This one should be a slam dunk. Unlike race, where the genetics and biology are, shall we say, fraught, I highly doubt anyone here will deny that genetics/biology plays at least some role in determining one’s gender. Likewise, is there anyone here who would deny that gender–what it means to be a man vs a woman–is influenced at least in part by the culture in which one is raised? Methinks gender roles are simply too variable–across both culture and time–to argue otherwise.
So while we could argue forever regarding the relative contributions of nature vs nurture in determining gender, I don’t think anyone could reasonably argue that both don’t play at least some role in its determination. (That said, reasonableness is at times in short supply, so…)