Standard advice for how to read a book goes something like this:
- First, skim the entire book, try to get the big picture.
- Next, read the book quickly, getting a medium-level view.
- Finally, actually read the entire book carefully.
Sensible enough. The basic theory here is that we need a conceptual framework in which to organize information. This is hard to build if we just consume detail after detail in a linear fashion.
But if that’s true, then why are books always written as detail after detail in a linear fashion? Shouldn’t the book explicitly provide the same content with different levels of detail?
Reading Sapiens by Yuval Harari, I decided to try creating these other levels. This post is my summary of part one of that book. And also a summary of that summary.
Sapiens, Part 1. Summary of Summary
Many different species of humans have existed since 2.5mya. For most of that time, humans were not dominant over other species. The key differentiators were giant brains, walking on two legs, complex social structures, tools, and cooking.
Sapiens evolved in East Africa 150kya, In the cognitive revolution 70kya, Sapiens evolved language. This made it possible to describe complex ideas and to gossip. Gossip made it possible to cooperate in groups of up to 150. Invented myths like religions made it possible to cooperate in even larger groups. These abilities to cooperate made Sapiens more powerful than animals or other humans.
After the cognitive revolution, Sapiens quickly overran Africa, Asia, and Europe, eliminating all other humans. Then, after inventing boats, clothing and snowshoes, Sapiens reached landmasses no other humans had ever seen. They settled Australia 45kya and America 14kya. Wherever they went, most large animals soon went extinct. This happened because those animals had not evolved to avoid humans, and couldn’t cope with the large-scale fires Sapiens set.
We only have a superficial picture of forager life after the cognitive revolution. Foragers lived in intimate, mostly nomadic bands of a few dozen to a few hundred. They needed to master a huge number of skills. Foragers were extremely fit due to varied diets and constant exercise. This era is still our “home” with the diet, exercise, and social structure we evolved for. It was common to die suddenly from childbirth, accidents, or violence.
Sapiens, Part 1. Summary
Here we are, with our plumbing and satellites and quantum mechanics. How did we get here, and why are we like we are?
Big picture, our history is as follows:
- 13,500,000,000 years ago – The universe comes into being.
- 3,800,000,000 years ago – Molecules form on Earth to create life.
- 2,500,000 years ago – Humans evolve
- 150,000 years ago – Homo sapiens evolve
- 70,000 years ago – The cognitive revolution.
- 12,000 years ago – The agricultural revolution.
- 500 years ago – The scientific revolution.
The first part of Sapiens tells the story of how humans evolved from other animals, how we Sapiens evolved from other humans, and how we took over the planet.
There have been many types of humans (species of the genus homo) for a long time. Humans first evolved in East Africa from other apes 2.5 mya and settled settled Europe, North Africa, and Asia by 2 mya.
Different populations evolved in different areas, adapted to local conditions. In Europe, Homo neanderthalis were bulkier and adapted to the cold. In East Asia, Homo erectus were the first capable of using fire and hunting in groups. These survived for 2 million years. On Flores island in Indonesia, Homo floriensis weighed at most 25kg. In 2010 in a new species, Homo denisova was discovered in a cave in Siberia. At the same time East Africa produced more species: Homo rudolfensis, Homo ergaster, eventually Homo sapiens. Critically, until 10kya, there were many different human species, all around at the same time.
These archaic humans weren’t particularly dominant. They lived in constant fear of predators. Still, there were two major differences to other animals.
First, humans have massive brains. They are only 2-3% of mass, but consume 25% of energy, compared to around 8% for other apes. (Incidentally, neanderthals had bigger brains than Sapiens.) Evolution reduced the size of muscles to “pay” for this energy expenditure.
The value of our gigantic brains today seems obvious. But 2mya the most salient outcomes were simple tools like flint knives and pointy sticks. Was this really worth it? Or were there more subtle benefits? This apparently remains a mystery.
Second, humans stand upright. This allows us to see further and frees arms for stuff like throwing rocks. We developed extra nerves and muscles to allows us to perform intricate tasks. Humans always had simple tools.
Standing has downsides. We arguably haven’t fully adapted to it, hence backaches and stiff necks. Further, standing requires narrower hips, which means extra deaths in childbirth. This selected for women who gave birth earlier. Human babies became undeveloped and helpless. This then contributed to social abilities, since lone mothers couldn’t survive.
Cooking and controlling fire is a first major gap between humans and other species. Various human species mastered fire by 300kya. This provided defense, light, and heat. But cooking was the biggest benefit. It killed microorganisms, allowed a larger variety of foods, and greatly reduced time spent eating. Evolution could spend less energy on teeth and intestines.
These archaic humans were not at the top of the food chain. Yes, they had large brains, tools, and social structures. But they were weak, and constantly afraid of predators. They survived off of plants, insects, small animals. The specialized in eating bone marrow, left over after other animals had killed something and literally picked the bones clean. Only 400kya they started to hunt large animals.
