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In the niche between science fiction and science exposition lies the too-rarely visited genre of science speculation, where inventive authors explore the outskirts of possibility and stretch readers' minds to the limits of plausibility.
There, SF-fans seeking something more realistic find common ground with skeptical science readers craving something more imaginative. Both will find an intellectual treat in What Does a Martian Look Like? The Science of Extraterrestrial Life by best-selling team of Jack Cohen (a reproductive biologist) and Ian Stewart (a mathematics professor).
Most authors approach life in the Universe from the perspective of astrobiology, a frontier science rooted in knowledge of life as we know it and Earthlike habitable worlds. "Jack&Ian," as the authors are wont to call their mind-meld, contend that the study of extraterrestrial life demands a more radical approach, which they call "xenoscience."
Alien intelligence, they argue, may come in many forms, with terrestrial analogs (such as the patrons in famous Star Wars bar scene) the least likely. Even DNA-based organisms that evolve on planets with conditions similar to our own would most likely have body-plans unlike any we know. What capabilities, like sight, are universal and likely to evolve wherever earthlike conditions, like a steady flux of light, prevail? What features, like mouth below nose, are parochial and the result of a particular evolutionary path that may not be duplicated?
DNA chemistry is not necessarily the only carbon-based path to life, Jack&Ian suggest. If another alternative had taken hold first, an entirely different ecology might have arisen. Likewise, a chemistry of life not founded on carbon might be better adapted to a planet or solar system with a different composition than ours.
And who is to say that life is necessarily chemical and that the abodes of life are necessarily planetary? Reproducing magnetic structures might live in the interior of stars, evolving an ecology, intelligence, and "extelligence" -- Jack&Ian's word for collected and shared knowledge that leads to rapid innovation and communication.
The book would be a total delight except for a misstep that jars readers who previously enjoyed the thought-provoking book Rare Earth by Peter D. Ward and Donald Brownlee. Ward and Brownlee describe the fortunate series of events and planetary characteristics that led to the evolution of intelligent, communicating life on Earth. Such a combination is rare, they argue. Jack&Ian disagree, but go an unnecessary step further. They attack the thesis of Rare Earth as unimaginative rather than acknowledging the authors' natural scientific skepticism.
Contrary to its authors' contention, What Does a Martian Look Like? does not ask readers to be more imaginative than they are; it simply asks them to suspend their skepticism. That's the great pleasure of the book, and is doesn't have to attack another book to prove it.