Shubin starts the book with a timeline of the scientists who pioneered the theory that all animals share the same design pattern, notably Richard Owen (a Darwin contemporary), who saw a pattern in the skeletons of all vertebrates, and Jenny Clack, who in 1988 realized that the earliest limbs arose to swim rather than to walk.

The book is mostly organized in eight chapters each focusing on one element of human anatomy: hands, teeth, head, the gene that generates the body, constituent molecules, the sense of smell, vision, and ears. Shubin first show how fish fins became limbs. A key moment was when In the 1990s Cliff Tabin discovered the genes that control the "zone of polarising activity" (ZPA) on embryonic limb buds, and indirectly found a similarity between flies and chickens. And then Shubin's collaborators discovered that similar genes "build" both fins and limbs. Teeth and bones are made mostly of hydroxiapatite (a calcium phosphate mineral). By studying how ancient living beings assembled that material, Shubin concludes that teeth emerged first to bite and then teeth evolved into bones to protect the body. The structure of the skull was first envisioned in 1790 by Johannes Goethe (the poet and novelist): the skull is basically created by curved vertebrae that create a vault to protect the brain. The skull reuses the schema of the vertebrae. The very complex and convoluted cranial nerves of the human head can be explained as arches that have been twisted. Every skull of every animal follows the same pattern. In 1991 Linda Buck and Richard Axel discovered the genes that give us the sense of smell, and these genes account for 3% of the genomes of a mammal, about a thousand genes, although Yoav Gilad has discovered that many of these "odor" genes are no longer functioning in animals that enjoy color vision (presumably because vision genes have become more important). Every animal uses the same light-capturing molecule, opsin, to deal with light. In 2001 Detlev Arendt identified an animal that has both the eyes of vertebrate animals and the eye of invertebrate animals, the polychaetes (a very primitive worm). In the 1900s Mildred Hoge discovered the gene responsible for the development of the eye. She found eyeless flies and realized that their "blindness" was due to a mutation of that gene. In the 1990s Walter Gehring's team transplanted the eye gene on different places of the fly and made eyes grow in all these places. This happened even when he transplanted the eye gene of a mouse into parts of a fly: a fly eye would grow. Shubin notices that the gene responsible for the eye and the gene responsible for the ear may have had a common ancestor: the most ancient animals on Earth are the jellyfish and the sponges, born before those genes evolved, and the jellyfish's eye gene is a mix of the modern eye gene and the modern ear gene (Pax 6 and Pax 2). There are many more similarities across species in these chapters that illustrate Shubin's general thesis that all bodies share the same "plan".

Along the way we are introduced to substances that are not famous but are crucial to our existence. For example, bones and teeth are made of hydroxiapatite (a calcium phosphate mineral). The cells of all animals with bodies are separated by molecules such as collagens (90% of the body's proteins by weight) and proteoglycans, molecules used by cells to communicate with each other.

Two central chapters are particularly interesting for a general theory of how evolution led to bodies. Christian Pander discovered the three germ layers (endoderm, ectoderm and mesoderm) in the chicken embryo that originate all organs of the body of the chicken. Karl Ernst von Baer realized that exact same process creates the bodies of all other animals. In 1924 Hans Spemann's student Hilde Mangold discovered the "organizer", a small patch of tissue in the embryo that determines the general structure of the body: transplant the organizer of an embryo into another embryo and you get twin embryos. In the 1980s geneticists discovered that the organizer's function is due to Hox genes (the "homeobox" discovered by Gehring's team in 1983), which are at work in every animal with a body. In 1993 Richard Harland discovered the Noggin protein is used by the organizer, and the same kind of Noggin gene has been discovered in the sea anenome. These body-building genes lend themselves to scary experiments: you can cause the organ of an animal to grow on another animal. There is therefore a common way that life organizes itself into bodies, regardless of what body we're talking about.

For 3.5 billion years life meant microbes, no bodies. Multicelled organisms began to populate the sea about 600 million years ago (at the end of the Precambrian), and over the span of a few million years a lot of different bodies appeared. The cells of their bodies were organized according to some patterns, and differet parts had specialized functions. Nicole King, who studies choanoflagellates, found that the genes that build bodies are shared with some microbes ("A bacterial sulfonolipid triggers multicellular development in the closest living relatives of animals", 2012), so the appropriate genes were around much earlier than the first bodies. As Martin Boraas has shown experimentally, a body offers protection from predators while increasing the chances of becoming one: i.e. a body helps eat other bodies and protect from other bodies. (Boraas created "proto-bodies" from "no-bodies" - "Phagotrophy by a flagellate selects for colonial prey", 1998). Shubin believes that those genes needed the right environment to express themselves, namely an environment rich in oxygen. So Shubin concludes that at some point microbes learned to eat each other, a fact that made bodies an evolutionary advantage, and then 600 million years ago the atmosphere had enough oxygen to make that evolutionary advantage physically possible. The genes to create bodies were already there, since the beginning.

The personal anecdotes can get a bit tedious and distract form the main discussion (the book could have been half the size), but the book is overall an entertaining and stunning summary of what we know about how bodies evolved.

It's a pity that notes are confined at the end of the book. Most readers will never check the notes, which instead contain valuable information.

Shubin continued the story in the equally engaging book "The Universe Within" (2013).

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