> Males have penises and females don't, does a scientific study need to be conducted to prove this point?

What you've described is what I refer to as "sex" while totally ignoring the topic of gender. https://en.wikipedia.org/wiki/Sex_and_gender_distinction

I'm not sure what your politics are, but a lot of people who have traveled down this path in a conversation ended up expressing very intolerant opinions towards transgendered people. If you do feel contempt for someone whose gender identity and/or assumed gender role doesn't match their biological sex, please don't share that opinion with me.