The Zoologist’s Guide to the Galaxy: What Animals on Earth Reveal About Aliens — and Ourselves by Arik KershenbaumThe Zoologist’s Guide to the Galaxy: What Animals on Earth Reveal About Aliens — and Ourselves by Arik KershenbaumThe Zoologist’s Guide to the Galaxy: What Animals on Earth Reveal About Aliens — and Ourselves by Arik Kershenbaum

Usually, when one thinks about “universal laws,” the first disciplines that come to mind are mathematics and physics. Pi, or the law of gravity, for instance. But in The Zoologist’s Guide to the Galaxy: What Animals on Earth Reveal About Aliens — and Ourselves, Arik Kershenbaum makes the case for “universal laws of biology.” And then further argues that said laws, which we can formulate based on our experiences and observations here on Earth, can be extrapolated to consideration of just what sort of alien life we may encounter out there in the vast reaches of the universe. And methodical and logical as Kershenbaum is in making his case, he never loses touch with the sheer wonder at its core, making for an utterly enjoyable and absorbing read.

At the center of Kershenbaum’s case is the idea that “the first and most important law is that complex life evolves by natural selection … not just the only mechanism we know for creating complexity out of simplicity … [but]an inevitable mechanism.” After explaining how natural selection works and why it is not dependent on DNA, RNA, an earthly habitat, or any of the other elements of “life as we know it,” he gives a brief overview of aspects such as convergent evolution, kin selection, and reproduction. Then, still in introductory mode, he delves into the definition of “animal”: how we categorize living things as animals or not, how we respond to them in their different categories, and what it would take for us to place aliens in one category or another. After these more general chapters, he devotes a single chapter each to a specific behavior (his interest is not in what aliens may look like but in how they might act): movement, communication, intelligence, sociality, information, and language. Finally, he also tackles the question of artificial life created by aliens.

Within each chapter, Kershenbaum answers the question of why animals (and thus aliens) perform such “inevitable” behaviors and how natural selection drives those behaviors down various paths, some of which are more likely than others. While he uses earth creatures as the specific examples, having no other choice obviously, he always lays out clearly and thoroughly why the rules governing said behaviors are Earth-agnostic, would apply to any life anywhere, though the form of the behavior might differ. For example, in the section on movement, he explains how the laws of physics, which he points out are assumed to be the same on every planet, constrain the types of movement allowed, then runs through the various types we see on Earth, depending on the setting (a fluid setting like water or air or a setting at the junction of a solid and a fluid (think the ground, like us). In a fascinating aside, he explains just why we don’t see “an animal floating through the air under a sack of gas … feeding on atmospheric plankton … [like] a sky-whale.” But then, just as you’re starting to get depressed at the creature’s non-existence, he details just what sort of setting such a creature could live in and why: “a denser atmosphere on a gas giant like Jupiter, or on a smaller planet where gravity is weaker.”

Dr. Arik Kershenbaum

Dr. Arik Kershenbaum

In the segment on communication, after a general discussion of how it would take place through different “sensory channels [or] modalities” he again offers up a number of examples from the animal kingdom — sound, vision, smell, touch, and even electrical fields. He adds as well that while some animals have a magnetic perception, the fact that they don’t use it for direct communication doesn’t rule it out as an alien modality (the same goes for radio waves, he notes). For each modality, he carefully lays out the advantages and disadvantages and then also, for our imagined aliens, explains how their habitat conditions might lead them to have evolved one or another of the modes. For instance, after describing why electric communication on our planet is “either impractical (on land) or unnecessary (where water is clear enough to use other senses,” he points out that on a planet “where the oceans are completely dark … [such as] Titan and Enceladus” it’s quite possible, perhaps even likely, that electrical communication would evolve as a common mode of communication.

Kershenbaum follows a similar pattern in the other chapters. A general definition and overview, such as of intelligence or cooperation, an evolution-based rationalization for its existence, an absolutely captivating tour through its diverse expressions on Earth (crows that use and make tools, a parrot that can do math, dolphins who coordinate their actions and recognize helpmates years after last contact with them), and a based-in-logic speculation on how and why that same behavior would exist in any aliens we meet.

All of this is laid out before the reader in smooth, always clear, easy-to-follow prose with a consistent sense of the curious personality that lies behind it. Kershenbaum simplifies concepts but doesn’t dumb them down to the point of insipidness. While he notes that “Many academics will be deeply distressed at my cavalier approach,” leaving out the complex math at the core of game theory or kin selection for instance, he’s fine in taking that hit, believing that “even if we omit the mathematical fundamentals of why evolution works the way it does, the conclusions I’ve drawn about the nature of alien life will not be harmed.”

It certainly doesn’t feel as if he’s done any harm to the various topics he covers in his simplifying of them. Honestly, if Kershenbaum told me he was planning on expanding each individual chapter into its own book, I’d happily order them all. I’d also say he does himself a disservice in describing his conclusions as being about the “nature of alien life,” as one of my favorite aspects of this book is just how much it illuminates the nature of life on our planets, animal life, yes, but also our own human lives. Which is why this book, as one famous fictional alien would absolutely say about it, is absolutely and endlessly “fascinating.”

Published in March 2021. From a noted Cambridge zoologist, a wildly fun and scientifically sound exploration of what alien life must be like, using universal laws that govern life on Earth and in space. Scientists are confident that life exists elsewhere in the universe. Yet rather than taking a realistic approach to what aliens might be like, we imagine that life on other planets is the stuff of science fiction. The time has come to abandon our fantasies of space invaders and movie monsters and place our expectations on solid scientific footing. But short of aliens landing in New York City, how do we know what they are like? Using his own expert understanding of life on Earth and Darwin’s theory of evolution — which applies throughout the universe — Cambridge zoologist Dr. Arik Kershenbaum explains what alien life must be like: how these creatures will move, socialize, and communicate. For example, by observing fish whose electrical pulses indicate social status, we can see that other planets might allow for communication by electricity. As there was evolutionary pressure to wriggle along a sea floor, Earthling animals tend to have left/right symmetry; on planets where creatures evolved in midair or in soupy tar, they might be lacking any symmetry at all. Might there be an alien planet with supersonic animals? A moon where creatures have a language composed of smells? Will aliens scream with fear, act honestly, or have technology? The Zoologist’s Guide to the Galaxy answers these questions using the latest science to tell the story of how life really works, on Earth and in space.


  • Bill Capossere

    BILL CAPOSSERE, who's been with us since June 2007, lives in Rochester NY, where he is an English adjunct by day and a writer by night. His essays and stories have appeared in Colorado Review, Rosebud, Alaska Quarterly, and other literary journals, along with a few anthologies, and been recognized in the "Notable Essays" section of Best American Essays. His children's work has appeared in several magazines, while his plays have been given stage readings at GEVA Theatre and Bristol Valley Playhouse. When he's not writing, reading, reviewing, or teaching, he can usually be found with his wife and son on the frisbee golf course or the ultimate frisbee field.

    View all posts