Brute force. The social constructs that offset brute force are a luxury. When a group operates close to the margins they can't afford those luxuries. Therefore primitive human groups, just like other primate groups, would most likely operate by brute force and not social stratification.
Brute force is itself a luxury, in societies like this. You can't go clubbing everyone you disagree with when they represent a vital source of labour; start down that road, and soon half the tribe are dead from split skulls and the other half from starvation. Violence within the tribe is a last resort against extreme deviance, something when a member of the group becomes so problematic that his labour fails to offset his disruptiveness. It's more likely that, as Terx suggests, subtle distinctions in status were used to control newcomers, because these allow the group to hold a potentially disruptive newcomer at arm's length without either losing a significant amount of labour or introducing dynamics that would themselves prove disruptive.
The reason that warriors in, say, the Norse sagas are constantly slaughtering each other isn't because they were primitive, but on the contrary, a sign of their social complexity, because it indicated a society with enough of a material surplus to support not only a social structure that could spare a healthy adult male over some matter of pride, honour or ambition, but could support an entire social strata with nothing better to do than build elaborate rituals around their own material disposability. Hunter-gather societies, which live maybe a week from starvation in the best of times, don't have that kind of luxury.
You made the same mistake you always make - thinking that women are objects, instead of granting them personhood.
Looking at modern apes and most other pack animals, females show about the same sex drive that men show, there's absolutely no reason to assume that normal prehistorical sex was a "Men force themselves onto women, and women let them to it because they have no choice"-scenario, other than your ideological bias.
Eh, the dynamic isn't so much active men and passive women as active captors and passive captives, it's just that women are far more likely to be captives than men: adult men are much harder to integrate into a community than women and children, so it was more likely that they'd just be killed, while children are relatively easy to integrate so require no special status. Adult women are tricky because they're already fully-grown people with an established identities, and that throws up a particularly tricky dynamic. Indeed, leadership in navigating that identity was often taken up by the older women of a group; among the Eastern Woodlands Indians, it fell to the clan matrons to decide which captives would be adopted into the group, among which families the captives would be distributed, and to oversee the rituals of adoption.
I do agree that the active captor/passive captive dynamic is itself an over-simplification, and captives could certainly come to control their own destiny to a considerable extent, but we're essentially talking about Day One of their captivity, about how a group deals with newcomers, rather than the longer-term prospects for those newcomers.
