Population, part 2: What factors affect the size of the world population?

Yes, let’s look at my next question regarding world population, as stated above.

The answer seems to be really easy, it’s basically the birth rate and  the death rate, which decide whether the world population will increase or decrease. How many babies are born and how many people die?

The birth rate can be affected by things like access to contraception, education, but also cultural differences can affect how many children you want to have.

On the other hand, the death rate can be affected by the access to clean water, food, sanitation, technology, health care and education. Diseases and natural catastrophes can of course strike and cause deaths.

It is said that every woman need  on average needs to bear about 2,1 children to replace herself and her partner. (It is more than 2 children, because of child mortality. This is being calculated based on a child mortality rate in the Western World.)

I also read this interesting article on Wikipedia about the demographic transition, which is a theory on how both the birth and death rates go from high to low as a country develops from a pre-industrial to an industrialized economic system. The Wikipedia article is partly based on a publication by Keith Montgomery from year 2000, published on the web site of University of Wisconsin – Marathon County, which I also read (links below). (Picture below thanks to SuzanneKn [Public domain], via Wikimedia Commons.)

Dtm_pyramids, largerThe theory goes that at first both birth and death rates are high, which keeps the size of the population balanced. Then as the country develops the number of deaths decline due to improvements in the areas listed above, which causes the population to grow, since birth rates still are high. The population consists of more young people than old people, a classic population pyramid.

Then the birth rate starts to go down. It seems like the reasons for this is unclear, but speculations in the articles are that in a more industrialized society, you realize that you don’t need as many children as before to sustain your personal economy and retirement, since the children you bear actually survive. Also values change, women get education and start to work outside the home. The cost of caring for each child gets higher, since the children are not expected to work until they are adults. Women who get education tend to be older when they start to have children. I think women and their partners feel that a lower number of children is ”enough” and the access to contraceptives makes it possible to control how many children to have. When the birth rate goes down, once again the population growth is balanced, but since you had a growth earlier these people get older and older. The population pyramid becomes more of a square.

If the birth rates decline even more, the population pyramid can start to resemble a circle.

But it also seems that it is very hard to predict the future. A BBC article quotes Professor Jane Falkingham: “”We’ve actually got population projections wrong consistently over the last 50 years,” says Professor Falkingham, “and this is partly because we’ve underestimated the improvements in mortality, particularly older age mortality, but also we’ve not been very good at spotting the trends in fertility.“” Another quote from the article:  “”Historically, fertility has been falling across Europe,” says Professor Jane Falkingham, director of the ESRC Centre for Population Change at Southampton University. “But actually if we look at the most recent period, the last 10 years or so, we see rises in fertility in the most advanced countries.””

As I’ve written before the forecasts are that the world population will grow in the near future and Falkingham’s statements seem to indicate that also, but who knows what the future really brings…

Links:
http://en.wikipedia.org/wiki/Demographic_transition
http://www.marathon.uwc.edu/geography/demotrans/demtran.htm
http://www.bbc.co.uk/news/technology-19923200

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