Chapter 1 - Brain

Six billion years ago, the atoms now comprising your brain were not only dissociated, they were scattered far across the light-years of an interstellar cloud. The cloud condensed and spawned stars and their worlds. And so, eventually, the atoms of your brain-to-be found themselves on a newborn planet, third out from a youthful Sun. Earth's atmosphere evolved, becoming increasingly complex. And all of it happened on its own, in the black, blank time before there was intelligence and consciousness. Planets came from dust, life from non-life, brains from strands of biological wire.

The first nervous systems were just pathways along which signals from receptors on the outside of an animal could be routed to produce some predictable action - a retreat or an advance, depending on whether the signal meant danger or the next meal. There are hosts of creatures alive today whose "brains" are no more than this - not true brains at all, but mere conduits for signal routing. That may not seem much; a worm, for instance, can never appreciate Bach or the blues, but at least it can sense the vibrations from the feet of concert-goers nearby and burrow its way to safety.

With the worm it is all reflex and no reflection. And yet, in time, species did emerge on Earth that could do more than just respond robotically to stimuli. Brains became more complex, more capable, almost as if nature were following some preconceived scheme that would lead inevitably to intelligence.

We know, however, that this is not so. Nature follows no grand design. Individuals and species interact among themselves and with their environment; some live to spawn offspring resembling themselves and some do not. The wild card - the source of biological novelty - is genetic mutation. A mutation arises when the DNA blueprint of life is subtly altered, perhaps by being imperfectly copied or through the impact between a gene and an ultraviolet ray. Most mutations prove to be fatally flawed and vanish from the gene pool almost immediately. On rare occasions, though, a mutation comes along that adds to, or improves, what was already there. It may not initially be a big improvement, but after millions of years it is likely to be compounded into something quite astonishing.

Consider the eye, for instance, and in particular the lens of the eye. This is a fairly recent evolutionary innovation. It probably made its debut with the common ancestor present-day birds and crocodilians, a few hundred million years ago. Yet one of the most important substances in the eye lenses of birds and crocodiles - a protein called epsilon-crystallin - has been around very much longer. In fact, epsilon-crystallin is identical with an enzyme (a protein that acts as a catalyst) known as lactase dehydrogenase that is vital to the production of chemical energy in even the most primitive animals.

Somewhere along the evolutionary line, a series of mutations cropped up that caused the gene for making lactase dehydrogenase to produce large quantities of this enzyme in the tissue that would form the eye. And it happened because the chemical properties of the enzyme - its stability and behavior in light, for example - were fortuitously suitable for building a lens. In other words, it was a matter of pure luck. There was no conspiracy on nature's part to manufacture lenses. There was nothing ahead of time to say that such structures had to exist. They were discovered, stumbled upon, by nature randomly working its way through countless mutations, and chancing upon a few that happened to benefit an organism. To be able to see and, moreover, to react to what you see is an obvious advantage in the struggle to stay alive. On top of that, if you can focus on an image and thus gain a clearer view of your enemy or prey, then you improve your survival chances still further. Such a beneficial adaptation will be preserved and refined through natural selection.

And that is exactly how it was with brains. Through chance mutations and selection, the primitive neural wiring systems of some creatures long ago began to acquire little extras - a switchboard, for instance, through which all incoming, sensory data first had to pass. Such a structure offered the possibility of a more measured response; one that depended on the type and strength of the signals being picked up. The result may still have been essentially mindless - an autonomic, "knee-jerk" reaction to events outside. But it was a clear step up the scale of sophistication.

If you are a worm that can respond to vibrations by smartly wriggling underground you stand a good chance of outliving your confederates who remain on the surface to be gobbled up or trodden on. The obvious survival benefit of having even a primitive response reflex is what got the nervous system off the ground. But that is still far from consciousness as you and I know it; the multicolored, sound-filled, wonderfully detailed, emotional, meaningful experience that our brains somehow manage continuously to conjure up? What did all that come from?

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Imagine that, in front of you, are the brains of a salmon, a snake, a crow, and a dog. Quite obviously, they are different, both in size and structure. At one extreme, the fish's brain resembles a snippet of entrail; in fact, it requires a magnifying lens to be properly seen. At the other extreme, the dog's brain looks like a reduced version of our own. Taking the remaining two specimens to be intermediate stages, we can interpret the progression from fish to dog as an evolutionary sequence - a series of snapshots from the childhood photo album of the brain.

The fish's brain is no more than a minute swelling at the end of the spinal cord. Weighing less than a tenth of an ounce, it contains primarily of hindbrain (or brain stem) and midbrain, with only a tiny forebrain at the anterior. Hindbrain and midbrain together have been dubbed the neural chassis, for they are a support structure. Within them are the controls for blood circulation, respiration, reproductive functions, and self-preservation reflexes. They are the body's autopilot. But they never harbored a conscious thought. They never held a dream, or an insight, or a desire. A creature that has nothing but this neural chassis lacks any semblance of awareness as we know it.

It is the forebrain, or cerebrum, that is the seat of the mind - and all that elusive thing implies. Not least, the forebrain serves as the brain's "projection room," the place where sensory data is transformed and put on display for internal viewing. In our case, we are (or can be) actually aware of someone sitting in the projection room, watching the show. But the fish's forebrain is so tiny that it surely possesses no such feeling of inner presence. There is merely the projection room itself, and a most primitive one at that. It has only the crudest emotional fitments, with no facility for replaying the reality film or visualizing alternatives, no means of looking ahead.

As for the snake, that is perhaps further up the ladder of consciousness, for its forebrain is relatively larger - several times larger than its midbrain. So presumably it can experience a richer internal universe than any fish is able to. But there is nothing about a snake, or any other type of reptile, to suggest a highly active mind at work. A reptile can, and will, sit for hours staring blankly into space. And if nothing stimulates it - a passing dainty, the intensifying heat of a desert sun - it does nothing, absolutely nothing. A snake or lizard lacks the gumption to get up and go on its own. It may have a dim awareness of the world around it, but nevertheless it is a slave to its environment, a robot without an active mind.

So we move on to consider the brains of the crow and the dog. And with these, at last, we find evidence of some dramatic development in the higher cerebral centers. The forebrain of the bird and of the mammal are large and bulbous, and they dominate those parts concerned with autonomic functions. Interestingly, however, all of the more primitive neural components (the spinal cord, the brain stem, the midbrain, and the various subregions of these) are still present. In a sense, a dog brain (and a human brain) has a fish brain deep inside it. That is to say, an advanced brain is a primitive brain with advanced parts added on. As always, evolution has been conservative, economical, building upon what is proven to be sound rather than redesigning the whole from scratch.

Of course, it is one thing to look at a brain, and quite another to be its owner. What does it feel like to be a crow or a dog (or a dolphin or a newborn child)? We could argue at length which animals are truly conscious and which are essentially as unaware as a stone. There are some who would claim that every living thing, and indeed every thing - including stones and molecules and individual subatomic particles - has some degree of consciousness. Others might more conventionally judge, say, a bacterium and an insect to be totally unconscious, a fish marginally conscious, a dog highly conscious, and an adult human demonstrably self-conscious. The fact is, to be really sure of another's quality of awareness you would have to become it. But then "you" would no longer be "you," so, upon returning to your own mind, you would have no memories, no linguistic descriptions, nothing with which to compare this strange, new experience.

Whatever it may be, consciousness is not a thing that appears suddenly. It does not abruptly spring into being with the addition of a few extra brain cells or by climbing a few rungs of the evolutionary ladder. And yet, if...