Joseph makes the point that the human brain still contains parts that were used by animals that lived hundreds of million of years ago. In other words, we share parts of the brain of many other animals, and, ultimately, one can say that all animals are "linked" by the "collectively shared unconscious" Joseph calls the human body a "living museum" because it contains so many remnants of ancient organs.

This is also visible in language: while we have developed sophisticated spoken languages, we still use gestures, that are presumably an archaic form of communication. Old and new languages coexist. We often communicate unconsciously to other beings precisely because we still have, like it or not, the old languages. For example, a facial expression is enough to communicate our state of mind.

Neurons (nerve cells) first appeared 700 million years ago. When neurons got connected, the first brain was born. That being was capable of controlling and coordinating its body.

Joseph believes that the first major grouping of neurons occurred among olfactory cells, that originally may have been external cells. Eventually they migrated inside the body and created am olfactory lobe. Later, a similar fate turned visual cells into the visual lobe. The growth of these two lobes over evolutionary time eventually yielded the brain as we know it (the two hemispheres).

The olfactory lobe also evolved into the limbic lobe, that still controls many of the "instinctive" activities (in both humans and other animals). The cells of the limbic lobe created more and more layers, and eventually created the cortex. Thus the fundamental structure of the modern human brain evolved from the olfactory lobe.

Joseph then analyzes the various forms of communication that are crucial to our understanding of the world, the languages of the body. Again, odors seem to play an important role. The nose contains the most exposed (unprotected) neurons of the human body. The mucosa of the nose is directly connected to the hippocampus and the amygdala, which are instrumental in creating memories. It is likely that living beings developed the ability to analyze chemicals (odors) in order to understand changes in the environment and to sense other beings (in fact, our bodies still excrete odor-generating chemicals from the skin). Odors, after all, control sex and aggression and many other basic activities of most species.

Another key component of an individual's life is the sense of touch. The limbic system motivates the organism to touch and be touched, and, again, touching becomes an important form of communication. Contact can deliver love, comfort, fear, etc. Thus Joseph unveils the logic of kissing.

Another widespread language of the body is the language of the body in motion. Movement (for example, the dance of the bees) is another form of communication. A human dancing is likely to be a more sophisticated version of this form of communication.

Then there is the universal language of signs and gestures. Again, Joseph shows that the language of gestures has a neural foundation, and that it is shared with many animals.

Joseph then enters the realm of higher cognitive faculties, starting with the evolution of reading writing and arithmetic. Joseph shows how the evolution of the inferior parietal lobe enabled language, tool making and art itself. It enabled us, in other words, to create visual symbols. It also enabled us to create verbal symbols, i.e. of writing.

The inferior parietal lobe (of the left hemisphere) allows the brain to classify and label things. This is the prerequisite to forming concepts and to "abstracting" in general. Surprisingly, this is also the same organ that enables meaningful manual gesturing. Thus the evolution of writing is somehow related (neurally speaking) to manual gesturing. The inferior parietal lobe was one of the last organs of the brain to evolve, and it is still one of the last organs to mature in the child (which explains why children have to wait a few years before they can write and do math). This lobe is much more developed in humans than in other animals (and non-existent in most). The neurons of this lobe are somewhat unique in that they are "multimodal": they are capable of simultaneously processing different kinds of inputs (visual, auditory, movement, etc). They are also massively connected to the neocortex., precisely to three key regions for visual, auditory and somesthetic processing. Their structure and location makes them uniquely fit to handle and create multiple associations. It is probably this lobe that enables us to understand a word as both an image, a function, a name and many other things at the same time.

Joseph claims that the emotional aspect of speaking is the original one: the motivation to speak comes from the limbic system, the archaic part of the brain that deals with emotions, and that we share with other mammals. The limbic system embodies a universal language that we all understand, a primitive language made of calls and cries. Each species has its own, but within a species all members understand it. Joseph believes that at this stage the "vocal" hemisphere is the right one. Only later, after a few months, does the left hemisphere impose structure to the vocalizing and thus become dominant in language.

Along the way, Joseph explains the neural foundations of simple human phenomena, such as why women talk more than men and why human music has rhythm.

Joseph presents a view of the brain as three minds (the two hemispheres and the limbic system) that largely operate independently. Brain functions turn out to be an odd arrangement of tasks split among these three minds. But it is precisely this asymmetric distribution of tasks that originates human life as we know it, from art to war.