We learn that there are three types of country - ones where we're over the hump and strongly headed for a shrinking, top-heavy, ageing population, ones that are in transition, and ones that at the moment are still in the 'natural' condition of 'have lots of children to survive' leading to population growth as health care gets better and very bottom heavy age distributions.
Throughout, I struggled to understand where Sarah Harper was going with this. When talking about the advanced economies there was clearly a problem of having enough young workers to support the ageing population. But equally, there seemed to be emphasis on moving away from the more traditional population distributions because these had lower average ages and less social benefits - there was no real feel for what the ideal is in population terms, or how to achieve it.
There were also some strange gaps. In talking about how a population got into its current state, there was very little mention of cultural/religious influence on, say, contraception or women's education. This was despite the impact of women's education on birth control getting a large mention - but we get little feel for what restricts this. And the reader is presented with a lot of correlation as if this were clearly causality, but with very little mention of how the causal links are being established.
The book gets most interesting, I think, towards the end, where the contributions of climate change and migration were discussed. But I still got the feel for having vast quantities of data thrown at me with very little attempt to answer the crucial 'And so?' questions. We got a good feel for how population age distributions are likely to change with time (although there is a big dose of uncertainty rather quietly thrown in part way through, without really dealing with it), but no real idea of what the implications are. I can see this book working for students to use as a source from which to write essays - but not as a vehicle for to inform the public on the implications for all of us of the way that the world population is changing.
Review by Brian Clegg