From Chapter 6: The Human Brain: Complexity and Mystery

The main organ in the human nervous system is the brain. Protected by the skull, its largest component is the cerebrum, which is divided into two hemispheres. Under the cerebrum is the brainstem, behind which is the cerebellum. A thick layer of brain tissue called the cerebral cortex stretches across the cerebrum. For comparison purposes, taking body size into account, the human brain is almost twice as large as that of a dolphin and three times as large as that of a chimpanzee. A critical region of the human brain is the frontal lobe of the cerebral cortex, which is utilized in executive functions such as planning, reasoning, abstract thought, and self-control. The visual lobe, responsible for processing visual sense data, is greatly enlarged in the human brain compared to other mammals. The cerebral cortex consists of neural tissue folded into ridges (gyrus) and grooves (sulcus), making it possible to fold such a large amount of tissue into the available skull volume. In other animals, brain tissue is smooth. …

Once we become conscious of our own marvelously crafted brain, we come away humbled by its mystery, deeply respectful of both its complex architecture and of what it takes for conscious and intelligent life to exist on the planet. When we add to this breathtaking picture the countless selective moves that had to occur since the birth of the universe, from the formation of galaxies and the nucleosynthesis inside stars to the first appearance of a living cell and on through all the stages of growth that formed the many branches of the “tree of life,” we are left gasping at the mystery of our existence. Who would have thought only a few decades ago that we owe the substance of our bodies to the stars? As we saw earlier, their burned-out remnants scattered 10 billion years ago into outer space to form the chemical base for life. Not only has the universe used stardust to form our brain tissue, but this bewilderingly complex lump of brain cells is alive and can produce conscious states that can even think about and reflect on these things.

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