Introduction
The Gaia hypothesis, named after the ancient Greek goddess of Earth, posits that Earth and its biological systems behave as a huge single entity. This entity has closely controlled self-regulatory negative feedback loops that keep the conditions on the planet within boundaries that are favorable to life. Introduced in the early 1970s, the idea was conceived by chemist and inventor James E. Lovelock and biologist Lynn Margulis. This new way of looking at global ecology and evolution differs from the classical picture of ecology as a biological response to a menu of physical conditions. The idea of co-evolution of biology and the physical environment where each influences the other was suggested as early as the mid-1700s, but never as strongly as Gaia, which claims the power of biology to control the nonliving environment. More recently, the terms Gaian science or Gaian theory have become more common than the original Gaia hypothesis because of modifications in response to criticisms and expansion of our scientific understanding.