Not until Sapiens did humans climb to the top of the food chain. Harari gives the following poetic and somewhat baffling remark:
Most top predators of the planet are majestic creatures. Millions of years of dominion have filled them with self-confidence. Sapiens by contrast is more like a banana republic dictator. Having so recently been one of the underdogs of the savannah, we are full of fears and anxieties over our position, which makes us doubly cruel and dangerous. Many historical calamities, from deadly wars to ecological catastrophes, have resulted from this over-hasty jump.”
By 150kya Homo sapiens evolved in East Africa. These looked just like modern people, but weren’t cognitively the same. They moved out of East Africa 70kya and quickly took over all Eurasia. (Africa and Asia 60kya, Europe and Australia 45kya, and America 15kya). Traditionally, it was debated if they interbred or replaced the other humans already in those places. In 2010 scientists collected enough neanderthal DNA to compare to modern humans. Europeans probably have 1-4% neanderthal DNA. Aboriginal Australians might have 6% Homo denisovan DNA! So these weren’t quite distinct species.
It’s unclear exactly how the process of Sapiens displacing other humans went. There could have been conflict and genocide. Or, perhaps the other species slowly retreated and were out-bred. Regardless, almost all other humans were gone by 30kya. The drawf-like humans in Flores finally vanished when Sapiens arrived 12kya.
What happened to Sapiens 70kya that caused them to take over the world? The answer is the cognitive revolution: They evolved language and culture.
Before the cognitive revolution, Sapiens had left East Africa, but were driven back by Neanderthals. Then, between 70k and 30kya they invented boats, oil lamps, bows and arrows, needles and art and then took over Europe, East Asia, and Australia.
This all happened because of language. Why did language happen to Sapiens, rather than Neanderthals, or some other species? It seems to be simply because of accidental mutations.
Are Sapien language capabilities really unique? Yes. Other animals can communicate by making sounds. Indeed, some birds are much better at making sounds than you. However, they have a finite vocabulary, things like “hawk!” or “enemy monkeys”. Sapiens can express an infinite number of sentences with distinct meaning.
There are two theories for why language evolved. The first is that it was for compound propositions like “There is a beehive behind the tall bush a five-minute walk down the river”. The second is that language evolved for gossip. Since we are so social, it’s crucial to keep track of what’s going on with all the other relationships in your band. You can’t observe it yourself, so talk to others. Still today much — or even most? — human communication is some form of gossip.
Gossip is powerful. However, the number of relationships in a group is the square of the number of people in it. At some point, our ability to keep track of all the relationships breaks down. This seems to happen around 150 individuals. Still today we have many organizations (family businesses, military companies) that work well up to this size with minimal internal organization. But beyond that, gossip doesn’t seem to suffice.
After language came fiction: Myths, gods, and religions. These really are unique to humans — try getting a monkey to trade you a banana for some virgins in the afterlife. At first, this seems strange. Isn’t it harmful to believe in false things? Why would evolution favor that? In fact, fictions are tremendously useful. They allow cooperation at a larger scale than gossip. For a very large groups to cooperate, there needs to be an agreed set of rules. Kings have no true divine rights. But if we believe they do, then it is possible for countries to exist. Even if kings are greedy, they want to avoid bands fighting each other, which is a huge win. So myths can reduce internal conflict. Similarly, large international corporations don’t “really” exist. But because we believe they do, thousands of people can work together to accomplish things.
Mythical beliefs allow Sapiens to adapt rapidly, bypassing genetic evolution. When convenient we are eerily quick to discard divine kings and adopt human rights. It’s not important if mythical beliefs are *true*. What matters is the behaviors they instill in us.
A Neanderthal would probably beat a Sapien in a 1-on-1 fight. But in a group of hundreds, Sapiens could cooperate much more effectively. Sapiens traded over long distances. Neanderthals never did. Sapiens had hunting techniques involving dozens– for example, surround an entire heard and chase them into a gorge. Neanderthals hunted in at most small groups.
To summarize, what new abilities did language give us?
|New Ability||What Became Possible|
|Transmit larger quantities of information about the surrounding world.||Plan and carry out complex actions like hunting bison.|
|Transmit larger quantities of information about social relationships.||Cohesive groups of up to around 150 people possible.|
|Transmit information about myths, like spirits, nations, companies, human rights.||Cooperation of groups even larger than 150 people. Also enabled evolution of social behavior, at a rate much faster than genetic evolution.|
Here’s a cute way of putting it: Imagine an equal number of chimps will fight an equal number of Sapiens. Neither has any weapons or tools. Suppose the fight is:
- 3 vs. 3: This fight would probably be a close thing.
- 15 vs. 15: The Sapiens would be favored. They could make a plan and communicate on the fly.
- 1000 vs 1000: The Sapiens would be insanely favored. They could invent tactics and movement patterns the chimps would be helpless to counter.
The cognitive revolution is where “biology” becomes “history”. We cannot understand the French revolution in terms of genes and hormones. While biology sets the parameters, the main show is the social evolution of behavior. If you want to understand what happens, you must follow the dynamics of the invented fictions.
