Human must be the favourite creation from the Nature. We are not only blessed with the power to think and comprehend but also very much suitable for the current situation. Human population grows tremendously in recent centuries especially after World War II (refer to http://en.wikipedia.org/wiki/Population_growth). Referring to the graph here, our population actually doubled from 1960s until now.
Once people thought we might experienced serious food crisis that will prevent the human to expand further however with the technology, we are able to produce food better for most of the people here (2 out of 7 billion people here still experiencing food security).
Can we keep populating the world more if we keep living longer, consuming the food and energy? There are signs we might hit the limit soon. With the growing competitiveness, some developed countries are experiencing lower birth rate.
I think we human are the greedy bunch. The mother earth has loved us so much, why are we keep taxing her? One day, the power of nature will strike us. :(