HOW unusual is Africa’s demography? If you take a selection of countries, from Algeria and Tunisia in the north to 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, meaning the average woman there could expect to have that number of children during her lifetime. That was about the same as fertility in Brazil, China, Indonesia and Mexico at the time. Now, all the countries have similar fertility rates of 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 their fertility stay high until the mid-1980s, then fall sharply.

But a recent study by two French-speaking demographers, Jean-Pierre Guengant and John May*, casts doubt on this picture of convergence between Africa and the rest. The north and south of the continent, they say, 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 though its labour force will also expand (which is potentially good for growth), its coming “youth bulge” will be hard 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 UN had expected in 2010, when it produced its regular worldwide population survey. Since then, 17 African countries with half the continent’s population have reported fertility rates higher than the UN had estimated. Only ten, with 14% of the population, came in lower. In almost all countries fertility is falling. But in about half of them, the fall has slowed down and in a few cases it has stopped.

Using recent figures, Messrs Guengant and May divide Africa into four groups (see map). The first are those which really are converging, with fertility rates below 4.0. There are 13 of them, and they have 22% of the continent’s population. All are either in the north or south, or are islands, such as the Seychelles. Not a single one is in west, central or east Africa.

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 are only starting to converge. This is a group whose members have seen striking falls in fertility for a few years, which have then stalled. 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%.

The next group is almost as large as the first two combined. Its 16 countries include Africa’s giant, Nigeria, which has 170m people, and they account for 37% of the population. They are not really converging—their fertility rates are between 5.0 and 6.0—though their demographic patterns are starting to change, fitfully.

And the last group is seeing even less change. Its members have fertility rates over six, not so different from the 1960s. Most are landlocked; most have low rates of urbanisation. They include Uganda, the Democratic Republic of Congo and Niger, which, at 7.5, has the highest fertility rate in the world.

Add the last three groups together and you find that 78% of Africa’s people live in countries where the transition to low fertility and low mortality (characteristic of the rest of the world) is nowhere near finished. Hence the conclusion that most of Africa is not catching up with the rest.

From a tenth to a quarter

That has big implications for the overall size of the continent’s population. There were 1 billion Africans in 2010. The UN, using its “medium projections” (which imply continued convergence), reckons that the population will increase to 1.6 billion by 2030 and will double by 2050. But if the past few years are any guide, these medium projections are too low. According to the UN’s “high variant” (which implies a slower fall in fertility), Africa’s population will rise to 2.7 billion by 2050. If that were to happen, Africans would then account for more than a quarter of the world. In 1970, they made up only a tenth.

Such an increase in population would be associated with enormous rises in urbanisation and in the number of children. In 2010 Africa had three cities with over 5m inhabitants (Cairo; Kinshasa, Congo’s capital; and Lagos, Nigeria’s commercial capital). By 2050, it could have 35, with Kinshasa and Lagos each exceeding 30m. Other burgeoning mega-cities are Tanzania’s Dar es Salaam, Kenya’s Nairobi and Angola’s Luanda (see chart). Providing basic services to them all will be a nightmare.

There were 411m African children in 2010, aged 14 years or below. By 2050 there will be 839m, according to the UN’s high variant. Educating all those young minds will be expensive. It is true that there will also be lots of new arrivals into the labour force, who should be able to earn the money to pay for their younger siblings to go to school. In 2010 there were roughly 200m Africans between 15 and 24 years of age and this number could rise to over 450m by 2050. But the African Development Bank pointed out in 2012 that only a quarter of young African men and just 10% of young African women manage to get jobs in the formal economy before they reach the age of 30. The vast majority of young Africans will continue to have precarious employment—a worrying prospect.

To make matters worse, many economists fret that the recent story of “rising Africa”—a virtuous circle of economic growth and improved governance—is already starting to wear thin. Dani Rodrik of Princeton University, for example, reckons that manufacturing and private investment have hardly budged despite a decade of rising incomes. Some economists, to be sure, say that Africa is ripe for a manufacturing surge. But it is still the case that African growth depends heavily on commodity exports to China, where demand for raw materials is slowing.

In these circumstances, the demographers argue, African governments need to make a bigger effort to spread family planning. Over 60% of women of child-bearing age use modern contraceptive methods in South Korea, Mexico and Bangladesh. In most of sub-Saharan Africa, the rate is below 20%. Until recently, some governments, such as Uganda’s, even discouraged family planning, though that is changing on the whole. The bigger problem is that social attitudes are not changing much—so, Messrs Guengant and May argue, governments have to do more.

Family planning is not expensive. According to the Guttmacher Institute, an American think-tank, it would cost about $1.5 billion a year to provide modern contraceptives to all African women aged 15-49 who do not get them. 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 will see its demographic convergence lag behind; it also risks getting stuck, by having too many people with too few chances of escaping poverty.

*“African Demography”, by Jean-Pierre Guengant and John May. Global Journal of Emerging Market Economies.