Huxley challenged this view; his own dissections failed to turn up the hippocampus minor. The two titans clashed over this for decades. The controversy occupied center stage in the Victorian press, creating the kind of media sensation that is reserved these days for the likes of Washington sex scandals. A parody of the hippocampus minor debate, published in Charles Kingsley’s children’s book The Water-Babies, captures the spirit of the times:
[Huxley] held very strange theories about a good many things. Hedeclared that apes had hippopotamus majors [sic] in their brains just as men have. Which was a shocking thing to say; for, if it were so, what would become of the faith, hope, and charity of immortal millions? You may think that there are other more important differences between you and an ape, such as being able to speak, and make machines, and know right from wrong, and say your prayers, and other little matters of that kind; but that is a child’s fancy, my dear. Nothing is to be depended on but the great hippopotamus test. If you have a hippopotamus major in your brain, you are no ape, though you had four hands, no feet, and were more apish than the apes of all aperies.
Joining the fray was Bishop Samuel Wilberforce, a staunch creationist who often relied on Owen’s anatomical observations to challenge Darwin’s theory. The battle raged on for twenty years until, tragically, Wilberforce was thrown off a horse and died instantly when his head hit the pavement. It is said that Huxley was sipping his cognac at the Athenaeum in London when the news reached him. He wryly quipped to the reporter, “At long last the Bishop’s brain has come into contact with hard reality, and the result has been fatal.”
Modern biology has amply demonstrated that Owen was wrong: There is no hippocampus minor, no sudden discontinuity between apes and us. The view that we are special is generally thought to be held only by creationist zealots and religious fundamentalists. Yet I am prepared to defend the somewhat radical view that on this particular issue Owen was right after all—although for reasons entirely different from those he had in mind. Owen was correct in asserting that the human brain—unlike, say, the human liver or heart—is indeed unique and distinct from that of the ape by a huge gap. But this view is entirely compatible with Huxley and Darwin’s claim that our brain evolved piecemeal, sans divine intervention, over millions of years.
But if this is so, you may wonder, where does our uniqueness come from? As Shakespeare and Parmenides had already stated long before Darwin, nothing can come of nothing.
It is a common fallacy to assume that gradual, small changes can only engender gradual, incremental results. But this is linear thinking, which seems to be our default mode for thinking about the world. This may be due to the simple fact that most of the phenomena that are perceptible to humans, at everyday human scales of time and magnitude and within the limited scope of our naked senses, tend to follow linear trends. Two stones feel twice as heavy as one stone. It takes three times as much food to feed three times as many people. And so on. But outside of the sphere of practical human concerns, nature is full of nonlinear phenomena. Highly complex processes can emerge from deceptively simple rules or parts, and small changes in one underlying factor of a complex system can engender radical, qualitative shifts in other factors that depend on it.
Think of this very simple example: Imagine you have block of ice in front of you and you are gradually warming it up: 20 degrees Fahrenheit…21 degrees…22 degrees…Most of the time, heating the ice up by one more degree doesn’t have any interesting effect: all you have that you didn’t have a minute ago is a slightly warmer block of ice. But then you come to 32 degrees Fahrenheit. As soon as you reach this critical temperature, you see an abrupt, dramatic change. The crystalline structure of the ice decoheres, and suddenly the water molecules start slipping and flowing around each other freely. Your frozen water has turned into liquid water, thanks to that one critical degree of heat energy. At that key point, incremental changes stopped having incremental effects, and precipitated a sudden qualitative change called a phase transition.
Nature is full of phase transitions. Frozen water to liquid water is one. Liquid water to gaseous water (steam) is another. But they are not confined to chemistry examples. They can occur in social systems, for example, where millions of individual decisions or attitudes can interact to rapidly shift the entire system into a new balance. Phase transitions are afoot during speculative bubbles, stock market crashes, and spontaneous traffic jams. On a more positive note, they were on display in the breakup of the Soviet Bloc and the exponential rise of the Internet.
I would even suggest that phase transitions may apply to human origins. Over the millions of years that led up to Homo sapiens, natural selection continued to tinker with the brains of our ancestors in the normal evolutionary fashion—which is to say, gradual and piecemeaclass="underline" a dime-sized expansion of the cortex here, a 5 percent thickening of the fiber tract connecting two structures there, and so on for countless generations. With each new generation, the results of these slight neural improvements were apes who were slightly better at various things: slightly defter at wielding sticks and stones; slightly cleverer at social scheming, wheeling and dealing; slightly more foresightful about the behaviors of game or the portents of weather and season; slightly better at remembering the distant past and seeing connections to the present.
Then sometime about a hundred and fifty thousand years ago there was an explosive development of certain key brain structures and functions whose fortuitous combinations resulted in the mental abilities that make us special in the sense that I am arguing for. We went through a mental phase transition. All the same old parts were there, but they started working together in new ways that were far more than the sum of their parts. This transition brought us things like full-fledged human language, artistic and religious sensibilities, and consciousness and self-awareness. Within the space of perhaps thirty thousand years we began to build our own shelters, stitch hides and furs into garments, create shell jewelry and rock paintings, and carve flutes out of bones. We were more or less finished with genetic evolution, but had embarked on a much (much!) faster-paced form of evolution that acted not on genes but on culture.
And just what structural brain improvements were the keys to all of this? I will be happy to explain. But before I do that, I should give you a survey of brain anatomy so you can best appreciate the answer.
A Brief Tour of Your Brain
The human brain is made up of about 100 billion nerve cells, or neurons (Figure Int.1). Neurons “talk” to each other through threadlike fibers that alternately resemble dense, twiggy thickets (dendrites) and long, sinuous transmission cables (axons). Each neuron makes from one thousand to ten thousand contacts with other neurons. These points of contact, called synapses, are where information gets shared between neurons. Each synapse can be excitatory or inhibitory, and at any given moment can be on or off. With all these permutations the number of possible brain states is staggeringly vast; in fact, it easily exceeds the number of elementary particles in the known universe.
Given this bewildering complexity, it’s hardly surprising that medical students find neuroanatomy tough going. There are almost a hundred structures to reckon with, most of them with arcane-sounding names. The fimbria. The fornix. The indusium griseum. The locus coeruleus. The nucleus motoris dissipatus formationis of Riley. The medulla oblongata. I must say, I love the way these Latin names roll off the tongue. Meh-dull-a oblong-gah-ta! My favorite is the substantia innominata, which literally means “substance without a name.” And the smallest muscle in the body, which is used to abduct the little toe, is the abductor ossis metatarsi digiti quinti minimi. I think it sounds like a poem. (With the first wave of the Harry Potter generation now coming up through medical school, perhaps soon we’ll finally start hearing these terms pronounced with more of the relish they deserve.)