Genetically speaking, identical twins ought to be two copies of the same person. Environmentally speaking, if the twins grow up together, they ought to even be influenced by the same things. But if you actually pay attention to identical twins, they aren't identical in personality or interests. How do naturally occurring clones become individual people? That's the subject of a mouse study that Scicurious writes about on her blog. Fascinating stuff.
A review analysis of 13 studies — encompassing more than 13,000 individuals — found that there were more differences in personality, behavior, and preferences from one woman to another woman, and one man to another man, than there were between men and women as groups. In other words: The opposite sex isn't an alien life form. Men and women are both from Earth, not Mars or Venus. Diversity abounds, but you can't really classify those differences as "women are like this" and "men are like that". Instead, it's more like "this person is like this" and "that other person is like that".