106,456,367,669 humans had been born, as of 2002

Google Books' census of books of the world (see this post) reminds me of palaeodemographers' commendable effort at finding an answer to the question, "How many people have ever lived on Earth?"

Carl Haub in 2002 provided an answer: 106,456,367,669 humans had been born, as of 2002(mid 2002?). Of course Haub understands the false precision associated with twelve significant digits in the number 106,456,367,669. It is entirely my fault for citing it. 

For getting an order-of-magnitude estimate, Haub's effort is invaluable. Human life expectancy was only about 10 years throughout most of the last 50,000 years. Infant mortality (by age one) was estimated at 40%. 

For a ballpark figure, assume that the median life span of the 106.5 billion people ever born is 10 years. So 53.25 billion people lived/live beyond 10 years of age. 

A tiny proportion of them would have been sufficiently literate to read. Ten years might have been close to the age of first reading of a book. (Who can tell?)  Assume 10% literacy among those aged ten or above (a very high estimate) and that literate people (living beyond 10 years)  have 40 reading years  (another high estimate). Then there are 213 (=5.325*40)  billion literate-man-years.

Google's figure of 130 million (129,864,880) book titles produced for 213 billion literate-man-years means 1638  literate-man-years per title.

Using this ratio, yearly publication of 289,729 new titles in the Anglosphere (see my previous post) would suggest a literate population of 474.6 millions (289,729* 1638) in the Anglosphere. Considering the vast army of English language learners in the world, and the changes in reading culture and publishing through history, this calculation yields reasonable ballpark figures.

Contrary to my initial suspicion, neither 106.5 billion people nor 130 million books seem unreasonable.