How a Population Ages or Grows Younger: Classic Ansley Coale paper finally updated

Earth as a ball of flesh expanding at the speed of light — where we were headed as of 1960 (DALL-E)

People who teach demography love their classic articles. That methods paper that talks about microfilm and floppy disks, the incredibly intricate dissection of changes in Census data from 1970 to 1980. dispute over life expectancy forecasts from the 1970s. There is a lot to learn in these papers, but students of today may be forgiven for rolling their eyes. Why doesn’t someone just update the damn things? (There are good textbooks, of course, but real seminars make students read this stuff in the original.)

As I prepare to teach Population and Society, our introductory demography seminar for graduate students, for the first time, I have inherited a fabulous syllabus from Feinian Chen with lots of great classic papers. One I would like the students to read is by Ansley Coale, from 1964: “How a Population Ages or Grows Younger.” It makes some key observations that are counterintuitive at first and serve as a great introduction to demographic thinking. Most important (according to him in this 1987 interview) is that reducing mortality in populations with high mortality often leads to a younger population — because more children survive. And then he explains that if we want to survive as a species (he was a little hung up on nuclear annihilation) we are going to have to reduce fertility rates drastically, or else live with very high mortality rates. Fortunately, that’s what we’re doing. But then he’s also sad that the future will be much older, and less vibrant, than the past.

Anyway, it’s a good article for teaching, but it was written before he even knew the Baby Boom was ending, and before fertility fell all over the world, and so on. If you don’t know that history it can be confusing to read, and if you do know the history it is still distracting and you want to keep looking things up to see what’s going on today.

So I updated it. I just went through and revised as little as I could to make it up to date but still truthful. It was like a game. Took a few hours, but I hope it was worth it. (And I have seven days left before classes start.)

The trickiest part was the discussion of global growth rates over the last 2000 years. He took the world from 250 million people in year 0 to 3 billion people in 1960. I wanted to go to 8 billion in 2024. So this is how I have revised it:

The population of the world has grown from about one-quarter billion to about eight billion since the time of Julius Caesar – it has been multiplied by about thirty-two. (My assumptions here are a population of 250,000,000 in the year 0, and constant birth and death rates through 2024, to arrive at a population of 7.8 billion by 2024.) But the average annual rate of increase has been very little – about 1.7 per 1000 per year. If the world birth rate has averaged 40 per 1000 (a reasonable guess) the world death rate by logical necessity has averaged 38.3 per 1000. A world birth rate only three points lower (37 instead of 40 per 1000) would have led to an annual decrease of 1.3 per 1000, and the current population would be only one-fourteenth instead of thirty-two times the population of Caesar’s day. A birth rate of 35 – that of England or the United States in 1880 – would have reduced the 250 million of two thousand years ago to only three hundred thousand today.

Then the future projections were a little tricky, too. I got it to this:

If, on the other hand, mankind can avoid nuclear war, pandemics, and population decimation because of global climate change, and bring the fruits of modern technology, including prolonged life, to all parts of the world, the human population must become an old one, because only a low birth rate is compatible in the long run with a low death rate, and a low birth rate produces an old population. In fact, if by 2090 the global expectation of life at birth increases to eighty-two – a level achieved by a few dozen countries so far – and the global number of children born per women falls from 2.3 to 1.9, the global population will peak around 10.2 billion. In that scenario, which is the United Nations current projection, the decline in fertility would make the whole world older than the high-income countries today: with 17 per cent under fifteen and 24 per cent over sixty-five (compared with 16 per cent and 19 per cent, respectively, today).

Fun!

If you are a demography student, or teach demography, I hope you’ll consider this for your seminar instead of or in addition to the old one. For your reading or assigning pleasure, I prepared three versions:

• The original (from the 1987 book): https://osf.io/rpc6m
• The edited version, with my changes (just the additions) in red: https://osf.io/5dv68
• The edited version without showing the changes: https://osf.io/yp893

If you are the Ansley estate or own Oxford or Doubleday or whatever, please don’t sue me. I think Coale would have thought this was ok. If you are an authoritarian activist who wants to accuse me of plagiarism to get me kicked out of whatever administrative position I’ve been coerced into taking some time in the future — thank you!