By looking at anthropological findings in tribal societies, sociologists can see fluidity in gender, which us see that the boundaries within our own system of gender: are emotionally guided. are biologically fixed. are psychologically established. may not be stable.

I believe the answer is: May not be stable
For example, when we observe the nordic culture, we could easily see that the role of men and women in that society tend to be enter twined with one another.
As our economy become more modernized, job opportunities that are less physically demanding started to arise and give women a huge opportunities to advance.