Okay, I'll try again, because I'm stubborn, I've had a coupla glasses of wine, and (sadly) I've nothing better to do on Friday night. Social scientists distinguish between sex (the biological distinction you valorize) and gender (socially created, enforced, and enacted roles). For instance, I agree that the capacity to bear a child is a sex difference; however, the assumption that women will take care of elderly relatives or men are good at math is a gender difference. The point social scientists stress is this: no matter what the sex differences between men and women, they cannot explain the gender differences, because the gender differences are socially produced. With adequate control over social structure, socialization, and everyday social interactions, I could create a society in which women excel at math, men do the laundry, and so on.
There are few necessary linkages between sex differences and the social roles "men" and "women". Time and time again, enthusiasts of biological explanations like you have insisted that men are like this and women are like that because it's a sex difference (XX and XY and all that), and time and time again, it's been demonstrated that what was confidently presented as a sex difference is in fact a gender difference created and enforced through social relations.
For instance: the male-female gap in math performance. Fifty years ago in the U. S., men massively outperformed women on tests of math aptitude. At that time, the most common explanation among educational psychologists was that this is a clear sex difference: women's brains must not be capable of mastering algebra and calculus. Today, women in college math classes outperform men! Given the fact that the biological characteristics of men and women in the U. S. have not changed in any meaningful way in the past 50 years, we know that the huge gap in math ability 50 years ago was a gender difference, not a sex difference. --In fact, it's quite obvious: women then did not take as many math courses as men, so of course they performed worse on the tests! Today,
women are required to take about as many math courses as men do in high school and college, and the gender gap has more or less disappeared.
Does this clarify the usefulness of distinguishing sex differences and gender differences?
Miles