In “The Zoologist's Guide to the Galaxy”, Dr Kershenbaum suggests studying life on Earth should lead to an understanding of what extraterrestrial life could be like. He explores the biological laws and rules governing life, examining what life is, why it exists, and what it has in common with all other forms of life. An understanding of these laws and the constraints on life on Earth can then be applied to other planets, even if their physical environment is different from ours.

Dr Kershenbaum describes all the key evolutionary drivers, including natural selection, Lamarckian evolution, kin selection and game theory, then suggests that similar processes should be taking place on other planets throughout the galaxy. This makes life on other planets predictable. As this book is written for a general audience rather than an academic one, these terms are fully explained, and he never descends into too much complexity. Notwithstanding, the reader is still presented with lots of information. Dr Kershenbaum notes that Earth is absolutely teeming with life, and we are overflowing with data about it!

Those wanting to know what extraterrestrial life will look like may be disappointed as this book focuses more on behaviour, interaction, intelligence and communication rather than appearance. He does cover visual aspects such as the advantages of legs in a surface ecosystem, bilateral symmetry, the convergence of form (physical similarity between unrelated species), and the convergence of function (such as the development of the ability of flight). Where appropriate, he describes the effect of different planetary environments on familiar physical features. For example: feathers are for flying through air, not through ammonia clouds (like Jupiter), where they would become brittle & break. There is even a description of imaginary flying creatures dubbed "Fortean bladders" that could float through the dense atmosphere of planets with low gravity - on Earth, no such creatures exist.

Of greater interest to the reader will likely be the sophisticated life of alien civilisations rather than basic lifeforms. Dr Kershenbaum addresses the development of intelligence, communication methods, language and cooperation. He doubts that technology is possible without sociality; one individual, no matter how intelligent, cannot build a spaceship or a computer on their own. A chapter is devoted to each of these aspects, and he presents an interesting notional nine-point sequence of evolutionary events that takes simple early life all the way to intelligent social beings able to develop complex technology.

Obviously, some matters can only be speculated about because some questions can't be answered. Will life on other planets use DNA for its genetic material? Can alien biochemistry be based on a solvent other than water? Are two biological sexes prevalent, like life on Earth? Dr Kershenbaum notes, “Our attempt to understand what alien life is like is as much a quest to find the right questions as it is to find the right answers”.

I find that this book can sometimes come across a bit dry, devoid of the more accessible and conversational tone present in other books reviewed on this site. However, I can't help but appreciate the convincing and detailed assessment of all the key issues and the wide scope of information presented. There is a full index (hyperlinked in the Kindle version) and a great further reading list, complete with brief explanations of what each reference has to offer. This book is perfect as a springboard for further studies in astrobiology.