You look at the numbers and you think : "That?s impossible." Uganda had about seven million people at independence in 1962, and in only 45 years it has grown to 30 million. By 2050, just over four more decades, there will be 130 million Ugandans, and it will be the twelfth biggest country in the world, with more people than Russia or Japan. Its population will have increased eighteen-fold in less than ninety years.

Many people think that population growth is no longer a problem, and everybody somehow knows that it is politically incorrect to talk about it. Back in 1968, when Paul Ehrlich terrified everybody with his book "The Population Bomb", it was seen as the gravest long-term threat facing the human race, but now it scarcely gets a mention even in discussions on climate change ? as if the number of people producing and consuming on this planet had no relevance to how great the pressure on the environment is.

True, the population explosion has gone away in large parts of the world, in the sense that most developed countries now have birth-rates well below replacement level, and that the global average, including the developing countries of Asia and South America, is now down to 2.3 children. That?s pretty impressive, given that it was 5.4 children per woman as recently as 1970. But there remains the problem of what you might call "inertial growth". My own mother had five children, which was not seen as at all unusual at the time. (There was one year when Newfoundland, my birthplace, beat Guatemala for the honour of havig the highest birth-rate in the Americas.) The next generation of our family, by contrast, dropped to 2.0 : we five brothers and sisters and our five spouses have had a total of just ten children. But that doesn?t mean that our population boom stopped.

If we had just spawned and died, it would have, but we insisted in living on after our children were born. In fact, we?re all still here, although the first grandchildren are already starting to appear ? so where there were once ten of us, there are now twenty-three. It takes two full generations at replacement level before the population finally stabilises.

That accounts for about half of the anticipated population growth in the next forty years, which will raise the total number of people on the planet from 6.5 billion to about nine billion. (In other words, we will be adding as many extra people as the total population of the world back in 1950.) But the other half of the growth comes mainly from Africa, already the poorest continent.

This may explain why it became politically incorrect to talk about population growth around 25 years ago. Nine out of the ten countries in the world with the highest birth-rates are African (the other is Afgha-nistan), and it seemed uncomfortably like pointing the finger at the victim. But runaway population growth is a big factor in making so many Africans victims, and it doesn?t help to stay silent about it.

Sometimes the steadily worsening ratio of people to resources just causes deepening poverty, as in the case of Nigeria, whose population by 2050 will reach 300 million. That is the same as the current population of the US, but Nigeria, apart from being virtually without industry, does not have one-tenth of the natural resources of the US. If those 300 million people live at all, they will live very badly.

Often, however, the growing pressure of people on the land leads indirectly to catastrophic wars : Sierra Leone, Liberia, Uganda, Somalia, Congo, Angola and Burundi have all been devastated by chronic, many-sided civil wars, and all seven appear in the top ten birth-rate list. Rwanda, Ethiopia and Mozambique, which have suffered similar ordeals, are just out of the top ten. Africa, which accounted for only eight percent of the world?s population when most of its countries got their independence in the 1960s, will contain almost a quarter of the world?s (much larger) population in 2050.

Uganda?s birth-rate is seven children per woman, little changed from thirty years ago. Uganda?s president, Yoweri Muse-veni, believes that his country is under-populated, and told parliament last July : "I am not one of those worried about the population explosion. It is a great resour-ce." He has done many good things for his country, but this one blind spot could undo them all. And he is far from alone.