Chapter 10
THE PREREQUISITES
What biological features made humans capable of civilization?
10.1 The Body
Start with the hardware.
Human bodies differ from other ape bodies in ways that matter for civilization. Not all the differences are obvious. Some seemed insignificant until we understood their consequences.
Bipedalism. Humans walk upright on two legs. This seems unremarkable—we’ve always done it—but it’s actually rare. No other primate is fully bipedal. The anatomical changes required were extensive: reshaped pelvis, rebalanced spine, repositioned foramen magnum (the hole where the spinal cord enters the skull).
The consequences were profound. Walking upright freed the hands. Hands that don’t need to support locomotion can carry things—food, tools, infants. They can manipulate objects while moving. The freed hands became available for increasingly sophisticated tool use.
But there’s a cost. Bipedalism made childbirth dangerous. The reshaped pelvis created a narrower birth canal. Human infants are born earlier in development than other ape infants—their heads need to fit through the canal. This means human babies are helpless for longer, requiring extended parental care.
The hands. Human hands are remarkable instruments. Our thumbs are fully opposable—they can touch each fingertip, enabling precision grip. Our fingers are relatively long and flexible. The muscles and nerves controlling the hand are extraordinarily developed.
Other primates have hands too. Chimps can use tools. But human hands have finer motor control, more sensitivity, greater versatility. We can thread needles, play pianos, perform surgery. These capacities far exceed what’s needed for basic survival—they’re enabling conditions for technology that didn’t exist when the hands evolved.
The vocal tract. Human throats are structured differently from other ape throats. Our larynx sits lower, creating a longer pharynx. This allows us to produce a wider range of sounds—the vowels and consonants that make human speech possible.
The change carries a risk: humans choke on food more easily than other apes because of the modified throat. Evolution made this trade-off anyway. The benefit of speech outweighed the danger of choking.
Other species communicate. None produce the range and precision of human speech sounds. This isn’t just about vocal cords; it’s about the entire vocal apparatus—tongue, lips, palate, breath control—working together with unprecedented refinement.
The eyes. Human eyes have a feature unique among primates: visible whites (sclera). In other apes, the sclera is dark, making it hard to tell where they’re looking. In humans, the white background makes gaze direction obvious.
Why does this matter? Because it enables shared attention. You can tell what I’m looking at; I can tell what you’re looking at. We can coordinate attention without speaking. A mother can direct an infant’s attention with her eyes. A hunter can signal to a partner. This may seem trivial, but it’s the foundation of much social cognition—and other species don’t have it.
10.2 The Brain
The human brain is not the largest in absolute terms—elephants and whales have larger brains. But relative to body size, it’s exceptional.
| Species | Brain-to-body ratio |
|---|---|
| Human | 1:40 |
| Dolphin | 1:80 |
| Chimpanzee | 1:150 |
| Elephant | 1:560 |
More importantly, the human brain is structured differently. The prefrontal cortex—associated with planning, decision-making, and social cognition—is proportionally larger than in other primates. The areas devoted to language are greatly expanded. The connections between regions are denser and more numerous.
But here’s what’s puzzling: the differences are quantitative, not qualitative. Human brains are bigger and more connected, but they’re made of the same stuff as other mammal brains. The same neuron types, the same neurotransmitters, the same basic architecture.
A chimp brain is roughly one-third the size of a human brain. Is a factor of three enough to explain the difference between using sticks to extract termites and building particle accelerators?
Something is missing from this picture.
Energy demands. The brain is metabolically expensive. It constitutes about 2% of body mass but consumes 20% of metabolic energy. Human brains require about 400 calories per day just to run—a significant portion of total energy intake.
Sustaining such an organ requires reliable, high-quality food. This may explain why cooking was transformative: cooked food releases more calories and is easier to digest, enabling the energy surplus needed for large brains.
Development. Human brains develop slowly. At birth, a human brain is about 25% of its adult size; it takes roughly two decades to fully mature. This extended development allows more learning, more neural plasticity, more cultural shaping of brain structure.
But it also requires extended care. Human children are dependent for far longer than other ape children. This necessitates stable social groups, cooperative child-rearing, and the kind of social complexity that characterizes human societies.
