The determining factor is the SRY gene. That's the element that triggers the developmental pathway. You are correct that the message has to be received as well - but the receptor isn't the trigger. It can also very rarely be translocated due to mutation. But at the end of the day, the SRY gene is what guides the fetus along the path of sexual differentiation.
You're saying it, but you're wrong.
Come to think of it, the situation would be even worse than that, since we would have defined sex-indicative features in a binary way (male/non-male) in order to make the bimodal plot work in the first place.
Nice to get some recognition and acknowledgement around this place ... 
Don't see that that necessarily follows. As I've indicated before, heights and personality traits are "sexually dimorphic" and it seems relatively easy to plot them to emphasize the bimodality in those traits:
There are probably dozens of definitions that have defined the sex categories, some that are more or less standard and well regarded by most biologists worth their salt. See:
. Many of them, like most of the transloonies, have turned the sexes into "immutable identities" based on some "mythic essences" instead of recognizing them as labels for transitory reproductive abilities.It might be splitting hairs, but I'm not sure that one can say that "sex" -- as a binary and nominal categorical variable -- is also bimodal:
www.statisticshowto.com
The standard biological definitions has it that some third of us are sexless. See Griffiths Aeon article:
aeon.co
Yes - Novella's take is pretty bad. He is blatantly ignoring the reason why female and male arose (i.e. to facilitate sexual reproduction). He tries to designate the brain as a sexual organ and again conflates clearly deleterious variation (DSDs) with benign variation. His example of complete androgen insensitivity syndrome (CAIS) people as not being male or female - we know they would be functional males if it were not for the mutations in the AR gene. It's again special pleading for one organ system (and species).To be honest, I think Novella seems to be doing some motte-and-bailley judging by his recent write-up of his talk at CSI-con. It would be good to see the actual video of the talk because Novella claims Coyne misunderstood his talk when he responded to it the next day in his own talk.
But Novella is being disingenuous is his own description of his talk is anything to go by. He argues that some DSDs are analogous to other biological difficulties of classification such as the archaeopteryx (is it a bird? Is it a therapod?) and he once, on the podcast rather fatuously said that the trans-rights people should adopt the platypus as their mascot (yeah, that will go down well, Steve!)
But as people here have noted, even if you could find a particular individual or pattern of development which defies easy classification, such people are almost entirely irrelevant to any policy debates and yet seems to be one of the prongs of the argument that policies should be reassessed.
A Discussion about Biological Sex - NeuroLogica Blog
At CSICON this year I gave talk about topics over which skeptics have and continue to disagree with each other. My core theme was that these are the topics we absolutely should be discussing with each other, especially at skeptical conferences. Nothing should be taboo or too controversial. We...theness.com
The following excerpt from a more-recent post of Jerry's might help clarify his views. Criticizing a paper in Science claiming that sex is "somewhat continuous," he wrote:That is the way I always think of it because I have never seen any reference to modes used in statistics except in relation to variables that can be ordered on the X axis. However, after reading Coynes piece a while back I looked into it and realised that categorical/nominal variables can also have modes. Since a mode is just the most frequent value it doesn't matter whether the frequency is a value on a continuous or categorical scale. For example, if I asked people for their favourite colour and got 45% red, 45% blue and 10% purple, I would technically have a bimodal variable. It's just isn't commonly encountered in that context because people are usually thinking of a peaks meaning smooth curves, which requires at least ordinal data on the X axis. (A bimodal nominal variable would also have peaks, but where they occur on the graph would be arbitrary and could not be fitted with a curve.)
"To be a bit more precise, biological sex in humans is bimodal: if you do a frequency plot with “sex” on the X axis and “frequency of individuals conforming to that sex” on the Y axis, you get a huge peak at “male”, another huge peak at “female”, and then a few tiny blips in between that conform to hermaphrodites or intersexes."
A defense of the binary in human sex
As a biologist, I get especially irked at the repeated claim that sex in humans is “a spectrum, not a binary.” In fact, as I’ve discussed several times before (e.g., here, here, h…whyevolutionistrue.com
whyevolutionistrue.com
Taking mode in the strict mathematical sense and taking "sex at birth" as a nominal distribution would result in a unimodal distribution, since most newborns are male. Once again, claims of bimodality just won't work.
Some my former Dev Bio colleagues (notably mostly female ones) would note at this point in the seminar that two X chromosomes are required for normal female development (and one X and one Y for normal male development).
I wonder if there is any similar topic where 99% of a thing is A or B and <1% is indeterminant and some folks say it's a spectrum or you can't quite tell which is which.The following excerpt from a more-recent post of Jerry's might help clarify his views. Criticizing a paper in Science claiming that sex is "somewhat continuous," he wrote:
The proportion of individuals who are either male or female, based having the developmental equipment for making big or small gametes, is not “somewhat continuous”. It is nearly completely binary, with only 0.018% of individuals (as the authors admit, about 1 in 5600—they say 2 in 10,000—being of indeterminate sex, including intersexes). That means that 99.982% of individuals lie in the two peaks, or rather two straight lines shooting upwards. This is not at all “somewhat continuous” it is all but binary with a teeny blip in the center. Call that “very very very very strongly bimodal” if you wish, but the proportion of indeterminate individuals is miniscule, and these individuals are not a third sex, but represent developmental anomalies. Essentialism is in effect the case here: there are only two sexes and a very few individuals of indeterminate sex.
Science, essentialism and the sex binary: an annoying new paper in Science
There are many things to criticize about this new paper in Science (one of three “woke” papers in the issue), but to me the worst is its denial of the sex binary. For that binary, whos…
Wow. And eye colour is categorical.
Yes, there are other genes involved in both male and female sex determination, e.g. the main function of SRY is to trigger SOX9 - the more conserved player in triggering male development. Indeed (as has been explained) there are many genes involved in every organ system. The underlying developmental complexity still results in two reproductive phenotypes (+2 eyes, a functioning liver, etc.).
And you claim to be formally trained as a biologist?
Sad to see that the once-respected Steven Novella has fallen into the trap of placing ideology ahead of objective, observable scientific truth.
Right? It's like they are trying to be fractally incorrect.
I'm going to take a crack at this since Bob D. evidently won't do so: HRT for CAIS.