And keeping the numbers, therefore, in the long-term stable.

So since

the fertility rate is assumed by the United Nations to

trend towards the replacement rate of around two, the

population growth rate also tends to converge to around zero.

But what you see on this graph is that the least

developed countries ironically, but not unexpectedly,

have the highest population growth rate.

Those are

the places where family planning is not used.

Those are the places where girls drop out of school early.

Those are the places where women face massive discrimination.

They're not in the labor market, and so the opportunity cost of their time is low.

They're supposed to be home having children, according to the

prevailing social norms, or maybe the desires of their husbands.

Maybe not their own desires

in many places, but traditional societies impose, through cultural and

other means, that kind of pressure for large numbers of children.

Well, to see where fertility rates are right now, we can look at

the next graph, which measures the actual fertility rates up to the year 2010.

And then shows the projections of the

United Nations in this medium fertility projection

for different groups of countries out to the year 2100.

What you see is that, as of 2010, the countries at the bottom of this curve,

which are the more developed, or the developed

regions of the world, are already below replacement rate.

If they continue with that fertility rate for another couple of generations,

the population size will begin to decline in the high income world.

The highest fertility rates in the curve at the

very top of this picture are the least developed countries.

Whereas, in 2010, still the total fertility rate is above four.

Each mother, on average, is having two daughters.

That means the population

is tending to double, generation by generation.

because each mother is replacing herself statistically with two daughters, who

will grow up to be two mothers of the next generation.

That's why the population growth remains so high.

And one can see in this graph, is that for the less developed

regions as a whole and for the world on average,

the fertility rates are a bit above replacement, but

not as high as in the least developed countries.

And therefore, on average, the population growth rate is less than it is in the