A notion representing a class of objects
If a group of objects is represented by one object of their class, this singular countable noun takes the definite article the. Its meaning is a notion representing a class of objects, not the only object or specific object. This function is called the generic function of the definite article. The definite article "the" in this function is used only with a singular noun, mostly with the names of animal species, plants, inventions, instruments, and some others. Ref Useful English
The woman has been marginalised throughout history?
I would suggest that Woman in this case is not per se a singular count noun its specialised as it can only refer to a singular. Where as Bear can be Bears and Elephants can be Elephants if there friends come round. A woman must become women or people if her mates drop in.
It is more common to see the plural form used in a case like this
Women have been marginalised throughout history?
But you are correct "The women" is not used and seem to have been relegated to use for television shows only. Why we use the plura form I have no idea maybe it a solidarity thing or maybe she just got tired marching through the millennia on her lonesome. I presume that when our language was formalised we did not, at that time, consider ourselves animals hence the missing "The"
The human began walking upright 6 million years ago
In this case the word choice is incorrect as much as I or anyone else wishes not to appear sexist. The correct choice should have been Man. Whilst it is quite acceptable to call either a bull or a cow an Elephant or a boar or a sow a Bear it. Unfortunately it no longer seems correct to call a woman a Man.
Man began walking upright 6 million years ago
But you are are correct we do not use The Man in this instance. Even if he considers himself a bit of an animal.
man noun (PEOPLE);the human race: C.E.D.