Yea, it's a cycle. There's actually a really cool theory on the "stages" of birth. How we progress and have more and more births until we begin to slow down at Stage 3, where we have begun to overpopulate. Stage 4 consists of numbers beginning to stabilize and decrease because of less relationships and sex protection. Stage 5 supposedly carries a plague that wipes out many, and restarts the cycle. We increase every time though, and eventually we'll overpopulate regardless.
It's just a theory, and I honestly don't agree with everything, but it's cool stuff.
Overpopulation is a delicate subject, but advancement and spread is an opportunity we should take.