With the ability of man to think ahead and prepare against ever more of these decimating factors, he outsmarted the natural checks and started to isolate himself from the limits of growth. A simple example: the building of houses eliminated the dependence on scarce natural shelters like caves.
Unfortunately, with improving conditions the urge to multiply did not diminish. Lust and the desire for children are built into us like in every other creature, all for the sake of the species. And we do as nature commands ...
Of course we can't blame ourselves for trying to evade the seemingly cruel balance between giving birth and getting killed. But the problem is obvious: no more checks, no more balance.
There is only one thing that can stop the avalanche: the brain that allowed us to come this far. If there is no outside power to keep control over our sprawling, we have to do it ourselves.
Don't think we are targeting just the so called development countries. Of course, the rates of population growth there are generally higher than elsewhere; campaigns just like the ones against HIV/AIDS should spread the word and make the issue an urgent one.
But the industrial countries have to do their share; often whole economies are based on prospected growth of the number of citizens. Furthermore it is obvious that reducing birth rates in poor countries will only work if the well-being of parents is not dependent on a large number of children to support them. Massive support from wealthy countries is inevitable, in their very own interest.
Eventually, everyone of us should use the mind that allows us to do so many interesting and wonderful things, and think hard about personal consequences, especially when planning to laying the foundations for a new family. If we make decisions out of love - or out of our guts, to put it more pointedly - we must be aware that this is exactly the moment where the old urge prevails from times when lives were short and hardly any children survived.
Even when deciding in favour of having children, there is always the possibility of adoption. Or to have a single child.
If you have grown-up children, don't push them because you badly want grandchildren. Remember, this is the ancient urge at work, too.
All these steps - globally and personally - will interfere deeply with traditions and social structures, even with the image we have about ourselves. But the prospect of a global breakdown should be enough to accept this upheaval. And there is a good side of it, too!
We need to overcome the urge to multiply by treating it like other instincts that we don't follow instantly because there is no use - and no place - for them in a modern society (like grabbing and eating something in reach instantly, regardless of ownership). Again, this requires a fundamental re-evaluation of values and traditions. Not because belief and rituals are something bad in themselves, but because some of them could in all consequence be nails in the coffin of the human species as we know it.