I know you are familiar with the taijitu - the Yin/Yang symbol. In it we see that the black segment has a dot of white and the white segment has a black dot - and that both of those aspects are needed in order to create wholeness. This is how I see Yin and Yang. Everyone has aspects of both and both are necessary in order to create wholeness. Someone who is all Yang is out of balance. Same goes for someone who is all Yin.

On a practical level, if Paleolithic peoples had very separate but complimentary skills/roles, human beings would have died out just like all other hominids other than humans did. If you had to rely on someone else who had skills and "nature" that was separate but complimentary to yours, it would be incredibly mal-adaptive. What is much more adaptive is that everyone has similar skills and abilities, even if there are times when you split the work in order to make sure that everything gets done (something that most anthropologists agree is the origin of gender work roles). After all, in some Native American tribes, men do the weaving, and in some, women do the weaving. Who is inherently or biologically "designed" for weaving? In Australian Aboriginals, often men go off and do religious ceremonies and such that women are not included in. While they are away, the men do all the regular "female" things and back home, the women do all the regular "male" things because splitting work has very little to do with actual "nature" or capability. It's just simply a way to split work in a practical way to make sure it all gets accomplished.