As David Eagleman describes it in his wonderful book Incognito: Your brain is built of cells called neurons and glia — hundreds of billions of them. Each one of them is as complex as a city. . . . The cells [neurons] are connected in a network of such staggering complexity that it bankrupts human language and necessitates new strains of mathematics. A typical neuron makes about ten thousand connections to neighboring neurons. Given billions of neurons, this means that there are as many connections in a single cubic centimeter of brain tissue as there are stars in the Milky Way galaxy.

God has given to every one of us more than fourteen billion cells and connections in our brain. Now why would God give us such a complex organ system unless He expects us to use it?

In fact, we’re not smart and we have bodies — we’re smart because we have bodies.7 The heart has about 40,000 neurons that play a central role in shaping emotion, perception, and decision making. The stomach and intestines complete this network, containing more than 500 million nerve cells, 100 million neurons, 30 different neurotransmitters, and 90 percent of the body’s supply of serotonin (one of the major neurochemicals responsible for mood and well-being). This “second brain,” as scientists have dubbed it, lends some empirical support to the persistent notion of gut instinct.

In its evolution from a more primitive nervous system, the brain, as an organ with ten or more billion neurons and many more connections between them must have changed and grown as a result of many accidents.

Shall we appreciate any less the beauty of nature because its harmony is unplanned? And shall the potential of mind cease to inspire our awe and fear because several billion neurons reside in our skulls?

In the old times of which I have spoken, they desired to make all men think exactly alike. All the mechanical ingenuity of the world cannot make two clocks run exactly alike, and how are you going to make hundreds of millions of people, differing in brain and disposition, in education and aspiration, in conditions and surroundings, each clad in a living robe of passionate flesh — how are you going to make them think and feel alike? If there is an infinite god, one who made us, and wishes us to think alike, why did he give a spoonful of brains to one, and a magnificent intellectual development to another? Why is it that we have all degrees of intelligence, from orthodoxy to genius, if it was intended that all should think and feel alike?

Take disintegration far enough and you get a new form of integration. I tend to see all this in neural terms. It doesn’t matter how big your brain is, or how many cells or neurons in it, what matters is the synaptic fusions, the connections that determine how intelligent you are. As with the individual, so with the macrocosm. That’s how the kind of society I live in works, me and my friends and my contacts, we don’t work in any hierarchical sense. No one wants a boss, to be a boss, to work under a boss. The people you like working with are the people you respect as individuals.

"If you plug in the neocortex ratio for Homo sapiens, you get a group estimate of 147.8-or roughly 150. "The figure 150 seems to represent the maximum number of individuals with whom we can have a genuinely social relationship, the kind of relationship that goes with knowing who they are and how they relate to us.

There is no limit to the power of the human mind. The more concentrated it is, the more power is brought to bear on one point

Research shows that on any given day, the average person thinks somewhere between 50,000 and 60,000 thoughts. The problem is that ninety-five percent of our thoughts are the same as the ones we thought the day before, and the day before that, and the day before that.

The web holds about a trillion pages. The human brain holds about a hundred billion neurons. Each biological neuron sprouts synaptic links to thousands of other neurons, while each web page on average links to 60 other pages. That adds up to a trillion “synapses” between the static pages on the web. The human brain has about 100 times that number of links — but brains are not doubling in size every few years. The global machine is.

Human intellect, on the other hand, is expressed through a subatomic network of circuits contained within roughly three pounds of cerebral tissue, evolved over hundreds of millions of years into the most energy-efficient, generalized self-programming array currently known, powered by a mere four hundred twenty calories per day — or

This adult male. This person on earth. Ten billion nerve cells. Ten pints of blood pumped by ten ounces of heart. This object took three billion years to emerge.

Cell differentiation can turn neurons into everything from clocks that control circadian rhythms to photoreceptors that convert light into electrical-chemical impulses or decision makers that tally votes and decide courses of action. In the retina (often used as a case study because it can be directly and naturally stimulated), there are at least fifty different kinds of neurons specialized to different tasks, such as looking for motion, recognizing colors, detecting objects in low light, and measuring brightness and contrast. In the brain as a whole, there may be as many as 10,000 different kinds of neurons, each contributing to a different aspect of mental life.