The Gaia hypothesis affirms that the earth is not just a place where life is found but that is itself a living organism ("Gaia"). It may be compared to the human body where billions of cells interact to make a single living being. The life forms on earth in all their diversity work together as a coherent, self-regulating living system. They interact with chemical, physical, biological, and geological forces and adapt and coevolve over time to maintain a balanced environment and to produce the optimal conditions for the growth and prosperity not of themselves but of the larger whole. Gaia may therefore be defined as a single yet complex living system involving the biosphere, atmosphere, oceans, and terrestrial crust. These interact to keep in balance the surface temperature of the earth and the oxygen levels of the atmosphere, just as our bodies regulate their own temperature and the oxygen levels in their arteries.
The hypothesis was formulated by the British scientist James Lovelock, while he was working for the U.S. NASA space program in the 1960s on experiments to detect the possibility of life on Mars. He realized that the atmosphere of a planet with life was fundamentally different from that of a dead planet like Venus or Mars. The name Gaia (the ancient Greek earth-mother goddess) was suggested to Lovelock by the novelist William Golding because of her dual role as a caring supporter and a ruthless annihilator. The name Gaia perhaps encourages a false tendency to view the earth anthropomorphically, with the equatorial rain forests functioning as the planet's lungs, the rivers and streams as its veins, the mountains as its bones, and living organisms as its senses. But the hypothesis does not imply that the earth actually is a goddess, or indeed any kind of sentient being with awareness, foresight, or intention. It is perhaps more helpful to view the earth as alive in the way a tree is alive-with much dead tissue, yet using sunlight, water, and minerals to grow and change over time.
The Gaia hypothesis has been criticized by scientists such as Richard Dawkins who argue that as Gaia cannot reproduce herself, she cannot be said to be alive in any meaningful way. However, while the hypothesis has by no means been substantiated (and indeed it is difficult to know how it could be), it has generated much scientific research. Lovelock has said himself that the hypothesis may just be a different way of viewing the facts we know about the earth. Some people find it easier to understand as a metaphor rather than a literal scientific statement, reflecting the interdependence of life and affecting the way we view the earth.
As a metaphor, Gaia can be said to encourage cooperation rather than competition and the avoidance of damage through deforestation or carbon dioxide emission. For Lovelock, Gaia is a religious as well as a scientific concept, though often the response to the hypothesis goes beyond his own view of humanity as peripheral, though dangerous, to the life systems of the planet. For many people, the Gaia hypothesis encourages a spiritual dimension in their relationship with the earth, and affirms the sacredness of what they have been conditioned to treat merely as resources to be exploited. Though it is claimed that the Gaia hypothesis does not conflict with any of the major world religions, it strikes a chord particularly with the beliefs of alternative communities and new forms of spiritual thinking in its emphasis on people's inner sense of connection with something larger than themselves. For some, too, it provides the motivation to live on a sustainable basis with other species and the earth's finite resources.