can go only so far

It is this singleness of the playing field that reveals the inequality of the players. ... To a degree, also, environment promotes equality in its shaping of phenotypes. Various though we may be in our beginnings, we learn our lessons from the same master. Yet the shaping of muscles and manners and mind to uniform environmental demands can go only so far. Experience may fulfill or reduce the potentialities of the accidental egg, but it cannot create what was never there. And we cannot leave to our descendants the mind or muscle we have acquired in the exercises of survival; every egg comes fresh. - The Social Contract by Robert Ardrey

...

I have asserted that equality among sexually reproducing beings is a natural impossibility. I may assert with comparable force that in the history of vertebrate life, which has brought man to ascendancy, equality of opportunity is a natural law. It is opportunity suppressed not just by the totalitarian, but by the equalitarian as well.