The Gaia hypothesis, put forth by James Lovelock in 1972, proposes that planet Earth is regulated by and for the life forms occurring on the planet. The hypothesis suggests that life has somehow conspired in the regulation of the global environment so as to keep conditions comfortable. In some forms, the Gaia hypothesis suggests that the planet has a “consciousness.”
According to the author, Toby Tyrrell, a professor of Earth system science at the University of Southampton, England, the Gaia hypothesis makes three main assertions:
1. The environment is very well-suited to the organisms that inhabit it. As Tyrrell points out, this assertion is backwards, organisms adapt to the environment; the environment does not adapt to organisms.
2. The Earth’s atmosphere is a biological construct whose composition is far from expectations of (abiotic) chemical equilibrium.
3. The Earth has been a stable environment over time, despite variable external forcings.
Tyrrell also notes two competing hypotheses:
1. The Geologic hypothesis which holds that Earth’s environment is due mainly to geological forces and astronomical processes.
2. The Coevolutionary hypothesis which holds that “life and environment have both changed over time, and that changes in either have had effects on the other.” The difference between this hypothesis and Gaia is that coevolution “is free of any connotations that, once life had evolved and started to influence climate, the planet was bound to remain habitable thereafter.”
Tyrrell has taken on a big job in a critical examination of the three Gaia assertions and the two alternate hypotheses. The book is a tour de force that presents physical and philosophical evidence for and against the Gaia hypothesis, which, Tyrrell points out, has some similarities with Intelligent Design. Fortunately, the book is written in plain language and each of the 10 chapters has introductory paragraphs dealing with what the chapter will cover and a concluding section providing a summary. Many of the endnotes referenced within the chapters are interesting stories in themselves and provide amplifying evidence for the main points.
The book includes over 50 pages of end notes, suggested reading for each chapter, and 22 pages of references to the scientific literature.
Tyrrell ultimately concludes that “Gaia is a fascinating but a flawed hypothesis. It is not a correct characterization of planetary maintenance and life’s role therein. Some of Lovelock’s claims…are seen to be dubious when probed more deeply. Some of the key lines of argument advanced in support of Gaia are insecure, or else give support in equal measure to other hypotheses as well as to Gaia. There is nothing that can be explained only by Gaia.” The evidence shows that the Gaia hypothesis fails on assertions 1 and 3.
Tyrrell favors the coevolution hypothesis which, he says, “is fully compatible with what we know.” “There are no natural phenomena that either Gaia or the geological hypothesis is uniquely able to explain.” While I’m sad to see that geology can’t explain absolutely everything (I’m a geologist), I must agree with Tyrrell.
How he gets to his conclusions is a fascinating story illustrated by many interesting examples. The book is well-written and easy to read. Some of his perceptions may give you a different perspective on things. I particularly like a sentence in Chapter Two: “Nature is a mixture of apparent cruelty and kindness, of economy and waste, of competition and cooperation.” (That’s so Dickensian: It was the best of times….) It sets the tone of Tyrrell’s critical analysis. Tyrrell’s story is very informative and the reader will learn many fascinating things along the way.
P.S. In an interview with MSNBC, on March 17, 2009, James Lovelock admitted that he had been a climate alarmist and had been “extrapolating too far.”