Like them or loathe them, birthdays come once a year, regular as clockwork.

Another candle on the cake heralds us into a new period of our lives: from sweet 16, to the quarter-life crisis at 25, followed by the mid-life crisis at 45 and beyond. We face each birthday like an advancing wave, which we must inevitably embrace.

When that milestone is triple figures, you can't help but stop, stand and think about the huge landmarks of history that punctuate a century of life. My grandmother will no doubt be doing just that when she hits the big 100 this 28 November.

Have I broken the universal rule of etiquette by mentioning a lady's age? Yes, but a centennial celebration is above the fear of faux pas.

In 10 decades, my gran has lived through colossal events in human history; she was in nappies when the Titanic sank, a child during World War I, a young woman during the Wall Street Crash and a wife and mother throughout World War II.

Our family have been making arrangements for the celebration of this impressive life span: invitations sent to children, grandchildren, cousins, uncles, aunts, the local vicar and the obligatory request for a telegram from the Queen.

In the midst of these preparations, a world event put my gran's age in staggering perspective.

On 31 October, All-Hallows-Eve, a day when some cultures around the world mark the date with costumes of ghoulish ghosts, the world's media had another 'celebration' to shout about, one of life, instead of death; the arrival of the seven billionth person.

Out of the 200,000 babies born on that day, one holds the seven-billion crown - it was a lottery in which we will never know the winner. When my gran was born, the world population was 1.7 billion. In a century, the human race has quadrupled in size.

Over the past fortnight, more than ever the age-old debate about the consequences of our rocketing population has been circulating on the Internet and on the airwaves. With the apparent sudden realisation that the population is booming formidably, it feels as though yet another issue has been added to the list of the 21st century's problems; a fresh pang of global guilt for the upcoming 2012.

On our 'fix-it' agenda, we now not only have global warming, the depletion of fossil fuels and the sluggish switch to renewable energy, but population has reared its head as an undeniable fact; the number of people in the world could double in my lifetime.

This perception exhausts many of us with a 'we're all doomed' mode of thinking, but it seems clear that for decades it is the issue of population itself that has been sitting at the top of the tree as the cause of environmental issues facing us.

From as far back as the Industrial Revolution, it is the huge energy consumption of an increasing number of people that has mined away at fossil fuels and created the global warming crisis we struggle with. An obvious fact, I know...but one that appears to be overlooked - it has, I believe, always been about population.

Many organisations champion the possible solutions of an overwhelming population; the United Nations Population Fund say that our priority should be to educate and empower girls and women to allow them to have fewer children than their mothers and grandmothers did.

Contraception could be the answer, but challenges lie ahead, as an aid worker in Africa speaking to the BBC's World Service noted, "Coca-Cola is ubiquitous on the continent, but condoms are rarely seen."

On the opposing side of the debate, organisations like the Population Research Institute believe that population increase is not a problem and should instead be celebrated as an achievement for mankind.

As we hurtle towards eight billion people in the world by 2025, as predicted by the UN, I hope the debate will continue to throng and remain ever present in the public arena.

Despite fears over the population and the earth's resources, there is plenty to celebrate about a world that has produced its seven billionth person in the face of the threat of nuclear warfare.

But is that enough to be satisfied with? Should we strive for an even better world with a manageable population?

I only hope that the leaps in standards of living and advances in medicine that allow the world's privileged few to live long healthy lives, just like my gran, can be brought to all seven billion in the world.

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