The billion-mark was reached only after 1800 AD. When Jesus was born, there are thought to have been around 300 million people on earth.

In the days ahead, a baby will be born who will take the global population above 7 billion for the first time, and in all probability that birth will take place in China or India, the two countries with more than a billion inhabitants.

No one is sure. There may already be 7 billion passengers on spaceship earth, as no statistician would be prepared to say exactly when this event of largely symbolic significance takes place.

The United Nations has fixed October 31 as the date of the fateful birth, but events have so often proved demographers wrong in the past that the expectation is that it will be sooner rather than later The rate of population growth has soared over the course of recorded history: When Jesus was born, there are thought to have been around 300 million people on earth.

The billion-mark was reached only after 1800. As many as a billion have been added in the eleven years of the 21st century alone, and predictions on future population growth are now treated with the same caution and scepticism as long-range weather forecasts.

David Bloom of the Harvard School of Public Health says that the multitude of unpredictable factors means that taking a global view is problematic.

“Among them are infectious diseases, war, scientific progress, political change and our capacity for global cooperation,” he says.

The general expectation is, however, that population growth will tail off, with U.N. predictions for 2050 ranging from 8.0 to 10.5 billion.

What is clear is that the proportions will shift between the continents, driven by high birth rates in Asia and Africa. Soon India, with 1.2 billion currently, will take the lead from China, with 1.3 billion, as the world’s most populous nation.

Nigeria, Africa’s most populous country today with 162 million, will see its population increase to almost 750 million by the middle of the century.

Another example: highly industrialised Germany and developing Ethiopia each have a little more than 80 million people. In another 40 years, there will probably be 174 million Ethiopians, while Germany’s population will decline to 72 million.

And the industrialised world is ageing rapidly.

This also means that relations of political power will change.

Countries like China, India and Brazil, with its 193 million people, are already growing in political influence.

This has led European leaders, like German Chancellor Angela Merkel, to warn that “in a world of 7 billion people, we 500 million Europeans will have to stick together,” or European prosperity and values will both go down the drain.

The sheer weight of numbers means increasing pressure on land, food and energy sources, and there are increasing fears of a struggle for resources. Many believe that there will be wars between neighbouring countries over water.

The environmental organisation WWF estimates that three planets will be needed by 2050 if we do not change our habits.

“In the next 40 years we will have to produce the same amount of food as over the last 8,000 years,” the WWF’s Jason Clay believes. He notes that far too much is still thrown away in the industrialised world.

The optimists note that there have been repeated apocalyptic warnings of impending doom resulting from population growth, although they have not yet been realised.

In fact, technical and medical achievements have often led to a more positive outcome than that feared - not only as a result of the Pill and condom, but also through agricultural improvements.

And even the current population mark being passed takes on a new perspective when compared with the number of people the earth has played host to over the course of human history.

It is estimated that since Homo sapiens first appeared, there have been more than 100 billion of our kind - against which the current 7 billion should be set.