Cole Porter reminded us "Birds do it. Bees do it..." and even educated humans do it. Reproduction is one of the animal world's most basic functions. But with the current world population hovering just north of 6 billion people, many wonder if couples worldwide shouldn't be putting on the reproductive brakes.

During the twentieth century, the world population grew from 1.65 billion to its current level of over 6.3 billion people. Almost 80 percent of that increase occurred since 1950. It took just the 12 years between 1987 and 1999 for the world to add its most recent billion inhabitants -- the shortest period of time in history for that kind of population jump. And according to demographers, every second of every day, two people die and five are born.

Anxiety about overpopulation "officially" began as early as 1798 when the British economist and parson Thomas Malthus wrote An Essay on the Principle of Population. He argued that, "Population, when unchecked, increases in a geometrical ratio," and concluded that unless family size was regulated, famine would become a global epidemic. He believed that poverty and famine were natural outcomes of population growth.

In the book The Population Bomb, published in 1968, Paul Ehrlich carried the torch of fear of population growth. As Charles Mann wrote in The Atlantic Monthly, The Population Bomb was a "gloomy book for a gloomy time" that predicted unprecedented suffering due to the population explosion. In 1972, MIT researchers used computer modeling to predict that the world would exhaust its supplies of gold in 1981, oil in 1992, and farmland in 2000. Their report The Limits of Growth foresaw the collapse of civilization by 2070. And the book Famine 1975! warned that hunger would cause the complete demise of the Third World that year.

But those dire predictions did not come to fruition. As Stephen Moore wrote in The Washington Times, "These days almost no sane person gives any credence to the population bomb hysteria that was all the rage in the 1960s and 1970s."

Paul Ehrlich and others now estimate that humans actually occupy no more than one to three percent of the earth's land surface, prompting some to say that there's plenty of room -- and plenty of resources -- for everyone. Demographers assert that the world population will most likely peak in 30 years, then actually begin to decline. Global population is expected to be around eight billion in 2050, with a decrease to 6.4 billion by 2150.

Bill McKibben, former staff writer for The New Yorker and author of numerous books on the environment and society, isn't quite ready to celebrate. "The good news is that we won't grow forever. The bad news is that there are six billion of us already, a number the world strains to support. One more near-doubling -- four or five billion more people -- will nearly double that strain. Will these be the five billion straws that break the camel's back?"

But others assert that humans adapt both themselves and their environments to change. Ansley Coale of Princeton University said he doesn't see the wisdom in assuming worst case scenarios. "If you had asked someone in 1890 about today's population," Coale explained, "he'd say, 'There's no way the United States can support two hundred and fifty million people. Where are they going to pasture all their horses?'"

Think you know where you stand on this issue? During the course of this activity, we will ask you four more times: Should couples consider global population issues before having more than one child? Based on your responses, we will argue the opposite points of view. Only your final vote will count toward the results of this poll.