Ramachandran begins the book by wondering which features are truly unique to the human brain. Many features of the ape brain were hijacked by evolution to produce novel functions in the human brain (a process called “exaptation”). For example, mirror neurons are responsible for human culture and ethics. Ramachandran believes that these unique traits are perfectly consistent with Darwinian evolution: millennia of gradual evolution can produce the mental equivalent of phase transitions, when suddenly a substance reorganizes itself into a different substance with different properties.

He picks three regions in the human brain that are many times larger than the corresponding areas in the chimp's brain: Wernicke's area in the left temporal lobe (where a lesion impairs the comprehension of language); the prefrontal cortex of the frontal lobe (where a lesion can totally alter the personality and obliterate any ethical sense); the right and left parietal lobes (responsible for spatial mapping and logical thinking).

The other thing that is unique to the human brain is the "mirror neurons", discovered in the mid 1990s. They fire not only when an action if performed but also when observing someone else performing that action. They allow us to understand the intentions of someone else's action and to empathyze. They de facto simulate what others are doing. Ramachandran credits mirror neurons with shifting the main driver of human evolution from the genome to culture. As culture became more and more important, evolution started selecting the brains that had the best mirror neurons. Similarly, the human brain has "canonical" neurons that fire both when we perform an action on an object and when we simply see that object. For example, some canonical neurons fire both when we grasp and object and when we see that object (in other words, they seem to fire in response to the property of "graspability", regardless of whether we actually grasp the object or not).

He then explains how he reached his conclusions by analyzing phantom limbs, a topic fully explored in his previous book, "Phantoms in the Brain". His first claim to fame was to prove that the adult brain is still capable of reorganizing. Before the 1990s a view widely held by neuroscientists was that neural connections were set during the childhood and the adult brain was a static system. In 1990 Michael Merzenich and William Jenkins proved the plasticity of the brain of adult apes. In 1994 Ramachandran himself proved the plasticity of the adult human brain. The brain is, after all, changing all the time throughout a person's life.

Vision does not happen in the eye, it happens in the brain. The human eye is not particularly special, but the brain regions that process vision are quite special: our brain has 30 visual areas whereas other mammals have a dozen or so. Ramachandran argues that the shift in diet from insects to vegetables fostered the evolution of color vision (required to recognize edible vegetables) and, at the same time, of finger agility (to pick fruit). This finger agility was then instrumental in enabling us to build and use sophisticated tools that other animals cannot even hold. At the same time vision, because it happens in the brain, allowed the human brain to evolve visual imagination. Basically, the signals coming from the eye get represented symbolically in the brain and then processed. The processing, in turn, happens based on assumptions about the world. The study of vision is therefore not only the study of the signals that come from the eye but also the study of the assumptions that underly the working of those 30 visual processing regions in the brain. The "assumptions" explain why the brain can be fooled by "optical illusions".

Unfortunately, he leaves the discussion here (i guess research is still in progress) and moves on to synesthesia. Richard Cytowic in "Synesthesia" (1989) speculated that synesthesia was the normal state in the primitive human brain, when the senses had not fully separated. Ramachandran, instead, after a lengthy discussion of how he came to recognize that synestesia is not bogus, advances the hypothesis that the cause is interference between regions of the brain specialized in different tasks. He also briefly toys with the idea that synestesia may foster creativity in artists and writers.

Mirror neurons get the lion's share of the book. They are, in the author's opinion, responsible for human civilization because they enable humans, and only humans, to transmit culture. There are a number of mysteries in the evolution of Homo Sapiens. The brain of our species was born about 200,000 years ago, but little changed in behavior until about 60,000 years ago when a sudden burst of creativity introduced art and technology. It almost feels like the human brain was busy doing something else for 140,000 years. Ramachandran mentions that Darwin explained human language as a form of sexual courtship, similar to the peacock's tail. It evolved because the best speakers were selected by women.

Mirror neurons were originally discovered by Rizzolatti in the ventral premotor cortex of monkey brains and in Broca's area of human brains (both located in the frontal lobe), and later discovered also in the inferior parietal lobe (IPL), that allows you to make sense of language (and is strategically located next to the touch, vision and hearing regions of the brain), and in the anterior cingulate cortex, that makes you feel pain. Mirror neurons de facto read other animals' and other people's minds. Ramachandran thinks that they accelerated brain evolution in humans (although he doesn't quite explain why the same mirror neurons did not accelerate brain evolution in the other apes). They allow us to figure out other people's intentions, to figure out other people's viewpoints, to imitate other people's behavior (and therefore we might not need a language organ to explain how people learn languages), and to perform abstraction (including metaphor, because they ultimately transform one dimension into another dimension). He speculates that awareness of others co-evolved with self-awareness (by making us aware of others the same mirror neurons make us aware of ourselves). He discusses whether mirror neurons are innate or learned, and concludes that they are probably both (some are hard-wired for newborns to imitate their mothers, and others are acquired later in life). And he notes that, as far as mirror neurons go, our closest relative (the animal that is best at imitating) is the orangutan, not the chimpanzee.

Ramachandran speculates that autism could be caused by malfunctioning mirror neurons.

