This needs to be carefully qualified. Infant mortality rates for the first 99% of human history were so shockingly, stupefyingly high, that a woman might only expect to have about three of her children survive to adulthood (and maternal mortality rates were also so high that a woman wouldn't expect to survive more childbirths than 5 or 6).

What this means is that the human population was only marginally above replacement for the majority of human history. Human population didn't explode until the medicinal revolution.