Walk around the American Museum of Natural History and you’ll see some odd biological specimens. Green fuzz, fluorescent blobs, muscular tubes and swarms of bipeds paying good money to stare at rocks. But by the standards of “Weird Life,” by David Toomey, those sights are positively pedestrian.

In his exploration of biodiversity, real and hypothetical, Toomey starts close to home, on Earth. For years scientists have documented extremophiles — microorganisms fond of extremes in temperature, pressure or acidity. (Just a few weeks ago, researchers discovered bacteria in an Antarctic lake under half a mile of ice.) Some bacteria survive in rock, others in clouds. But extremophiles are just Toomey clearing his throat. All the life we know of evolved from the same primordial ancestor; by “weird,” he means organisms with an independent origin and a family tree all their own. His book considers whether and where and how such entities might exist.

Depending on what materials were available at inception, life as we don’t know it might rely on ammonia instead of water, or arsenic (poison to us) instead of phosphorous (possibly poisonous to them). “If life had taken a different course,” Toomey writes, “then we — or weird-life versions of us — might be suffering through summer stock productions of ‘Phosphorus and Old Lace.’ ” Raising the specter of a shadow biosphere here on Earth, he attenuates the ominousness of such a prospect by likening it to “the realm of fairies and elves just beyond the hedgerow.”

Early on, Toomey pauses to clarify exactly what we’re hunting for. A brain trust organized by the National Research Council decided after five years that defining life was futile, but they noted that the best definitions were along the lines of “chemical systems capable of Darwinian evolution.” Biologists generally agree that life requires an energy source, a semipermeable membrane and macromolecules, but this is a list of features, not a fundamental theory. Finding life not like our own, however, might help us discover universal biological laws, similar to physical laws. Knowing how common it is for life to evolve might also rejigger our envisioned place in the cosmos. Those might be reasons enough to search for it.

So off we go, knocking on neighbors’ doors. Several missions to Mars have poked around for evidence of life-supporting conditions. Scientists have also looked to Jupiter’s moon Europa, where microbes could be hanging out near hydrothermal vents in an ocean under its thick icy crust, and to Saturn’s moon Titan, where microbes might breathe hydrogen and bathe in liquid methane, eschewing the Earthling-preferred oxygen and water. And once upon a time Carl Sagan and a co-author proposed, in a scientific article, an ecology in Jupiter’s atmosphere based on thin-skinned, hydrogen-filled “floaters” the size of cities. Farther out, NASA’s Kepler space telescope is finding hundreds of new planets every year, out of the hundreds of billions that might exist in our galaxy.

’Weird Life: The Search for Life That Is Very, Very Different from Our Own’ by David Toomey (W. W. Norton)

Floaters, huh? Toomey’s just getting started. Critical to this book’s ethos is his unrelenting attitude: Sure, that would be weird, but can we get weirder? What about organisms trillions of years from now existing as interstellar clouds of dust that communicate by electromagnetism, or as the interaction of matter surrounding black holes or white dwarf stars? These possibilities have been considered.

Can we get even freakier? Yes. The multiverse. Other universes might have different forces, or discontinuous time, or extra dimensions. In that spirit, do simulated worlds on computers count as universes, with creatures made of bits living within? Which leads to: Are we a simulation? (By one reckoning, we probably are.) Finally, we’ve reached a good stopping point. Yonder be dragons, or not. It’s pure surrealistic speculation, with diminishing scientific returns.

“Weird Life” includes many fields: biology, organic chemistry, planetary science, nuclear physics, astronomy, cosmology. And Toomey, a science writer and English professor at the University of Massachusetts at Amherst, pulls them together with amiable humor and appreciable verbal efficiency. In most cases he provides just the right amount of explanation — though in a few cases I wish he’d gone one step further (why, exactly, does life require macromolecules?). The book also lacks much discussion of how probable its various possibilities are, but presumably hard numbers are hard to come by.

“Weird Life” is a good general introduction to science — and to the scientific process, demonstrating the abundance of disagreement, noting the importance of experimental replication, underscoring the influence of starting assumptions, and even pondering the differences in perspective between disciplines. The astronomers and physicists, who think big and think abstract, tend to be more optimistic and free-ranging in their considerations of weird life in the universe, with the sourpuss biologists pointing out the level of complexity required to make it all happen.

Does weird life exist? Toomey notes that if the universe is indeed infinite, flat and filled with stuff, as is thought, then all possible arrangements of matter, and of life, are out there — and out there an infinite number of times. So yes, weird life exists. Will we ever find it? We can hope to — if we’re clever, and patient, and we don’t first annihilate life as we know it.

Matthew Hutson , a science writer living in New York City, is the author of “The 7 Laws of Magical Thinking: How Irrationality Keeps Us Happy, Healthy, and Sane.”


The Search for Life That Is Very, Very Different From Our Own

By David Toomey

Norton. 268 pp. $25.95