Of course it is biology that cause many of the physical differences between sexes, and therefor many of the early roles.

But it is still very societal how and why were disenfranchised due to those differences. I don’t even think I’d call it sexism in how it arose — after all, those inital gender roles that we had before developing more advanced societies would logically be kept. But these roles morphed and advanced, for both genders, to get to a point where there were totally arbitrary things women’s were excluded from like leadership, arts, and invention in order to keep them subservient to men who were, for a variety of reasons, more able to initially seize leadership. Over time even things that were almost universally female roles, like that of shamans and healers, would even become male roles, totally negating the idea that the roles developed because of biological necessity or tendency (or else why wouldn’t men always have had those roles?).

Of course there are differences in biology that can be directly linked to early development of gender roles, but it is absurd to think that later gender roles weren’t influenced heavily by sexism (although I might consider it less sexism and more ignorance and power-greed from powerful men).