-Metacelsus- t1_jad961c wrote on February 28, 2023 at 4:36 PM

Reply to comment by lazercheesecake in Why does temperature determine the sex of certain egg laying animals like crocodiles? by insink2300

> The gonads themselves react to the environment temperature epigenetically. This is the theory that is the biggest departure from the others as it doesn't specifically target a separate messenger hormone (even though one may or may not be present).

This has been proven pretty well, at least in one species of turtle: https://pubmed.ncbi.nlm.nih.gov/29748283/

But other species might be different.

Also, you write, "in humans, all babies start off development as females." But this isn't correct. A better way to say it would be that they start off as undifferentiated, and trigger male or female development depending on whether the SRY gene is present.

lazercheesecake t1_jadvkqt wrote on February 28, 2023 at 6:58 PM

That there is an epigenetic component is not what was contentious. My point being it is unknown which mechanism in the temperature-signal pathway is the root of TSD. KDM6B is proven to be a vital component in the epigenetic expression of DMRT1 but what triggers KDM6B? That is unexplained.

Also, I do admit "in humans, all babies start off development as females." is a bit of an exaggeration, but it is not incorrect. As seen in AIS individuals, as I highlighted in my post, without male differentiating hormones, human bodies, for the most part, develop phenotypically into female presenting bodies. So much so that prior to modern times and ready genotyping, the most common diagnoses of AIS occurred in mid to late puberty when the individual did not start menses or develop other secondary sex characteristics.

Many male organs are direct descendants/adaptations of female organs, the differentiation of which occurs only in the presence of male differentiation hormones.