Neuroplasticity. Human brains are exceptionally plastic—they’re shaped by experience more than other animal brains. The same genetic blueprint produces a brain that can learn Sumerian or C++, that can navigate Australian deserts or Manhattan streets. The flexibility is extraordinary.
This plasticity is a double-edged sword. It means humans need extensive learning to become competent—a long, vulnerable childhood. But it also means humans can adapt to an enormous range of environments and challenges without genetic change.
10.3 The Gap
Now consider the puzzle.
Chimpanzees share approximately 98.8% of our DNA. Our last common ancestor lived only 6–7 million years ago—a blink in evolutionary time. The biological differences are real but modest.
Yet the outcome differences are astronomical.
| Chimpanzees | Humans |
|---|---|
| Use sticks to extract termites | Built the Large Hadron Collider |
| Communicate with gestures and calls | Created literature, mathematics, music |
| Live in groups of 30–50 | Organize societies of billions |
| Range across hundreds of square kilometers | Have visited the moon |
The proportionality is off. A 1.2% genetic difference doesn’t seem like it should produce a million-fold difference in capability.
Consider other intelligent species:
Dolphins have large brains, complex social structures, sophisticated communication. They’ve existed for tens of millions of years—far longer than humans. They’ve built nothing.
Elephants have large brains, excellent memories, complex social bonds, apparent self-awareness. They’ve existed for millions of years. They’ve built nothing.
Corvids—crows, ravens, jays—have remarkable problem-solving abilities. They use tools, plan for the future, remember faces, hold grudges. They’ve existed for tens of millions of years. They’ve built nothing.
Octopuses have complex brains, can solve puzzles, learn through observation. They’ve existed for hundreds of millions of years. They’ve built nothing.
The pattern is clear: intelligence, on its own, doesn’t produce civilization. Something else is needed. Something that other intelligent species lack.
What is it?
10.4 Necessary, Not Sufficient
Here’s the honest assessment of human biology:
Our bodies and brains are necessary conditions for civilization. Without bipedalism, our hands wouldn’t be free for tool use. Without the vocal tract, we couldn’t have language. Without large brains, we couldn’t handle the cognitive demands of complex culture.
But these features are not sufficient. Other species have hands; other species communicate; other species have large brains relative to their needs. The biological hardware enables civilization but doesn’t guarantee it.
The standard account goes something like this:
- Bipedalism freed hands → tool use became possible
- Tool use created selection pressure for larger brains
- Larger brains enabled more sophisticated tools and social cooperation
- Social cooperation favored communication → language evolved
- Language enabled sharing of knowledge across generations
- Cumulative knowledge eventually produced agriculture, cities, science
Each step is plausible. Together, they form a coherent narrative. The narrative is probably broadly correct.
But it leaves questions unanswered.
Why this lineage? Other primates faced similar pressures. Why didn’t multiple lineages develop civilization in parallel?
Why this timing? The biological prerequisites were in place for hundreds of thousands of years before civilization emerged. What changed 12,000 years ago that hadn’t changed before?
Why this speed? Once civilization started, it accelerated exponentially. The biological hardware didn’t change in the last 10,000 years. What’s driving the acceleration?
The biological story explains the foundation. It doesn’t explain the explosion.
For that, we need to look at something else—something that happened not in our genes but in our cultures. The biological evolution gave us the capacity. Something else gave us the trajectory.
That something else is the subject of the next chapter.
Coda: The Bridge
Think of human biology as a bridge.
On one side: the animal world, the world of instinct and adaptation, the world where creatures do what evolution shaped them to do and no more.
On the other side: the world of culture, technology, cumulative knowledge, exponential growth.
The bridge is our bodies and brains—the biological prerequisites that make it possible to cross. But crossing the bridge requires something more than having the bridge available.
Most intelligent species never cross. They have pieces of the bridge—tool use, communication, social learning—but not the complete span. They remain on the animal side.
Humans crossed. At some point in our history—perhaps 70,000 years ago, perhaps earlier, perhaps in stages—we crossed from one side to the other. We entered a new mode of existence, one where each generation could build on the previous, where knowledge could accumulate, where the curve could begin its exponential rise.
The question is: What was the crossing? What did we do—or what happened to us—that other species haven’t done and hasn’t happened to them?
The biological prerequisites are the bridge. The crossing is something else.
Let’s look at the crossing.