How unusual is Africa's demography?

If you refer to Algeria and Tunisia in the north and Botswana and South Africa in the south, you may answer: not that unusual. In the early 1960s those nations had fertility rates of between 5.5 and 7.5, about the same as rates in Brazil, China, Indonesia and Mexico at the time. Now, all of those countries' fertility rates are between 1.5 and 3.0. The main difference is that the Asian and Latin American nations saw their fertility decline at a fairly steady pace over the past 50 years, whereas the African ones saw a sharp decline beginning in the mid-1980s.

In a recent study, demographers Jean-Pierre Guengant and John May say the north and south of the continent are exceptions. Most of Africa is catching up too little, too late. The result is that the continent's overall population will rise sharply, its big cities will grow alarmingly, and while its labor force will also expand, its coming "youth bulge" will be difficult to manage. They conclude that governments must do much more to encourage and improve family planning.

Recent census and survey data suggest that African fertility is falling more slowly than the U.N. had expected in 2010, when it produced its regular worldwide population survey. Using recent figures, Guengant and May divide Africa into four groups. The first are those with fertility rates below 4.0. There are 13 of them, and they have 22 percent of the continent's population. All are either in the north or south, or are islands, such as the Seychelles.

Africa has 40 other countries, not including South Sudan, which has not yet had its own census. Fifteen have fertility rates between 4.0 and 5.0. They include some of the continent's recent relative economic successes, such as Ghana, Rwanda and Ethiopia, but also a few abject failures, such as Zimbabwe and the Central African Republic. They have the same share of the continent's population as the first group, 22 percent.

The next group is almost as large as the first two combined. Its 16 countries include Nigeria, which has 170 million people. Their fertility rates are between 5.0 and 6.0 — though their demographic patterns are starting to change, fitfully.

And the last group's members have fertility rates over 6.0, not so different from the 1960s. Most are landlocked; most have low rates of urbanization. They include Uganda, the Democratic Republic of Congo and Niger, which, at 7.5, has the world's highest fertility rate.

Add the last three groups together and you find that 78 percent of Africa's people live in countries where the transition to low fertility and low mortality is nowhere near finished.

That has big implications for the overall size of the continent's population. There were 1 billion Africans in 2010. The U.N. reckons that the population will increase to 1.6 billion by 2030 and will double by 2050. But if there is a slower fall in fertility, Africa's population will rise to 2.7 billion by 2050, accounting for more than a quarter of the world's population. In 1970, they made up only a tenth.

There were 411 million African children in 2010, age 14 years or below. By 2050 there will be 839 million, according to the U.N.'s higher estimate. Educating all those young minds will be expensive. It is true that there will also be lots of new arrivals into the labor force. But the African Development Bank pointed out in 2012 that only a quarter of young African men and just 10 percent of young African women manage to get jobs in the formal economy before they reach the age of 30.

Dani Rodrik of Princeton University reckons that manufacturing and private investment have hardly budged despite a decade of rising incomes. And African growth still depends heavily on commodity exports to China, where demand for raw materials is slowing.

In these circumstances, the demographers argue, African governments need to emphasize family planning. In most of sub-Saharan Africa, the rate of women using modern contraceptive methods is below 20 percent. The countries where they are used most frequently are also the ones catching up fastest with the rest of the world. Unless the other African countries follow suit, the continent risks having too many people with too few chances of escaping poverty.

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