Free Last Ape Standing: The Seven-Million-Year Story of How and Why We Survived by Chip Walter

sensitive to light, possessed rudimentary sets of eyes, and responded to, rather than ignored, changes in temperature—all radical innovations in their time. Even today they remain expert at sensing food, and then making their way with uncanny determination to it, while other metazoans (corals, for example) generally take a more leisurely approach to their cuisine, waiting for it to find them rather than the other way around.

    Planaria—the Einstein of the Day
    Among the cellular innovations that made an ancient flatworm’s brain possible was a protoneuron called a ganglion cell. These are clustered in the head of the worm and then connected to twin nerve cords that run in parallel down the length of its body so that certain experiences sensed alongside it can be transmitted to the flatworm’s brain for some metazoan cogitation. All the brains that evolution has so far contrived rest on this tiny foundation. So for the best ideas youhad today you can thank the determined metazoan that looks something like a squished noodle. 2
    The purpose of brains generally is to organize the waves of sensory phenomena that nature’s cerebrally gifted creatures experience. Their job is to filter the world’s chaos effectively enough to avoid, for as long as possible, the disagreeable experience of death. A direct correlation exists between survival and how well a brain maps the world around it. The more accurately it can correlate, the more likely it will survive danger, discover rewards, and keep its owner among the living.
    At the heart of every brain are its neurons, the specialized cells that make possible our brand of thinking, feeling, seeing, moving, and nearly everything else important to us. There are over 150 different kinds of neurons, making them the most diverse cell type in the human body. To support their greedy habit of consuming large quantities of energy, they are surrounded by clusters of glial cells, which serve as doting nannies busily shuttling nutrients and oxygen to them while fetching away debris and generally working to keep the neurons fresh and firing. Each of us carries roughly a hundred billion neurons clustered jellylike inside our skulls (coincidentally about the same number as stars cosmologists believe populate the Milky Way galaxy). Every one of them is supported by ten to fifty indulgent glial cells.
    This makes our brains a remarkable and mysterious place still well beyond the comprehension of the thing itself (a fascinating irony), but the cerebral cortex of a growing human child is more remarkable still. Only four weeks after a human sperm and egg successfully find one another, when we are still embryos no larger than a quarter, clusters of neurons that will eventually become our brain are replicating at the rate of 250,000 every minute, furious by any standard. Around this time, a bumpy neural tube that looks suspiciously similar to a glowworm has begun to take shape. Over the next several weeks four buds within the tube will begin developing into key areas of the brain: the olfactory forebrain and limbic system—the seat of many of our primal emotions; the visual and auditory midbrain, which governs sight, hearing and speech; the brain stem, which controls autonomic bodily functions such as breathing and heartbeat; and the spinal cord, the trunk line for brain–body communication. Two weeks later a fifth cluster of neurons begins to blossom into the frontal, parietal, occipital, and temporal lobes of the cerebral cortex, where so many exclusively human brain functions reside. 3
    The brain constructs itself this way, with neurons ebulliently proliferating, and then, like the rest of the cells in the embryonic body, they march off to undertake their genetically preordained duties. During this process and throughout our lives, every cell in the body communicates. It is in all cells’ DNA, not to mention our best interests, to reach out and touch one another, mostly by exchanging proteins and