The work traces three lines of evidence that Shubin offers as a way to better understand our own origins - fossils, genes, and embryos. Shubin builds our understanding in the book's first pages of how knowledge about anatomy and geology are necessary in the use of fossils to understand the evolution of species.
The order of fossils in the world's rocks is powerful evidence of our connections to the rest of life. If, digging in 600-million-year-old rocks, we found the earliest jellyfish lying next to the skeleton of a woodchuck, then we would have to rewrite our text. The woodchuck would have appeared earlier in the fossil record than the first mammal, reptile, or even fish - before even the first worm. Moreover, our ancient woodchuck would tell us that much of what we think we know about the history of the earth and life on it is wrong. Despite more than 150 years of people looking for fossils - on every continent of earth and in virtually every rock layer that is accessible - this observation has never been made.Once a certain body of information has been amassed about the age of rocks and the structure of the skeletons of ancient creatures, a scientist can begin to make predictions about the layers of rock in which they are likely to find a particular kind of fossil - even if that fossil has yet to be discovered. This is, in fact, exactly what Shubin and his team did:
It took us six years to find it, but this fossil confirmed a prediction of paleontology: not only was the new fish an intermediate between two different kinds of animal, but we had found it also in the right time period in earth's history and in the right ancient environment...Shubin's ushers us into the world of genes building the reader's understanding with simple, clear language. He does the same for developmental embryology, telling the story of how multi-celled creatures like the sponge or us humans evolved from single celled ones with the advent of intra-cellular communication and substances like collagens and proteoglycans - the glue that hold cells together. My favorite story in the book was about single-celled creatures known as choanoflagellates, their similarity to a particular type of cell in the sponge, many of which assemble to form the prototype of a mouth, and the genetic evidence to suggest that structures of multiple cells in bodies evolved from the collaboration of single-celled creatures in just this way. What are the advantages of the body plans that evolved since algae and single celled flagellates? What are the liabilities, since we all know that single celled creatures are still in abundance and there is ample evidence for our imperfections in thrombosis, and choking (one could not call the fact that we use the same tube to both inhale and swallow food particularly intelligent design.
Darwin's theory allows us to make very precise predictions.
Shubin is an amusing teacher, giving us a primer in how to extract DNA with just a kitchen blender, some dish soap, and rubbing alcohol. Talking about the origin of hiccups and hernias as misbegotten legacies of evolution, and offering a wonderful lesson in heredity with a family tree of clowns that arises from run-of-the-mill humans with the single mutation of a red rubber nose, followed in the next generation by floppy feet, and then orange curly hair. Once he has laid the groundwork, Shubin then launches into his point about what information we can derive from the family tree of a species:
The real power of this family tree lies in the predictions it allows us to make... We can now... confidently reconstruct the relationships among long-dead animals and the bodies and genes of recent ones[.] We look for the signature of descent with modification, we add characteristics, we evaluate the quality of the evidence, and we assess the degree to which our groups are represented in the fossil record.Shubin is an effective teacher because he doesn't forget that to communicate his subject is more than impressing us with his knowledge, it is allowing us to see his wonder at the world, the vulnerability he feels when he perceives we have learned something new about who we are, this permits the reader to share his passion for his subject without becoming experts ourselves and he accomplishes this most effectively in Your Inner Fish.