Since when did people start thinking there are more than two genders? And why do they think that?

yes, there are more than 2 genders. if you see a picture of a girl, don't assume that is a girl because her inside may be a guy. U need to ask that person first. From now on we need to abandon words such as he she man woman boy girl male female because you may offend that person

Apparently since the dawn of humanity, and things were way more brutal back then. I heard rumors that back in ancient Egypt or maybe it was ancient Greece, a king or pharaoh it was common practice to cut off a man's dick and force them to live as a woman if they did an unspeakable crime most likely have intercourse with the queen. Castration was also supposably coming practice especially among monks. The idea of more than 2 genders didn't become popular/well known until maybe the 60s, and it's only become a popular topic since Bruce Jenner came out as "Caitlyn Jenner" in 2015.

If you educated your self on genders, you would know.