Every living thing on the planet had parents.
This is a law of biology so fundamental that it's usually taken for granted, but it holds the key to the phenomenon known as descent with modifications, which is the mechanism of evolution. This process leaves signatures of ancestral features in the descending organisms, and so we can learn about our own bodies from studying the whole "tree of life": the way our body is constructed and the way it works; how a complete individual with lungs and heart, skull and feet, ears and eyes is assembled from the initial clump of cells.
With incredible breadth but not getting bogged down in detail, Shubin looks to fossil evidence, development of embryos and analysis of DNA to convincingly present his picture of the unity of life on Earth and the origins of our own characteristics.
As in Wislawa Szymborska's poem, "the hand that made a flint axe, and the hand that made a spaceship is a hand ne fin": and the bones in this hand are uncannily identical to the bones in a flipper of a long extinct proto-amphibian whose fossil Shubin dug out in the freezing Canadian Arctic. The chapters dealing with embryonic development and its genetic regulators as well as the ones detailing the nitty-gritty of the human ear were particularly riveting.
Both style and content would suggest that the intended audience of "Your Inner Fish" consists of young(ish) people with no knowledge of biology beyond basic school level, though I have spotted a few terms that could do with an explanation for those who might have forgotten even that. Nevertheless, it's a very accessible book: the vocabulary is as jargon-free as possible and specialist terms are introduced only when necessary, never for the sake of just presenting a label for something.
Shubin explains the physiological processes and anatomical structures in a lively, simple, easy to visualise terms and enlivens his account with jokes, anecdotes and comparisons to modern life and even pop-culture. These might be occasionally annoying but mostly are actually very useful (I will never forget that sponges can re-assemble after being put through a sieve - you need to read the book to see why it was made so memorable; and a kitchen recipe for extracting the "white glop" of DNA might come useful one day).
There is enough descriptive detail and anecdote to maintain interest, but Shubin never loses his fundamental focus on the Big Idea and there are handy summaries and brief reiterations of the key points to help the reader keep on track too.
Shubin freely draws on his own experience in the field and this personal angle provides anecdote, interest and often introduces new sections. It's interesting, well told and useful as it sheds some additional light on how the science is done in the field and in the lab. It also allows him to show how seemingly obscure details that individual scientist tend to study (e.g. teeth in proto-mammals who lived millions of years ago) are meaningful in the greater story of life on Earth and can help understand how our own human bodies evolved, how they are constructed and how they work.
The title captures perfectly the underlying idea of the whole book: our own bodies carry an inheritance that goes to the very beginning of life on Earth. The fundamental unity of all living (and now extinct) organisms is shown again and again; while clues to better understanding of human anatomy and physiology can be found in simpler vertebrates (e.g. sharks), other animals (fruit flies) and even sponges.
I always find it rather wonderful how the most modern, cutting age science can provide not only knowledge about the nature of the world, but also demonstrate how we are a part of it. A brain that can question this connection is, luckily, the same brain that is capable of understanding at least a fraction of the history of its own emergence from the primeval slime of first bacteria.
Recommended, especially for those with little knowledge of natural science and for those who were ever, even momentarily, for a single moment, confused by the ideas of the so called theory of the so called "intelligent design".
Allen Lane hardback, 240 pages