90% of those who ever lived, alive today…?

A visitor to my World Population page in Interactive Mathematics questioned the line:

The frightening thing is that around 90% of all the people who have ever lived on the earth are alive today.

Huw said:

A simple calulation using the figures on your graphic shows that this can't be true.
1900 - 1.7billion
2006 - 6.6billion
So the 1900 population was around 25% of the current figure, and hardly any of those are alive today, right?
And of course that figure (25%) doesn't include all the people who lived before 1900. So where does the 90% figure you quote come from?

Hmmm - ya got me there. I cannot remember the source of this quote (yeh, I know - I should have correctly cited my source. Guilty as charged.) So I did a poke around and found the following from Caltech University which adds some light:

It may still be true that 90% of all the scientists who have ever lived are alive today, and that statement has been true at any given time for nearly 300 years. But it cannot go on being true for very much longer. Even with the huge increase in world population in this century, only about one-twentieth of all the people who have ever lived are alive today. It is a simple mathematical fact that if scientists keep multiplying faster than people, there will soon be more scientists than there are people. That seems very unlikely to happen.

Then there is this from World Population Awareness, which has a 5.8% figure, agreeing fairly closely with the Caltech opinion:

World Population: How Many Have Ever Lived.

An unknown writer claimed that "three-quarters of all the people who have ever been born are alive today". That erroneous statistic became accepted as fact. However, there is enough information to make a good guess as to how many people have ever lived on Earth. According to calculations a total of 106.4 billion people since man appeared about 50,000 B.C. That means that 5.8% of all the people who have ever been born are alive today.

Every year, global population increases by about 78 million people. It is estimated that humanity is consuming the earth's resources 20% faster than they can be sustained. Until the modern era, world population grew slowly. During the next eight milleniums, population grew at .05% per year, reaching 300 million in 1 A.D. During the following 16 centuries, the annual growth rate fluctuated, partly because of the Black Death, which ravaged 14th century Europe.

Today, there are six times as many people alive as at the start of the industrial revolution, 13 times more than when Columbus set sail and 20 times more than during the Roman Empire. There's an assumption that in pre- history women had as many babies as they could, so the birth rate would have been fairly high. Average life expectancy in Iron Age France have been pegged at only 10 or 12 years. There is considerable debate about when the human race actually came into existence.
December 23, 2002 Scripps Howard News Service 005096

I have updated the original article in Interactive Mathematics. Thanks, Huw for the question.

Footnote: 11th Jul is World Population Day.

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