The human population has swelled so much that people alive today outnumber all those who have ever lived, says a factoid whose roots stretch back to the 1970s. Some versions of this widely circulating rumor claim that 75 percent of all people ever born are currently alive. Yet, despite a quadrupling of the population in the past century, the number of people alive today is still dwarfed by the number of people who have ever lived.

In 2002 Carl Haub, a demographer at the Population Reference Bureau, a nongovernmental organization in Washington, D.C., updated his earlier estimate of the number of people that have ever existed. To calculate this, he studied the available population data to determine the human population growth rates during different historical periods, and used them to determine the number of people who have ever been born.

For most of history, the population grew slowly, if at all. According to the United Nations' Determinants and Consequences of Population Trends, the first Homo sapiens appeared around 50,000 years ago, though this figure is debatable. Little is known about this distant past and how many of us there might have been, but by the time of the agricultural revolution in the Middle East in 9000 B.C., Earth held an estimated five million people.

Between the rise of farming and the height of Roman rule,population growth was sluggish; at less than a tenth of a percent per year, it crawled to about 300 million by A.D. 1. Then the total fell as plagues wiped out large swathes of people. (The "black death" in the 14th century wiped out at least 75 million.) As a result, by 1650 the world population had only increased to about 500 million. By 1800, though, thanks to improved agriculture and sanitation, it doubled to more than one billion. And, in 2002 when Haub last made these calculations, the planet's population had exploded, reaching 6.2 billion.

To calculate how many people have ever lived, Haub followed a minimalist approach, beginning with two people in 50000 B.C.—his Adam and Eve. Then, using his historical growth rates and population benchmarks, he estimated that slightly over 106 billion people had ever been born. Of those, people alive today comprise only 6 percent, nowhere near 75 percent. "[It is] almost surely true people alive today are some small fraction of [all] people," says Joel Cohen, a professor of populations at the Rockefeller and Columbia Universities in New York City.

For this myth ever to be valid there would have to be more than 100 billion people living on Earth. "How cozy," Cohen says. "It just doesn't seem plausible," he adds.

Today there are more than 6.5 billion people walking on Earth, according to United Nations estimates. Recently, the population has been increasing by about 1.2 percent each year, down from the late 1960s peak of a 2.1 percent yearly growth rate. Some industrialized countries, especially France and Japan, have very low birth rates and their populations are actually dwindling, Haub notes. In developing nations populations continue to grow, but some countries, such as India, are experiencing a slowdown in their growth rate.

Cohen doubts that a doubling of today's population, to 13 billion, will occur, never mind approaching anywhere near 100 billion. Not even the U.N.'s highest projection predicts that much growth, he says. For 2050, the world body's estimates range from 7.3 billion to 10.7 billion people. The median, and most likely, projection of 8.9 billion relies on a gradual slowing of the growth rate. And the U.N. predicts the world population will stabilize at 10 billion inhabitants sometime after 2200. At this rate, the living will never outnumber the dead