromosomes so they are producing testosterones but they have a mutation so that the receptors supposed to sense testosterone can't.

And because of that, they have internal testes (they don't descend) and they look female. But they don't have ovaries, …

This illustrates the importance of not only producing a hormone but also being able to sense it. And this has some implications e.g. in performance enhancing drugs (SARMS for example).

Key takeaway 5 : Receptors causing baldness and beard growth

DHT receptors in the face promotes bear growth. DHT receptors in the scalp promotes hair loss. You can now imagine why some anti hair loss treatment have quite significant effects on other things because they impact important pathways for other things than hair loss.

And so this also tells that you can have a lot of testosterone/dihydrotestosterone (DHT) and still not grow a beard because you don't have the DHT receptors in your face.

Key takeaway 6 : Plants fight animals

It was demonstrated that plans can mimic estrogen or testorone properties through their pollen to influence animals populations that eat them in order to continue to flourish. Indeed by doing this they control the reproduction of their predators. So plants can push back against animals predators in very clever ways.

And now think about what humans are doing to the environment. And you don't think the environment is pushing back through some means we don't think about ?