Ramachandran thinks that there are five unique features of human language: an enormous lexicon; function words (not just sounds to signify an object or an event) such as "if ... then ..."; the capacity to refer to things that don't exist, or that existed in the past or that will exist in the future; the ability to create and understand metaphor and analogy; and its recursive structure (we can say and understand sentences such as "he thought that she thought..."). According to the US linguist Noam Chomsky and the US biologist Marc Hauser ("The faculty of language", 2002), what is unique to human language is only recursion.

Chapter 6 on the evolution of language is another favorite. Evidence from brain lesions leads Ramachandran to think that not only the brain has specialized circuits for language, but that there are probably three different specialized areas for three different tasks: lexicon, syntax and semantics. A patient with Broca's aphasia wants to convey meaning but has difficulty composing sentences. On the other hand, a patient with Wernicke's aphasia utters sentences that are well-formed, grammatically correct, but meaningless (they are also in a simplified syntax that shuns recursion). Therefore it appears that Broca's area is specialized for syntax, and Wernicke's area is specialized for semantics.

Gould, taking the view that Nature is more opportunistic than rational, thought that language did not evolve from primitive forms of communication but by accident (or, better, by exaptation) as a consequence of neural circuits that evolved for different functions. First thinking appeared and later language arose as one of its by-products.

Ramachandran too thinks that language evolved as a by-product of other features, but not quite of thinking. He suspects that language emerged out of interference inside the brain between signals that are similar.

The sound that refers to an object is similar (in some physical manner) to the image of that object that is being processed by the brain. He calls this "the synesthetic theory". The brain might "translate" an image into a sound (into a protoword) simply because the maps that represent the two are adjacent and interfere with each other in quite a natural fashion. This cross-activation would be the primal cause of our linguistic competence. Next, Broca's area indirectly relates syntax and the movements that we use to produce speech.

Hence one part of the brain puts in contact image and sound, and then another part of the brain causes those sounds to be spoken. Each of these correlations can be view as an "abstraction", which in physical terms simply means that different brain regions activate each other based on similarity of signals.

A third case of cross-activation exists. Darwin himself noted that sometimes an utterance is accompanying with a gesture. Ramachandran speculates that it could be another case of cross-activation, except this one would be due to the interaction between two motor maps. This would explain how a primordial language of gestures would evolve into a spoken language. A brain that exhibits the kind of wiring that the human brain has would naturally end up translating gestures into (spoken) words. "Abstraction" is what cross-activation looks like: those brain regions activate each other because the signals within their circuitry have a similar mathematical shape, independently of whether those signals represent an image, a sound or a movement. At the neural level they are, ultimately, just electrical waves.

This whole business of cross-activation is reminiscent of how mirror neurons link concepts across brain maps.

Ramachandran suspects that the inferior parietal lobe evolved originally for cross-modal abstraction, since it has to mediate signals coming from the touch, vision and hearing regions of the brain; and then later this feature became an independent skill, the ability to think abstract thoughts. The IPL in the right hemisphere became skilled at bodily metaphors and the IPL in the left hemisphere become good at linguistic metaphors. The original abstraction was probably the mapping of vision into gesture, and to this day half of the IPL, the supramarginal gyrus, is responsible for coordinating vision and gesture (a fundamental feature of the human brain, that allows us to build and use tools to an extent unknown in other species). The other half of the IPL, the angular gyrus, found by accident (by exaptation) that this same process is useful to find similarities among different domains, e.g. for metaphorical thinking.

Initially, the human brain may have been more interested in making and using tools, and therefore evolved the skills to relate vision and gesture. By exaptation, this brain function ended up also being "translated" into the domain of communication. Is this is indeed the case, then the whole process of building tools out of parts could be the precursor of and the indirect cause for the tree structure of linguistic syntax: sentences too are constructed out of parts. The original language may have been the language of building tools, not the language of speaking words.

One chapter investigates art and the aesthetic sense. Here the neuroscientist gets in trouble because he tries to define something that has been shifting over the millennia, the centuries and the decades. What we call "art" today is not what they called "art" centuries ago or even a few decades ago. However, he comes up with a few "universal" rules that are supposed to explain why we find something beautiful. As for abstract art, he thinks that an explanation can be found in ethology, in the fact that every species tends to over-react when exposed to what he calls "ultranormal stimuli", and abstract art could be just that for Homo Sapiens. However, this unconvincing chapter contains one of the best passages in the entire book, which i take the liberty to quote verbatim:

Finally, a fourth, less prosaic reason for art's timeless appeal may be that it speaks an oneiric, right-hemisphere-based language that is unintelligible-alien, even-to the more literal-minded left hemisphere. Art conveys nuances of meaning and subtleties of mood that can only be dimly apprehended or conveyed through spoken language. The neural codes used by the two hemispheres for representing higher cognitive functions may be utterly different. Perhaps art facilitates communion between these two modes of thinking that would otherwise remain mutually unintelligible and walled off. Perhaps emotions also need a virtual reality rehearsal to increase their range and subtlety for future use, just as we engage in athletics for motor rehearsal and frown over crossword puzzles or ponder over Godel's theorem for intellectual invigoration.

Just like in his previous book, "Phantoms in the Brain", the narrative is driven by neurological cases. This is particularly true of the final chapter, where a variety of neurological conditions are used to explain that the self is probably more composite than we think (an opinion shared by the philosopher Daniel Dennett). Ramachandran takes for granted that only humans are self-conscious and therefore his search for the origins of the self focuses on the brain regions that are unique to humans. That's a crucial postulate that i am not sure i share.