That video is full of so much cringe and retardation, I couldn't resist throwing a little shit on the parade. I'll counter it with an actual science lesson that's not made for adult children. And its about sex and gender, too! In fact, its on one of these people's favorite topics: Gender Identity as a Social Construct. You hear all of these ideas being tossed around, but you never really hear how they started or who started them or how they got to that conclusion. I'm going to tell you. And when I'm done, you'll know why people don't tell you its origins.
We're going to go back around the late-1950s to early-1970s. In this period, sex psychology was in vogue. Alfred Kinsey had laid the foundation and basically broke out all the taboos regarding it. So you had some really good studies, like Masters & Johnson. And then you have people like Dr. John Money. In 1965, twin boys went in for a routine circumcision. Unfortunately, it went bad for one of the boys, David. His penis was irrevocably damaged during the operation. Money was a prominent psychological researcher and he recommended to the parents to have the boy undergo a sex change, because he felt plastic surgery was not advanced enough at the time. Though, no one can be sure if plastic surgery could have helped. Because Money had a motive he hid from the boy's parents and he pushed the sex-change hard. This was because Money had a theory that Nurture was more important than Nature (an argument you hear a lot) in determining gender roles (Money is also responsible for the term gender role).
As to why this particular boy, the answer lies in the fact that they were twins. To those of you not familiar with research, twin studies are often the strongest because of genetic similarity, one serving as a perfect control of the other. To this day, twin studies are extremely strong evidence of something. Now, what happened was that the boy underwent the sex change. They removed his testicles and fashioned a vulva. He took hormone treatments and was raised as a girl. Neither the parents nor Money ever revealed the fact that he was actually a boy. The parents bought him dolls and dresses, the whole nine. But, here comes the kicker. The boy, now called Brenda, started to, well, act like a boy at the age of 7. Money did not like this. He forced 'Brenda' to realize that he was female. Not only that, in interviews later on he claimed the following:
He said as a child, Money forced him go "down on all fours" with his brother, Brian Reimer, "up behind his butt" with "his crotch against" his "buttocks", and that Money forced David to have his "legs spread" with Brian on top. Money also forced the children to take their "clothes off" and engage in "genital inspections". On at "least one occasion", Money reportedly took photographs of the two children doing these activities. Money's rationale for these various treatments was his belief that "childhood 'sexual rehearsal play'" was important for a "healthy adult gender identity"
Eventually, even with the hormones, without further reconstructive surgery puberty took hold and by 13, Brenda started acting more masculine. By 14, he was told the truth. He stopped the hormones, took back his name David and underwent reconstructive surgery to his penis. This story doesn't end there. Money never reported this. In fact, quite the opposite. He reported the experiment was a resounding success. Money lied to everyone's faces and his theories were taken up as fact. It was only 32 years later, in 1997, when the story came out in a rolling stone article. Nothing Money ever did worked. He ALWAYS felt male. Even though this research was touted as a success. This lead to thousands of infants being gender reassigned, who were intersex. Money was discredited, but he claimed that it was the evil 'anti-feminists' and 'right wing media' (If you consider Rolling Stone Right Wing) who did him in as a smear campaign.
This story doesn't have a happy ending. In 2000, Bruce, David's twin, committed suicide by overdosing on anti-depressants. In 2004, at the age of 38, David killed himself with a sawed-off shotgun blast to the head. So. Now you know where the 'science' of gender identity came from and perhaps the most unethical psychology study I've ever read.
There is something that can be learned from this, though. Money, for all his beliefs, proved the opposite of what he sought. There's more evidence for gender roles being Nature, rather than being Nurture. That experts, no matter how well-versed and respected, can still be predatory and blinded by their own personal biases. And that science isn't a religion, it isn't politics. Its fallible and the last thing it needs is people following their personal politics, going looking for things they already believe are true rather than just simply looking.