This book is not what I expected, but quite pleasurable to read nonetheless. Your Inner Fish does not detail the ichthyologic nature of the human body. Rather, it explores how fish moved onto land, where many now-ubiquitous adaptations came from, and how scientists figured it out.
Dr. Shubin begins with the story we all came to hear: how his team of paleontologists discovered Tiktaalik Roseae. This ancient, shallow-water fish Tiktaalik is an important transitional fossil because it was one of the first discovered with rudimentary hands. Biologists comparing the limbs of species noticed pattern in the limbs of land animals as far back as the mid-1800s. This patter held only for land-adapted species—reptiles, amphibians, mammals (including aquatic mammals that returned to the seas).
For a long time, it was believed that fish don’t exhibit this pattern. Then lungfish were discovered: living fossils which exemplify, in some ways, the transition from ocean to land. As their name implies, they possess basic lungs, and, interestingly, the beginnings of limbs.
Tiktaalik was an improvement on the lungfish. It had a flat head, for swimming in shallow water, and fin bones that show the beginning of a wrist. Together, we see why fins evolved into arms: shallow water fish needed to do pushups. In their fish-eat-fish world, the ability to push oneself through extra-shallow patches was likely a critical advantage.
Let me tell you, exercising seems a lot less mundane when you consider that your lungfish ancestors did it to survive. That’s what your arms evolved to do. It’s only more recently we found further applications for them.
Throughout this book, Shubin is trying to explain how scientists managed to figure out our evolutionary history. He has perhaps a unique perspective to explain this process, as a paleontologist turned anatomy professor. Knowing what came before helps explain the ways in which earlier species were contorted to become the ones we see today.
Comparative anatomy and the fossil record tell us a lot about how modern species came to be. But genetics also offers considerable insight. Looking at the differences between genomes can tell us a lot about how recently certain categories of features evolved. In many cases, we can take genes from mice or fish and insert them into the DNA of invertebrates like fruit flies and get the same result. Such experiments are strong evidence that features like body plans and eyes evolved a really long time ago.
To be clear, there’s a lot of uncertainty which can probably never be resolved. We can prod algae in tanks to evolve the beginnings of multicellular bonding, but we have no idea if that particular direction is the one that our forerunners took.
Nevertheless, Your Inner Fish gives a good overview of how bacteria became bugs and fish, and how those bugs and fish became the bugs, fish, and people alive today. I certainly came away with an improved picture of how weird our bodies are and their many imperfections, though far from the whole picture. My curious is fairly sated, however—I’ve no plans to read the kinds of human anatomy texts I would need to really appreciate the magnitude of making men from microbes.
All told, I’d recommend Your Inner Fish as an entertaining and informative read about how human beings came to be. Neil Shubin has packed a lot of interesting scientific research into it, and with the exception of an example about hypothetical clown people in the final chapter, does a pretty good job of explaining it clearly. Definitely worth your time if the history of life on Earth intrigues you.