If you spend even a modest chunk of your day glued to social-media websites, you'll have seen links to a site called "WTF, evolution?"
There, you can scroll through a parade of bizarre creatures, from the goblin shark (which resembles a fierce undersea unicorn) to the geoduck (a burrowing clam that looks like an amputated finger) to the aptly named blobfish. They're peculiar, all right, but they're not as strange as the creatures David Toomey is on the hunt for in Weird Life.
In fact, such creatures aren't even "weird," according to Toomey's (very precise) definition. That's because, as odd as they may seem, they're still our cousins, genetically speaking. The same goes for the creatures inhabiting places where, just a few decades ago, we wouldn't have imagined that life could take hold at all – places like the hydrothermal vents on the ocean floor, or the interior of the Antarctic ice cap.
All of these organisms, no matter how exotic, are thought to have descended from a common ancestor – a particular arrangement of chemicals that eventually managed to self-replicate – about 3.5 billion to four billion years ago. The key molecule is DNA, which encodes the genetic instructions for each organism. But other chemicals could also, in theory, self-replicate, and non-DNA-based organisms, if they exist, would be one example of weird life. Alternatively, an organism could build proteins out of a different set of amino acids, or make use of a different "solvent" (terrestrial life uses water, but, as Toomey explains, we can imagine organisms that might use ammonia or liquid methane instead).
An intriguing variation would be life in which chemical components are mirror-reversed: In every living organism that we know of, the amino acids have a left-handed geometry, and the sugars have a right-handed geometry. There is nothing to rule out life in which key constituents have the opposite handedness (the scientific term is "chirality"). As Toomey points out, such creatures could be living right here on Earth, forming a "shadow biosphere" alongside our own. (Here Toomey, a University of Massachusetts English professor and writing teacher, cites the work of scientist and author Paul Davies, who has worked extensively in this field, and whose own recent book, The Eerie Silence, covered much of the same ground.)
The bulk of Weird Life is focused on the prospects of life beyond Earth. Within our own solar system, the rocky moons of the giant outer planets hold the most promise. Europa, one of Jupiter's moons, is a prime candidate: Beneath its frozen surface, there may be liquid water, warmed, perhaps, by hydrothermal vents. An equally beguiling world is Titan, the largest moon of Saturn, the surface of which is peppered with lakes of liquid methane, some as large as Lake Ontario. Could there be creatures lurking within Titan's lakes, using methane to facilitate complex chemical reactions, the way terrestrial life exploits water?
And what about the vast universe beyond our solar system? Toomey summarizes the half-century quest that goes by the acronym SETI, the Search for Extraterrestrial Intelligence. Again, readers who have kept up with Davies's work will find much of this to be familiar ground; still, Toomey's account is engaging and provocative. It's also more up-to-date, with references to the recent controversy over arsenic-based life supposedly found in a California lake, as well as results from the Kepler space telescope, which has identified dozens of possibly Earth-like planets beyond our solar system.
As thorough as Weird Life is, it still left me wondering about some basic (perhaps simple-minded) questions. For example, what would happen if you grilled up a steak made from a cow-like creature that happened to be made from opposite-handed amino acids and sugars? Would it smell and taste different from a regular steak? Would it be toxic, or simply undigestable?
The questions raised by the possibility of weird life are certainly stimulating, but I was also struck by some of the numbers concerning "normal" life, mentioned early in the book. As the author notes, biologists have identified only a tiny fraction of the organisms living here on Earth, with as many as 100 million species estimated to be awaiting discovery. These creatures wouldn't be weird, by Toomey's definition, but they may still be worth finding.
Dan Falk is working on a book on the connections between science, art and literature during the Renaissance, to be published next spring.