First, parts of Africa are far from empty - Kenya was a land- surplus country 40 years ago, but is now land-scarce. Second, the amount of space, even of cultivable land, is hardly relevant. Agriculture needs investment in infrastructure and research; and productivity today, whether in agriculture, manufacturing or services, needs human investment in health and education.
With populations doubling in 25 years, African governments simply cannot keep up with public services; nor could the private sector, even under improved economic policies, produce adequate employment with rising incomes for such fast-growing numbers. People do not live by space alone.
Equally, there are problems at the individual level. Mothers who bear the average number of children in Africa stand about a one-in-20 chance of dying in childbirth; they will spend about one-third of their lives in pregnancy and lactation, with consequently diminished life opportunities. Children, especially girls, with large numbers of siblings have reduced chances of schooling; if they are born at short birth intervals, as is common when family size is large, they have reduced chances even of living into adulthood.
The message that the industrial countries have been delivering in Cairo has been a subtle one: they have not been saying, as the distorted versions put about by Catholic and other critics have alleged, that family planning will solve Africa's, or anywhere else's, problems. They have been saying that one-quarter of births in the Third World are unwanted by the parents, and that family planning should be extended to those who already want it and cannot get it.
That implies, though, that three-quarters of births are wanted. For most parents, improvements in other aspects of life - child mortality going down, education and employment rising - will be needed before they take to small families.