It was not natural.. it was created by Brahmins to oppress the so called "lower caste's." The interpretation of Varna's was falsified due to greed and hatred.. it was not meant to be discriminated upon.
Varna is not natural.. a person does not belong to a pre-defined Varna. He is never born in a Varna... as I posted earlier.. how could a son of a fisherman become "Veda" Vyasa and go on to write Mahabharata? How can a thief and a robber by profession "Valmiki".. write Ramayana?
There were many instances of women reciting Veda's.. why were they forbidden from doing so later on?
You are confusing jati and varna. The two are NOT the same and cannot be used interchangeably.
Varna is based on karma.. which determines your birth at a certain place, time, and surrounding. Jati is occupation-based.. that is why there is fluidity in jati, but not varna.. at least, not in a single lifetime.
And, you are parroting some nonsense about caste being "created by Brahmins to oppress" others.. that is some western interpretation of it.. if you get an untouchable (westerner) to interpret caste, that is all you're going to see..
And, all those instances you quote are EXCEPTIONS, not the rule.. yes women recited the Vedas.. Vyas was a fisherman.. Valmiki was a hunter etc. etc.. however, conversely, Drona was a Brahmin.. he engaged in warfare.. Sri Krishna never calls him a Kshatriya.. why? He was born a Brahmin.. don't confuse varna and jati.. two entirely different things..