Peter Attia, M.D.

But anyway, with that as backdrop, how did you get interested in this topic?

Say more.

I want to go back to something you said a second ago, which is the distinction between mammals and non-mammals.

And I never really thought of it until you said this.

But if I were to look at a male great white shark and a female great white shark, first of all, do they have testosterone in them as the androgen or sex hormone?

Now, if you, again, go back to the example of great white sharks, typically the females are larger.

I would reckon they're just as aggressive as the males.

Is that reflected in comparable levels of testosterone in those species?

So just make sure I understand.

In the hyenas, if you took an adult male and an adult female hyena, would they have similar levels of testosterone and estrogen?

Despite the fact that phenotypically they look the same and they're both equally aggressive.

So the extent of my recollection from medical school on this topic was, and again, we can come back and talk about the edge cases, but 99.9% of cases are either XX or XY in terms of humans.

In humans, yes.

Yeah, right.

So we can talk about Turners and Klinefelters and things like that later.

But in the 99.9% of cases of XX and XY,

What are the steps and how do they involve sex hormones that create the phenotypic differences in the embryo?

Yes, yes, exactly.

I just want to start with, let's get through the first nine months and then let's help understand how those two options of chromosomes lead to two different body types.

Chromosomes are the sex hormones.