Over six billion people live in the world today. This is nearly FIVE billion more than a hundred years ago. And even though there has been an explosion in the world's population, the size of the earth remains the same.
The capacity of the planet to feed everyone was a concern two hundred years ago...but the developement of technology has proved that we can now produce enough food to feed us all, even though this is not well distributed.
Now, at the beginning of the 21st century and fifty years after the introduction of the contraceptive pill, the worries are some countries have too many babies while others have too few. The Big Question: Are we too many people for the world?
In 1798, the British political economist Thomas Malthus wrote An Essay on the Principles of Population
Malthus' basic theory was that the world's population was not going to be able to feed itself unless the population growth was controlled. Through the years and with the development of technology, Malthus' theory proved to be wrong, but even so his essay has become the foundation of population studies and demography as we know it today.
Malthus' essay was published just before the "industrial revolution" and his theory appeared to be no longer relevant within an industrial society. With the exploitation of fossil fuel, the introduction of machinery and later the wide spread use of fertilizers it is possible to produce more food from the same patch of land.
Alongside a massive growth in world population, global fertility and mortality rates have dropped in the last century. Fertility rates have fallen mainly due to the introduction of contraceptive methods, while the decline in mortality rates can be explained by the improvement of medicine and health services in general.
The introduction of new contraception methods have shaped the world population for much of the last fifty years. "The pill separated 'sex for love or fun' from reproduction, - people wanted to have sex [for reasons other than] reproduction", says Dr Carl Djerassi. A professor of chemistry at Stanford University, Dr Djerassi is the "father of the birth-control" pill: he synthesized the first oral contraceptive in 1951. Crucially, the Pill gave the women the power of control over when they wish to become pregnant.
With the introduction of contraception the fertility levels in certain European countries and in Japan are so modest that each successive generation will only be two thirds the size of its predecessor. Demonstrating this, some Italian villages struggle to maintain a population, while Japan has to reform pensions to cope with population change.
However, while demographers say the fertility levels are lowering around the world, this is not yet the case in places like the Middle East, certain African and Asian countries and Latin America.
Dr Djerassi says: "When I was born in 1923, there were 1.9 billion people in this world. Now there are 5.8 billion. At my 100th birthday, there will be 8.5 billion. That has never happened in human history before and will never happen again, that during a person's lifetime, the world population has quadrupled."
China is the most populated country in the world. The 1.3 billion Chinese represent one fifth of the world's population. Due to population growth in the past, the Chinese government introduced in 1979 what is called the One Child Policy to slow down the population growth.
Emma spoke to Professor Xizhe Peng, Director of the Institute of Population Research, Fudan University in Shangai and editor of the book The Changing Population in China who explained how this policy was implemented - and what new problems has it created.
A recent report by the US census bureau, projected a decline in the size of Africa's population as HIV AIDS impact on population is felt. But while Africa has the world's highest rate of HIV infection, over the next fifty years Nigeria's population is expected to more than double. For Nigerian author, Buchi Emecheta, author of the book The Joys of Motherhood, it will be women who'll pay the price.
In other places, like Colombia, there are people who believe in the flowing of the energy between themselves and the environment. A tribe called the Taimucas - translated as the ash people - live along the rivers of the Amazon Basin; they believe that they are part of the environment and that it is important to keep the energy flowing.
According to them, the amount of energy that gives life to an environment is limited. The Taimucas believe that illness and death come because there's been an abuse of the energy. Sexual restriction is a part of the rituals they practice to control the population - and to give back the energy to the environment.
This edition of The Big Question was first broadcast on 29th May 2004