Here is another, less talked about, but very unsettling sign of population overshoot: 27 million people are enslaved today worldwide -- more than at any time in history.

The most common form of slavery is debt bondage, in which a human being becomes collateral against a loan. With a massive population boom in regions of staggering poverty, some families have nothing to pledge for a loan but their own labor. With inflated interest rates, debts are often inherited, ensnaring generations. 15 to 20 million slaves are in debt bondage in Bangladesh, India, Nepal, and Pakistan.

Another common form of slavery is forced labor, where individuals are lured by the promise of a good job and instead find themselves enslaved. Migrant workers are particularly vulnerable, and small organized-crime rings fuel a booming international trade in human beings. Trafficking often flows from developing nations to the West. For instance, CIA estimates that 50,000 women and children are trafficked into the US each year as slaves.

A form of slavery most common in South Asia is sex slavery, where girls forced into prostitution by their own husbands, fathers, and brothers earn money for the men in the family to pay back local-money lenders. Others are lured by offers of good jobs and then beaten and forced to work in brothels.

Slave labor produces goods we use every day. Examples include: sugar from the Dominican Republic, chocolate from the Ivory Coast, paper clips from China, carpets from Nepal, and cigarettes from India.

Slavery occurs in every continent in the world except Antarctica.

To learn more about this, visit the American Anti-Slavery Group site.