**Friday's Urban Legend: DEFINITELY FALSE**

This month's issue of

*Scientific American*addresses this popular myth [Fact or Fiction?: Living People Outnumber the Dead].

The data is supplied by Carl Haub, an expect on world demographics at the Population Reference Bureau in Washington DC (USA) [How Many People Have Ever Lived on Earth?].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.

The myth isn't as outlandish as it seems. If you look at the chart above it's not difficult to imagine that the area under the curve from 1950 - 1998 might be close to the area under the rest of the curve. (The start point—Adam & Eve in 5,000 BC is meant as a joke.) Nevertheless, Carl Haub points out that it just doesn't make sense once you start to think about it seriously. But, and this is a serious "but", nobody really knows how many people were alive in the past.

The guesstimate begins with a decision about when to start counting. Haub picks 50,000 BC as a somewhat arbitrary beginning of the human population. As it turns out, the exact start point may not matter very much since the human population was probably small for many tens of thousands of years.Any such exercise can be only a highly speculative enterprise, to be undertaken with far less seriousness than most demographic inquiries. Nonetheless, it is a somewhat intriguing idea that can be approached on at least a semi-scientific basis.

And semi-scientific it must be, because there are, of course, absolutely no demographic data available for 99 percent of the span of the human stay on Earth. Still, with some speculation concerning prehistoric populations, we can at least approach a guesstimate of this elusive number.

The growth in human population can only be estimated by making guesses about the average life expectancy and birth rate at different points in time. Carl Haub is about as knowledgeable in this field as anyone so we can assume that his guesstimate is as good as it gets. Remember that we are interested in how many people have ever lived and this has to include children who died young as well as adults who lived to be 40 or 50 years old.

There are estimates of the number of people alive in 1AD based on the population of the Roman Empire and China. The consensus is about 300 million (45 million in the Roman Empire). By 1650 the world's population may have been close to 500 million even when you take into account the ravages of the Black Death.

Here's the bottom line. The people alive today represent about 6% of all the people who have ever lived.

A little cautionary tale in How to Lie with Statistics (there is a book by that title), though probably inadvertently.

ReplyDeleteThe graph looks like a sum from point to point, when each entry is actually a sample at each point, there is a difference...

Yes, I know. It should be a histogram. The difference isn't very important in this case.

ReplyDeleteIs #1,000,000,000,000 still alive? Where does she/he live?

ReplyDeleteMartin Hafner asks,

ReplyDeleteIs #1,000,000,000,000 still alive? Where does she/he live?She lives in that big house over on 5th avenue.