Last month we saw how there is a parallel universe of worms which have evolved to live within us. Their existence depends entirely on ours. Our bodies create a comfortable environment  maintained by our physiology at a steady temperature, with abundant food and balanced chemical conditions.

Some of  the creatures  living within us are essential for our well being. For example, the bacteria which inhabit our guts are important aids to digestion. Indeed, it is believed that some of the components of cells such as mitochondria (the energy factories) and chloroplasts (which carry out photosynthesis) began as free living bacteria. They became involved in very close relationships with early single-celled organisms and merged together via a process called "endosymbiosis" to evolve into something more than the component parts: a cell with a nucleus.

Our bodies are composed of millions of such cells, which work together in concert and maintain our physiological balance. However, we, and all other multicellular organisms are more than just a collection of cells. The way our cells are organised and interact with each other creates something more than the component parts. This "something more" is called  an "emergent property".

What if we should take this idea and scale it upwards? What if all living things, interacting together, are merely the cells of something bigger, the cells of "something more" comprised of the entire earth?

This is the thinking behind a simple and attractive hypothesis which was born in the mid 1960s.  It started when James Lovelock (independent scientist and inventor) was asked to help NASA develop some tests to determine if there was life on Mars. When he analysed the Martian atmosphere, he saw that it was in a stable chemical equilibrium. This is precisely how you would expect the atmosphere to be, if you created a planet and let it be governed by the basic laws of physics and chemistry. The stable Martian atmosphere is in stark contrast to the atmosphere of Earth, which is in a state of extreme disequilibrium as a result of the metabolic activities of life.

Lovelock asserted that there could be no life on Mars. Ten years later the Viking landings confirmed his conclusion (though scientists are still looking!). His observations made Lovelock wonder how the earth's unlikely atmosphere could be maintained. He concluded that the activities of life must have created a feedback mechanism which maintained the environmental conditions to support it.

He wrote:

"...the physical and chemical condition of the surface of the Earth, of the atmosphere, and of the oceans has been and is actively made fit and comfortable by the presence of life itself. This is in contrast to the conventional wisdom which held that life adapted to the planetary conditions as it and they evolved their separate ways.''

Lovelock's main collaborator in developing this theory is Dr Lynn Margulis. While Lovelock studied planets, Margulis studied microbes and originated the idea of endosymbiosis as the origin of mitochondria. She believes that symbiosis is the driving force behind evolution and that it is the cooperation between organisms and their environment, rather than competition among individuals, the chief agent of natural selection.

Lovelock and Margulis began to believe that the combined totality of life on earth had an "emergent property" and they called it "Gaia" after the Greek Goddess of earth. In 1979 Lovelock wrote:

"The entire range of living matter on Earth from whales to viruses and from oaks to algae could be regarded as constituting a single living entity capable of maintaining the Earth's atmosphere to suit its overall needs and endowed with faculties and powers far beyond those of its constituent parts...[Gaia can be defined] as a complex entity involving the Earth's biosphere, atmosphere, oceans, and soil; the totality constituting a feedback of cybernetic systems which seeks an optimal physical and chemical environment for life on this planet."

He noted the stability of oxygen levels in the atmosphere, the constancy of the earth's surface temperature, which has remained between 10C and 20C over the past 3 billion years, even though the sun's strength has increased more than 30%; how carbon dioxide helps to balance the temperature; and how the saltiness of the oceans has been constant over millions of years, when it should have been increasing.

The idea of Gaia quickly attracted many adherents and evolved into different variants. Some scientists saw it just as a different way of thinking about global ecology. Others, including Lovelock himself, try think of Gaia in strictly mechanical and cybernetic terms, studiously avoiding any hint of hidden purpose or design. However, the way we use language makes this difficult to express. Many, mainly non-scientists, see it as a new view of how humans should relate to the planet and to other living things. Some see Gaia as conscious super being, a goddess or other type of divine presence.

Sometimes Lovelock himself teeters on the edge of mysticism: "To what extent is our collective intelligence also a part of Gaia? Do we as a species constitute a Gaian nervous system and a brain which can consciously anticipate environmental changes?" (Lovelock, 1988, The Ages of Gaia)

Needless to say, there have been numerous criticisms. Many of these stem from the fact that most scientists are "reductionist" in their thinking. That is, when they study something complicated, they break it down into its component parts in order to analyse them, then put the parts back together to try to understand the phenomenon as a whole. 

Holism, or the "top-down" approach, is the exact opposite. It is the studying of a complex phenomenon as a whole, before understanding its components. The Gaia theory is holistic, and so, to a traditional scientist, more akin to a religion than a scientific hypothesis. The use of the name "Gaia" hasn't helped its reputation in the scientific community When the concept is described as "Geophysiology" or investigated under the headings of  "Earth System Science" it becomes more acceptable to scientists.

Unfortunately, the hypothesis of Gaia is untestable. It cannot be proved or disproved. It will remain unproven, unless one day mankind has the opportunity to try to transform a dead planet such as Mars into one which supports life.

One of the major critics of Gaia is Dr. Peter Ward. He asserts that life is actually doing its best to commit suicide, rather than working to maintain the world in a habitable state. He calls this idea the "Medea Theory," after the murderous wife of Jason in "Jason and the Argonauts." Ward notes that there have been many mass extinctions during the history of the world, and ascribes most of these to the activity of living organisms.

Way back, the evolution of photosynthesis created an oxygen atmosphere which killed most of the previous life forms. Later, photosynthesizing plants removed so much carbon dioxide from the atmosphere that the world was plunged into the deep freeze of the snowball earths. (See XAD, August 2009). Dr. Ward ascribes the Permian extinction to microbes which belched out sulphur dioxide, and maintains that the fact that if we are alive today it is just good luck. He predicts that 500 million years from now all plant life will die due to insufficient carbon dioxide, and that eventually earth will become lifeless once more.

Perhaps Dr. Ward is right, and Gaia is so much wishful thinking. Perhaps this emergent property of life is only a short-lived orderly phenomenon in the chaos of the universe. Like a whirlpool in a turbulent stream, it suddenly appears. We can see it and describe it. It seems real, dynamic and stable as it whirls round. And then suddenly it is gone. 

by Christine Betterton Jones - BSc. (Zoology), PhD (Parasitology)

Bibliography:

Gaia's Evil Twin, Peter Ward, New Scientist 20 June 2009.

Gaia Theory, Sebastian Molnar 1999 http://www.geocities.com/we_evolve/Evolution/gaia.html

The Gaia Hypothesis, http://www.kheper.net/topics/Gaia/Gaia_Hypothesis.htm

The Gaia Hypothesis proposed by Dr. James Lovelock in collaboration with Dr. Lynn Margulis - PRF Brown, Mountain Man Graphics http://www.mountainman.com.au/gaia_jim.html
Gaia Hypothesis Wiki http://en.wikipedia.org/wiki/Gaia_hypothesis

Llyn Margulis http://en.wikipedia.org/wiki/Lynn_Margulis