nine billion and the UN doesn't ex

It could take 15 years to reach nine billion and the UN doesn't expect to reach 10 billion until 2080.

It's hard to calculate the number of people in the world accurately, and the UN admits its sums could be out by a year or two.

But 15 November is its best estimate for the eight billion line to be crossed.

In previous years, the UN has selected babies to represent the five, six and seven-billionth children - so what can their stories tell us about world population growth?

A few minutes after he was born in July 1987, Matej Gaspar had a flashing camera in his tiny face and a gaggle of besuited politicians surrounding his exhausted mother.

Stuck at the back of a motorcade outside, British UN official Alex Marshall felt partially responsible for the momentary chaos he had brought upon this tiny maternity unit in the suburbs of Zagreb.

"We basically looked at the projections and dreamed up this idea that the world population would pass five billion in 1987," he says. "And the statistical date was 11 July." They decided to christen the world's five-billionth baby.

When he went to the UN's demographers to clear the idea they were outraged.

"They explained to us ignorant people that we didn't know what we were doing. And we really shouldn't be picking out one individual among so many."

But they did it anyway. "It was about putting a face to the numbers," he says. "We found out where the secretary general was going to be that day and it went from there."