Ok I know this is going to rub a few people the wrong way but it's my opinion and I feel it's logically sound. and since you brought it up I will comment.
Most likely they will. People have actually over breed and have started to choke off life in other areas which in turn is creating an imbalance in the eco system. Also way too many people causes far more pollution than the earth can handle (thus the 6 degrees).
Much like a fish tank. If you let your fish breed and breed and breed and keep saving the lives of the weaker ones allowing them to live longer etc etc etc your system will eventually have way too many fish than it can support and it will crash and with that, almost everything in it will die. If you are luck a few will survive to continue the cycle again.
That is natures cycle. There is no stopping it. What we have succeeded in doing (Humans) is accelerate this cycle. We see it all the time in our tanks yet it amazes me how most people cannot grasp such a simple yet complex concept.
Ok I'm done <Soap Box Off>