Children of Men

There's a new Clive Owen movie out called Children of Men. It's based on the book by P.D. James, and although the two have little else in common, they do share the same basic premise: humankind suddenly becomes infertile and is faced with its own slow, inevitable extinction.

According to United Nations forecasts, humans will face a declining birth rate over the next few decades: after all, if fertility levels were to remain unchanged at today's levels, world population would rise to 244 billion by 2150 and 134 trillion by 2300. Clearly, current levels of high fertility cannot continue indefinitely.

The U.N. projects instead that global population will rise until about 2050, peak, and then decline slightly between 2050 and 2300. Whether Planet Earth will peak at a population of 8, 9 or 11 billion people will depend on "the choices that today's generation of young people aged 15-24 years make about the size and spacing of their families."

World Population Distribution, 1 AD
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World Population Distribution, 1960

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World Population Distribution, 2300
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Source: World Mapper.

As these maps show, population distribution has remained relatively consistent over the last two millenia, (accounting for the colonization of the Americas), and shall remain so into the future. According to this U.N. report, the greatest long term population growth is predicted for Africa, in both relative and absolute terms. Other regions' populations are predicted to stay level or decline.

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Did Japan really have 80% of the US population in 1960? These maps do not look even close to accurate. I also think the population of the Americas is grossly underestimated for 1 AD. Look at the book 1491 for the controversy on that.

I can't say that I am terribly worried about exponential population growth because there is really no evidence that exponential population growth ever occurs. Either exponential growth is retarded by high mortality rate or the birth rate falls because of economic progress.

The paradoxical effect of societies becoming richer is that they have less children rather than more. This is why Paul Ehrlich's Population Bomb proved to be fatally wrong.

People in rich societies choose to have 2 or fewer rather than 10 children because infant mortality falls, and there is no reason to have more. Therefore, if you want to cut the world population the most effective way to do so is economic growth.

Japan's 1960 population was about 52% of the U.S.'s: 94 million compared the U.S.'s 180 million.

As for the population of the pre-Columbian Americas, you raise a good point. The data source for the first map is Angus Maddison (2003), a population estimate that is part of
his series of historical statistics on the world economy. You can see the data from which the map was derived here, and read more about his research here. To summarize, it looks like he estimates the population of the pre-Columbian Americas at about 6 million people.

Most estimates for the population of the pre-Columbian Americas are much higher. I found figures ranging from 10 million to 200 million people--a few orders of magnitude's difference. As for the Charles Mann book you reference, I read an interview with Mann and he has this to say:

The population estimates when I was going to school were that the entire population of the Americas north of the Rio Grande was something on the order of 900,000 people and then there were a few million more people south of the Rio Grande.

And now a conservative estimate would be twenty to forty million, and I've seen estimates of up to 200 million. So if you do this kind of crude split the difference kind of thing, you end up with eighty to one hundred million, which was roughly the population of Europe at the time.

So, in answer to your second criticism, I have to agree: the population of Americas in 1 AD is probably grossly under-represented.