LONDON - New evidence suggests Africa’s birth rates are falling fast, according to the Economist.

stories of big families inform much of how the world thinks about sub-Saharan Africa, not just now but over coming decades.

At conferences and in cabinet meetings across the continent, politicians and policymakers fret about how to educate, employ, house and feed a population that the un expects to grow at breakneck speed from around 1.2 billion people now, to 3.4 billion people by 2100.

In southern Europe, populists stoke up fears that hundreds of millions of Africans may try to cross the Mediterranean to escape poverty, war or hunger.

Across the rich world, environmentalists fear the impact on the climate and planet of an extra 2bn people.

Yet few have noticed a wealth of new data that suggest that Africa’s birth rate is falling far more quickly than expected.

Though plenty of growth is still baked in, this could have a huge impact on Africa’s total population by 2100. It could also provide a big boost to the continent’s economic development.

“We have been underestimating what is happening in terms of fertility change in Africa,” says Jose Rimon II of Johns Hopkins University. “Africa will probably undergo the same kind of rapid changes as east Asia did.”

The un’s population projections are widely seen as the most authoritative. Its latest report, published last year, contained considerably lower estimates for sub-Saharan Africa than those of a decade ago.

Yet even the un’s latest projections may not be keeping pace with the rapid decline in fertility rates (the average number of children that women are expected to have) that some striking recent studies show.