A few hypotheses about population and economic growth – by themselves I don’t think any of them are really disputed although they are rarely put together
1. A wide variety of different levels of population can be sustainable providing the population can be sustained by non-fossil fuel sources of energy and there is sufficient land for growing food that does not require clearance of important biosinks
2. It is changes to population that are most important as a cause (and effect) of economic growth – more so than the absolute level of population
3. The most important factor is the changes that lead to changes of the dependency ratio – (proportio of working to non-working)
4. Very high birth rates are associated with poverty – because of the number of mouths to feed per working adult
5. Falls in high birth rates increase growth – immediately through increasing female participation and reducing dependency ratios – and a secondary pulse in 18 or so years time – this is what we have seen in Ireland
6 But very rapid falls in infant mortality caused by economic growth cause a ‘demographic drag’ effect through increasing the dependency ratio and young people coming onto the labour market more quickly than they can be absorbed – this is what we are seeing in Arab cities
7 Rapid increases in death rates of adults have a strong wealth effect through inheritance of middle and upper classes (as we saw after the black death and wars) that is likely to outweigh the increased dependency ratio – as we are now seeing in Russia with men dying of alcoholism and population falling yet very strong economic growth – the dependency ratio falls if men never reach old age – one of the the causes of the baby boom long economic boom
8. A sharp fall in the birth rate will in the short term boost growth through reducing the dependency ratio but after 18+ years will increase it causing a fierce slow down in growth – this is what we are seeing in China
9. If a society is heavily indented it needs a falling dependency ratio to pay it off – heavy debt and a rising ratio is a recipe for disaster – Japan a decade ago – US now – Germany in 10 years time.
10. If a society has a low level of debt it can afford a rising dependency ratio as it can borrow to make up the difference.
11 If a society/economic system runs out of agricultural land food prices will rise causing immense disruption and instability – there will be an incentive to innovate raising agricultural productivity (the Boserup effect) but the effects will take a number of years – so in the short term regimes have to borrow and import.
12. If the level of debt gets too high and real incomes fall too much relative to rising food prices then you get regime change, land reform and debt cancellation.
13. See 1 above we are running out of agricultural land and in recent years productivity of food/unit of agricultural land has been rising slowly compared to the massive increases in the 70s and 80s.