Chapter 11
THE RATCHET
Cumulative culture—the ability to build on what came before—is the key.
11.1 The Difference
Here is the difference between humans and every other species on Earth:
A chimpanzee learns to crack nuts with a stone. She teaches her offspring. The offspring teach their offspring. Ten thousand generations pass. The chimps are still cracking nuts with stones, in essentially the same way, with essentially the same skill level.
A human learns to crack nuts with a stone. He teaches his children. One child experiments—maybe a different angle, a different stone, a slight innovation. The innovation is passed on. Another generation, another small improvement. Ten thousand generations pass. The descendants have agriculture, metallurgy, writing, cities, computers, spacecraft.
The difference is not that humans learn. Other animals learn.
The difference is not that humans teach. Other animals teach.
The difference is not that humans imitate. Other animals imitate.
The difference is that human knowledge accumulates. Each generation can start where the previous generation ended. Improvements are preserved and built upon. The ratchet clicks forward and doesn’t slip back.
This is cumulative culture, and it appears to be unique to humans.
11.2 The Mechanism
How does cumulative culture work? What makes it possible?
High-fidelity transmission. For knowledge to accumulate, it must be transmitted accurately. If each generation loses 20% of what the previous generation knew, the ratchet slips—knowledge degrades rather than builds.
Humans transmit with remarkable fidelity. A master potter teaches an apprentice; the apprentice can reproduce the technique precisely. A musician passes on a melody; the melody survives unchanged for centuries. A mathematician proves a theorem; the proof can be reconstructed by anyone who reads it.
Other animals transmit culture too, but with lower fidelity. Birdsong dialects drift over generations. Chimp tool techniques vary between populations and decay over time. The copies are lossy.
Human copies can be lossless—or close enough.
Intentional teaching. Most animal learning happens through individual trial and error, or through observation without explicit instruction. A young chimp watches its mother crack nuts and tries to imitate. The mother doesn’t adjust her behavior to help the young chimp learn.
Humans actively teach. We slow down, demonstrate, correct, explain. We design our teaching to transfer information efficiently. We create curricula, exercises, feedback loops.
This intentional pedagogy dramatically increases the fidelity and speed of transmission. A skill that might take years to acquire through observation alone can be taught in weeks with explicit instruction.
Language. Here is where language becomes crucial—not just for communication but for cultural transmission.
Language allows us to transmit information that cannot be observed. I can tell you about things that happened in the past, things that might happen in the future, things that exist in places you’ve never been. I can describe abstract concepts, counterfactual scenarios, precise sequences of actions.
Without language, transmission is limited to what can be demonstrated and observed. With language, transmission can include anything that can be put into words.
Language also allows error correction. If you’re learning a skill and doing it wrong, I can explain what’s wrong. I can describe the correct technique even when you’re not currently performing it. I can give you principles, rules, heuristics that guide future attempts.
External memory. Language transmits across space and time—but only when speakers and listeners overlap. The knowledge dies when the last knower dies.
Writing changed this. Suddenly, knowledge could be stored outside any human mind. A Sumerian scribe could record an observation, and a Babylonian scholar a thousand years later could read it. The transmission no longer required personal contact.
Writing created a new kind of memory—external, persistent, expandable. Libraries became repositories of accumulated knowledge. Each generation could access not just what their parents knew but what countless previous generations had recorded.
The ratchet gained a new mechanism. It could click forward even when individual humans forgot, even when entire communities perished. The written record survived.
Printing, then digital storage. Each technology of external memory accelerated the ratchet further. Printing made texts cheaper, more numerous, more widely distributed. Digital storage made information infinitely copyable, instantly searchable, globally accessible.
The ratchet clicks faster now than ever before. An insight discovered in Tokyo can be read in Toronto within seconds. A paper published today joins a corpus of billions of documents, all searchable, all cross-referenced, all available to anyone with an internet connection.
11.3 Why Humans Only?
If cumulative culture is the key, why do only humans have it?
The honest answer: we don’t fully know. But we can identify factors that seem necessary, and we can observe that only humans have all of them together.
Factor 1: Teaching. True teaching—adjusting behavior to help another learn—is rare outside humans. Some species show hints of it: meerkats bring disabled prey to their young, allowing practice with reduced risk. But nothing approaches human pedagogy.
Teaching requires something cognitively demanding: the ability to model another mind, to recognize what the other knows and doesn’t know, to design actions that bridge the gap. This “theory of mind” is highly developed in humans and limited in other species.
Factor 2: Imitation fidelity. Humans imitate with extraordinary precision. Show a human a complex action sequence, and they can reproduce it step by step. Show a chimp, and they’ll get the gist but miss the details.
