Maybe gender if just sensitive to an external influences...Not highly sensitive perhaps, but somewhere around the middle-of-the-continuum or right-side-of-the-continuum sensitive.
Maybe this saying is apt in the context of our recent past, because life forced us to adopt feminine and masculine traits that were more demarcated. To survive, men had to hunt, farm, provide food because women had to rear the young. The OP reflects the expression of these traits that manifested in our existence thus far, mainly for the most efficient, but also the most satisfying, survival.
Now technology surrounding eating and working and living makes it so strong traditional psychosexual traits aren't so necessary, and we are not only seeing more tolerance of sexual identity, but slowly, more gender bending (or maybe 'swaying' is more apt still) as well, into more open sexuality and androgyny.
I see this in my kids' generation regarding sexual and gender tolerance and expression, especially compared to our parents' generation. Quite a LOT of change actually, over a short period of time. But sexual fluidity (as in sex) seems to be more flexible than gender fluidity. Don't you think? I guess because male/femaleness is more primitive/innate in us than our sexuality. ?