We humans have always wondered if we are alone, a preoccupation mirrored in our myths, from the Enuma Elish to Star Trek. The discovery of extraterrestrial life would be an earthshaking discovery, even more so than the Copernican revolution which shifted Earth from the center of the universe to its periphery. Scientists have long debated the parameters for such life, and the search has crystallized into the discipline of astrobiology.
Astrobiology theories fall between two positions. One is the mediocrity principle, which posits that we are not in any way special, and given the enormous numbers of galaxies, stars, etc, life -- including intelligent variants -- exists on many other planets. The other is the anthropic principle, which holds that the universe is optimal for human existence and hence we are the sole intelligent life form. The problem with both positions is that they base their statistics on a single sample. Additionally, the anthropic principle totally ignores the element of chance, which played a crucial role at all stages of biogenesis.
Two recent books by Springer-Verlag Publishers have joined the debate: Here Be Dragons by astronomer David Koerner and neuroscientist Simon LeVay; and Rare Earth by paleontologist Peter Ward and astronomer Donald Brownlee. The former has no ideological position, and its authors interviewed practically every scientist who contributed to astrobiology; the latter, by its title alone and by its introductory statement, unequivocally places itself into the anthropic principle camp.
Both books give overviews of the astrophysical, geological, chemical and biological events which resulted in the appearance, perseverance and evolution of life on Earth, with emphasis on the recent discoveries of extrasolar planets and extremophilic bacteria. Rare Earth is organized in the traditional trajectory of such books, tracing the terms of the much-(ab)used Drake equation. Here Be Dragons is organized less linearly and includes a chapter on UFOlogy. Both books range widely across disciplines and require considerable prior knowledge to read easily and evaluate critically; their style is even but colorless, and their rare flights of literary fancy barely achieve liftoff (for example, the toy sailboat/bacteria and ocean liner/eukarya analogy in Rare Earth).
In Here Be Dragons the style is dictated by the fact that the book is a collection of opinions, which show the fragmentary nature of the data, as well as the deep divisions of scientific opinion over the question of extraterrestrial life. In Rare Earth, the authors present the theories they favor as complete and widely accepted, masking the fact that many are controversial (for example, whether star metallicity is as rare as they describe and whether Cambrian Ediacarans represent additional extinct phyla). Furthermore, I spotted errors in my field of expertise (conflation of transcription and translation, a 20-fold exaggeration of the number of human genes -- both pertaining to the crucial concept of complexity) and a howler regarding the rotations of Mars and Venus (which are not locked, as the authors assert in their haste to make Earth unique in the solar system), These missteps make me wonder whether the authors misquoted additional facts instrumental to their hypothesis.
Which brings us to the crux of the matter, the hypothesis. The rare earth theory is that though bacterial life may be common in the universe, intelligent life -- in the form of terrestrial animals and plants -- is unique. The prediction: upon examining other planets, we'll find that bacterial life is common, and intelligence absent -- a circular argument as, indeed, are all variants of the anthropic principle. In science, theories cannot be identical to their predictions, nor can their predictions be trivial. In fact, the rare earth theory is neither hypothesis nor prediction, but a description of how life arose on Earth.
Calculating probabilities after the fact is equivalent to placing a bet after the race has been run. Conversations about the rarity of intelligent extraterrestrial life rest upon an enormous assumption which Ward and Brownlee, to their credit, mention once per chapter -- that life elsewhere will be life as we know it. Their oft-repeated statement that both Earth and humans are unique is neither novel nor contested -- nor helpful in predicting life elsewhere. Given our current almost total lack of knowledge, such books serve as reviews of existing evidence and as mirrors of the philosophical preferences of their authors; as such, they quickly become obsolete. Theorizing will never substitute for observation and experimentation. As for life elsewhere, Hamlet said it best -- and our universe, with its quirkiness, backs him up:
There are more things in Heaven and earth, Horatio,
Than are dreamt of in your philosophy.
About the Reviewer: Athena Andreadis came to the US at the age of 18 and graduated magna cum laude from Harvard. She holds a PhD in Molecular Biology from MIT, is Assistant Professor of Neurology at Harvard Medical School and the author of To Seek Out New Life: The Biology of Star Trek. Her essays, book reviews and fiction can be seen at www.toseekoutnewlife.com
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this page last updated 28 December 2002
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