The difference may seem subtle, but it’s crucial for cumulative culture. If each transmission loses information, the ratchet slips. High-fidelity imitation keeps the ratchet locked.
Factor 3: Language. No other species has anything like human language—the open-ended, combinatorial, endlessly generative system that allows us to express any thought we can conceive.
Other animals communicate. Bees signal distance and direction to flowers. Vervet monkeys have different alarm calls for different predators. But these systems are closed—limited sets of signals for limited purposes. They cannot express novel ideas, abstract concepts, hypothetical scenarios.
Human language can express anything. This makes it possible to transmit anything—including innovations too subtle to demonstrate, too abstract to observe, too complex to figure out independently.
Factor 4: Motivation. Humans are motivated to share knowledge in ways other species aren’t. We teach voluntarily, even when it costs us time and energy. We feel satisfaction when others learn from us. We build institutions—schools, apprenticeships, universities—dedicated to transmission.
This may be connected to our social nature. Humans depend on their groups; knowledge that helps the group helps the individual indirectly. There may also be status incentives: being a teacher confers respect.
Whatever the reasons, humans actively want to pass on what they know. This motivation drives the ratchet forward.
The combination. No single factor explains human uniqueness. Other species have some of these traits in limited form. What humans have is the complete package: high-fidelity imitation, intentional teaching, open-ended language, motivation to share, and technologies (writing, printing, digital) that extend transmission across time and space.
The package enables cumulative culture. Cumulative culture enables the exponential curve. The curve produces civilization.
11.4 The Ratchet Effect
Let’s be precise about what the ratchet does.
Imagine two populations, each starting with knowledge level K.
Population A (no ratchet): Each generation learns skills afresh. Some individuals figure out improvements, but improvements don’t reliably transmit. Average knowledge fluctuates around K, sometimes higher, sometimes lower, but with no consistent trend.
Population B (with ratchet): Each generation starts where the previous ended. Improvements, once discovered, are preserved and transmitted. Average knowledge starts at K, then K+1, then K+2, then K+3… The curve rises.
Now add time. After a hundred generations:
- Population A: still around K
- Population B: at K+100 (at minimum; probably much higher, since each increment enables further increments)
After a thousand generations:
- Population A: still around K
- Population B: at K+something enormous, limited only by what’s possible
This is the ratchet effect. It’s not that humans are smarter than chimps at each generation. It’s that each human generation starts further along than the last. The advantages compound.
An analogy. Imagine two people trying to climb a mountain. One (the chimp) climbs during the day, but each night slides back to the bottom. The other (the human) climbs during the day and stays where they reached overnight. Who gets to the summit?
It doesn’t matter if the first person is a better climber. The second person will win eventually, because progress accumulates.
Human civilization is the accumulated progress of thousands of generations, each standing on the shoulders of those before. We’re not inherently smarter than our ancestors. We just have more to work with.
The compounding. The ratchet doesn’t just add; it multiplies.
Each new piece of knowledge enables discoveries that couldn’t have been made without it. Metallurgy enables better tools. Better tools enable agriculture. Agriculture enables surplus. Surplus enables specialization. Specialization enables cities. Cities enable writing. Writing enables cumulative culture to accelerate further.
The curve doesn’t rise linearly. It rises exponentially—or faster—because each increment increases the rate of future increments.
This is what we see in human history. The explosion of the last 10,000 years, the further explosion of the last 500 years, the still further explosion of the last 50 years. Each era is faster than the last because each era has more accumulated knowledge to build on.
Coda: The Power and the Fragility
The ratchet is powerful. It explains how a species with modest cognitive advantages over its relatives could produce achievements incomparably beyond anything else in the history of life on Earth.
But the ratchet is also fragile.
It depends on transmission. If transmission fails—if knowledge isn’t passed on—the ratchet slips. We’ve seen this happen. The Greek Dark Age. The fall of Rome. The Bronze Age collapse. Each involved loss of knowledge, loss of literacy, loss of accumulated culture.
The losses are not always recovered. Some ancient techniques are lost permanently. Some texts exist only in fragments, or not at all. The Library of Alexandria burned; we don’t know what was inside.
The ratchet can slip backward. It has slipped backward. Civilization is not inevitable; it’s contingent, dependent on institutions and circumstances that maintain transmission.
This should give us pause. The exponential curve we’re riding is not a law of nature. It’s an achievement—a fragile, ongoing achievement that requires constant maintenance.
The Sumerians built the first libraries. The knowledge they accumulated made us possible. We owe them—and every generation since—a debt that can only be repaid by continuing the transmission, keeping the ratchet from slipping, passing on what we’ve received so that those who come after can build on it.
The ratchet clicks forward. Our job is to keep it clicking.