Based on what I've read, pre-agricultural people nursed their children until the age of 4 or 5 when they could keep up with the tribe on foot, which limited the birth rate. The explosive growth in population we have had for the last few thousand years dates to the agricultural revolution, when we settled down in one place which allowed women to wean their children sooner and have more. So in a sense the absence of birth control is the new and unusual phenomenon here. If you look at ratios of sexual activity to pregnancies human beings are extreme outliers- we clearly are evolved to use sex for bonding first and reproduction second, so the idea that birth control is going to change our behavior through selection pressure seems wrong.