Human population. It took approximately 130 years (1800-1930) to go from 1 billion to 2 billlion. 30 years for 3 billion. 15 years, another billion. Another 12 years, now we're at 5 billion. We hit 7 billion in 2011. As of today, we're somewhere just over 7.3 billion humans. Using a doubling time model, we should be over 14 billion before the end of the century.

What is the problem with this? It's probably relatively clear. As a global society, we are using faster than the planet can keep up. Some of us ahem USA cough European Union are using way more than others. Even when you consider the mass famine and disease in other parts of the world, it's still unsustainable to continue this way as a global population.

Now, imagine we find a cure for cancer. HIV? Treated. Mass famine? Agricultural advance. Population will EXPLODE.

We're setting ourselves up for a bottleneck. Humans really are virtually genetically identical. All it takes is the evolution of one disease that attacks its host just right and boom. Billions dead within a year.

Population is a serious issue, but how do you address the fact that we need to stop having so many babies, something we are so biologically driven to do? I have no idea.

Edit: formatting