I don’t know if you’ve noticed, but if you are talking about 10 women, you use ellas, the feminine pronoun, but if you’re talking about 9 women and one man, you’d use the masculine pronoun ellos. I think this is best illustrated. OK, I’m back 20 minutes later with my work of art.

I don’t know all of the history of this phenomenon, but it obviously must derive from Latin. It’s also a hard call to say that the use of ellos is really gender discrimination against women, or if “ellos” is actually a gender-neutral pronoun applicable to mixed groups, and there is no “masculine only” pronoun. If this is the case, then it might be discrimination against men. Women have their own pronoun, but men don’t.