When somebody says "the man determines the sex of the baby. you can't be trans because it doesn't exist. it's simple science you can't go against biology." this is what I tell them.
“You’re right, and you’re wrong. It’s actually not simple at all. On average, fertilization occurs about two weeks after your last menstrual period. When the sperm penetrates the egg, changes occur in the protein coating around it to prevent other sperm from entering. At the moment of fertilization, your baby’s genetic make-up is complete, including its sex.
If a Y sperm fertilizes the egg, your baby will be a boy; if an X sperm fertilizes the egg, your baby will be a girl. In that sense you are technically right, but gender is determined by so much more than that. We all know that a man’s brain is different to that of his female counterpart, right?” By which point the person who I’m talking to agrees. then I go on to say.
“In month 3 of Pregnancy
the baby has grown from embryo to fetus. by now the baby’s arms, hands, fingers, feet, and toes are fully formed. the baby can open and close its fists and mouth. Fingernails and toenails are beginning to develop and the external ears are formed. The beginnings of teeth are forming, and the baby’s reproductive organs are also developing, but the baby’s gender is difficult to distinguish on ultrasound, because the genitalia start out the same. Differentiation of the male and female reproductive systems does not occur until this crucial fetal period of development.
It is believed by scientists that during the intrauterine period the fetal brain develops in the male direction through a direct action of testosterone on the developing nerve cells, or in the female direction through the absence of this hormone surge. According to this concept, our gender identity (the conviction of belonging to the male or female gender) and sexual orientation should be programmed into our brain structures when we are still in the womb. However, since sexual differentiation of the genitals takes place in the beginning of the third trimester, (The third month of pregnancy) and sexual differentiation of the brain starts in the second half of pregnancy, these two processes can be influenced independently, which may result in trans-sexuality. This also means that in the event of ambiguous sex at birth, the degree of masculinization of the genitals may not reflect the degree of masculinization of the brain. There is no proof that social environment after birth has an effect on gender identity or sexual orientation. Data on genetic and hormone independent influence on gender identity are presently divergent and do not provide convincing information about the underlying etiology. To what extent fetal programming may determine sexual orientation is also a matter of discussion. A number of studies show patterns of sex atypical cerebral dimorphism in homosexual subjects. Although the crucial question, namely how such complex functions as sexual orientation and identity are processed in the brain remains unanswered, emerging data point at a key role of specific neuronal circuits involving the hypothalamus. So yes you are right, it is biology I’m not fighting anything other than ignorance.”