Your Inner Fish Summary

Neil Shubin

Your Inner Fish

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Your Inner Fish Summary

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Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body is a 2008 non-fiction science book by American paleontologist and evolutionary biologist Neil Shubin. Illustrating the subject of evolution with humor and easy-to-read language, Shubin explores the details of how the human body evolved into its current form. Starting with the earliest fish and later land-dwelling creatures, Shubin tracks how the human body bears basic resemblances to these earliest ancestors of life. Each chapter focuses on a different part of the human body and how traces of its structure can be found in creatures that lived eons ago. Through exploring fossils and the DNA of ancient creatures, Shubin finds genetic links even between humans and such primitive creatures as worms and bacteria. Emphasizing the theme that all creatures—from humans to the earliest life in the primordial Earth—are all part of the same web of life, Your Inner Fish is one of the most popular and critically acclaimed works of scientific non-fiction in the 21st century.

Broken up into eleven chapters, Your Inner Fish begins in Chapter One by exploring what all species have in common with humans. He compares it to exploring a zoo and finding common ground even with the fish. After all, all animals, even fish and insects, have heads that are remarkably similar to those of humans. The chapter ends by illustrating the evolution of arm bones—from primitive fish fins designed only for propelling to the multi-use limbs of humans. Chapter Two expands on this theme, focusing exclusively on the evolution of the arm and contrasting the human and ape arm with the fins of fish as well as with the wings of birds, showing how the general structure is near-identical. Chapter Three delves deeper into the building blocks of human design—DNA itself—and looks at the makeup of human DNA, contrasting it with the DNA of birds and even bacteria. He also looks at in-utero development, illustrating the developmental process of the human arm with that of the chicken’s wing.

Chapter Four looks at teeth, exploring the different purposes of teeth for herbivores, carnivores, and omnivores (including humans). As dinosaur teeth have been very well preserved, Shubin is able to look at these fossils and find remarkable similarities between the varied types of teeth that humans have, and the more specific teeth possessed by dinosaurs, which ate only one thing. Chapter Five focuses on the head, the one body structure held by almost every single land organism on planet Earth. He looks at the structure of the skull and how it’s usually constructed of plates, blocks, and rods. Jaws, ears, larynxes, and throats are also all constructed similarly across species, and their evolution can be traced from gills in fish. Even the cranial nerves are similar in most species. Shubin looks at sea worms, which do not have traditional heads, and finds primitive parallels there as well. In Chapter Six, Shubin looks at less traditional organisms, such as sea anemones, that do not have the structures that humans have. Here, however, he finds parallels between their body construction and that of early embryos before the human body fully forms.

Chapter Seven takes a wider look, tracking the timeline of life on Earth and looking at how sea sponges, one of the earliest forms of life, displayed some similar characteristics to human evolution, particularly in their reproductive methods. Chapters Eight and Nine are short, and focus on two specific organs in the human body: the eyes and the nostrils. Sight and smell are among the most important defense techniques in the animal kingdom, and from the earliest life forms, animals used them to survive. Some animals, such as moles, are born without one of these senses due to their environment, and so compensate with an enhanced version of one of the other senses. Eye and nostril design is shown to be remarkably similar across species, even in comparisons between a human and a jawless fish like a lamprey. Chapter Ten focuses on another sense, hearing, and the incredibly complex structure of the human ear. The inner ear is shown to be the most ancient structure in the system of hearing, and a similar structure can be found in creatures with no outer ear. Chapter Eleven brings it all together, showing the natural way evolution happens over generations and how new adaptations and enhancements happen to existing body structures. He concludes by re-emphasizing that we can learn a lot about our own bodies and the way they are evolving by looking at the creatures that came before us, both those still here and those that have passed into extinction.

Neil Shubin is a world-renowned paleontologist and evolutionary biologist, as well as a popular science writer. He is currently a professor and associate dean at the University of Chicago, as well as the Provost of the Field Museum of Natural History. In addition to Your Inner Fish, he is the author of the 2013 book The Universe Within: Discovering the Common History of Rocks, Planets, and People, which deals with similar themes and expands its focus to the construction of Earth and the universe. He is perhaps best known for his discovery of Tiktaalik roseae, an extinct fish that is believed to be an ancestor of the earliest amphibians.