As the world population reaches seven billion people, the BBC's Mike Gallagher asks whether efforts to control population have been, as some critics claim, a form of authoritarian control over the world's poorest citizens. The temperature is some 30C. The humidity stifling, the noise unbearable. In a yard between two enormous tea-drying sheds, a number of dark-skinned women patiently sit, each accompanied by an unwieldy looking cloth sack. They are clad in colourful saris, but look tired and shabby. This is hardly surprising - they have spent most of the day in nearby plantation fields, picking tea that will net them around two cents a kilo - barely enough to feed their large families. Vivek Baid thinks he knows how to help them. He runs the Mission for Population Control, a project in eastern India which aims to bring down high birth rates by encouraging local women to get sterilised after their second child. As the world reaches an estimated seven billion people, people like Vivek say efforts to bring down the world's population must continue if life on Earth is to be sustainable, and if poverty and even mass starvation are to be avoided. There is no doubting their good intentions. Vivek, for instance, has spent his own money on the project, and is passionate about creating a brighter future for India. But critics allege that campaigners like Vivek - a successful and wealthy male businessman - have tended to live very different lives from those they seek to help, who are mainly poor women. These critics argue that rich people have imposed population control on the poor for decades. And, they say, such coercive attempts to control the world's population often backfired and were sometimes harmful. Population scare Most historians of modern population control trace its roots back to the Reverend Thomas Malthus, an English clergyman born in the 18th Century who believed that humans would always reproduce faster than Earth's capacity to feed them. Giving succour to the resulting desperate masses would only imperil everyone else, he said. So the brutal reality was that it was better to let them starve. Rapid agricultural advances in the 19th Century proved his main premise wrong, because food production generally more than kept pace with the growing population. But the idea that the rich are threatened by the desperately poor has cast a long shadow into the 20th Century. From the 1960s, the World Bank, the UN and a host of independent American philanthropic foundations, such as the Ford and Rockefeller foundations, began to focus on what they saw as the problem of burgeoning Third World numbers. The believed that overpopulation was the primary cause of environmental degradation, economic underdevelopment and political instability. Massive populations in the Third World were seen as presenting a threat to Western capitalism and access to resources, says Professor Betsy Hartmann of Hampshire College, Massachusetts, in the US.
As the Grand Canyon formed, it became a physical barrier to the mixing of squirrels from its northern and southern sides. Each squirrel population was confined to a single side. This type of separation is referred to as geographic isolation.
Plant cells have a large central vacuole because a plant cells requires much more water to function. Vacuoles in animal cells can store water, but they mainly store waste or nutrients