What happened after the cognitive revolution? Sapiens quickly spread over Africa, Europe and Asia, displacing all other humans. Then they found previously untouched landmasses, Australia and America.
Sapiens settled Australia 45kya. This is an accomplishment, as it was necessary to repeatedly cross channels, some hundreds of km wide, and then survive in a different ecosystem at the end. Probably Sapiens in Indonesia developed ocean-going boats for fishing and trading, but there’s no proof. In principle, people might have swam to Australia? This is unlikely. No other mammal ever crossed from Asia to Australa.
Then, everything died. Before Sapiens, there were giant birds, lizards that looked like dragons, and kangaroos and wombats that weighed more than 2 tons. Within a few thousand years, 23/24 Australian animals that weight 50kg or more were extinct. There were climactic changes around the same time, but these are probably not the main cause. Ocean animals were fine.
How did all these animals go extinct? There are three possibilities:
1. Maybe the animals were very easy to kill because they didn’t evolve alongside archaic humans for millions of years like the animals in Africa, Europe and Asia did. Giant wombats probably didn’t need to fear any other animals the size of Sapiens. Genetic evolution was too slow to save them.
2. Maybe humans transformed the environment using fire agriculture. It was common to burn forests to create grasslands– much better for hunting. Eucalyptus trees are robust to fire. These were rare before Sapiens came, but common after.
3. Maybe the animals were very unlucky to hit climate changes and Sapiens at the same time. Perhaps they could have adapted to one or the other, but not both at the same time.
Sapiens got to America around 16kya. This was even more impressive. Yes, they walked over from Asia because sea levels were low. But they had to adapt to the extreme conditions on Northern Siberia, where no other humans ever survived. They had to invent snowshoes, clothing, new weapons and hunting techniques. They couldn’t settle south of Alaska until around 14kya when global warming melted glaciers. By around 12kya, Sapiens had settled the southern tip of Argentina. This is incredibly rapid — moving south, they had to adapt over and over again to different climates.
Again, after Sapiens got to America, most of the large animals died. There were originally Mammoths, mastatons, bear-sized rodents, giant lions and cats, herds of horses and camels, and 6m tell 8 ton ground sloths. Overall, the Americas lost 84/107 large mammals. Many of these had lived for tens of millions of years, but were extinct within 2k years of Sapiens’ arrival. Some survived on Carribean islands for a while, but then disappeared after settled those islands.
Madacascar was only reach 1.5kya, Same story.
There are tons of islands throughout the world reached at various times. Same story.
What was life like after the cognitive revolution?
Why do must of us eat too much high-calorie food? It’s generally agreed that’s because we had little access to sweet food in our evolutionary history. You should gorge of ripe fruit if you almost never find it.
It’s hard to learn much about forager life. For example, were our forager ancestors monogamous or communal? Was there private property? Were there nuclear families? Was there philosophy or music?
Why is it so hard to know much? One major difficulty is that artifacts from wood, bamboo, and leather rarely survive. We mistakenly think of the “stone” age. In any case, foragers moved frequently, carrying everything on their backs, so they surely had few possessions anyway.
Another strategy is to study modern foragers. However, this is misleading. First, they are all influenced by neighboring societies. Second, the surviving forager cultures are mainly in areas very poor for agriculture, such as harsh climates. This would greatly mislead as to, say, population density. Third different forager societies are different from one another. Aboriginal australian clans had hundreds of different languages, religions, customs.
What do we actually know?
Animals. The dog was domesticated by 15kya, and perhaps much earlier. Dogs were used for fighting, hunting, and as an alarm system. Dogs probably evolved “accidentally” since those that best met human needs and/or manipulated humans got extra care and food. There were no other domesticated animals.
Society. People lived in intimate bands of a few dozen to a few hundred. There was no privacy or loneliness. There was some contact between different bands, but it was minimal. Most never saw someone outside their band for months on end. There was only trade in “prestige” items like pigments, not in things like fruit or meat.
Movement. Bands roamed back and forth over the same territory of dozens or hundeds of square kilometers. They occasionally explored new lands, due perhaps to conflict, demographic pressure, or the environment. If a band split every 40 years and moved 100km, you’d get from East Africe to China in 10k years, roughly what happened. Rarely, with great food sources, you’d have seasonal or even permanent camps.In particular, there were fishing villages.
Minds. A huge amount of knowledge was needed: What you can eat, what is poisonous, what is a cure, the progress of seasons, how to deal with animals, how to deal with weather, how to make weapons, traps, or clothes. Sapiens mastered techniques for drying, smoking, freezing food. Everyone needed to know basically all of this, whereas today we can hyper-specialize. There is some evidence that our brains have *shrunk* since the age of foraging.
Bodies. The forager diet provided ideal nutrition and exercise. This, after all, is what we adapted for. The diet was highly varied, which provided all nutrients. This was helpful when one source failed. People had incredible physical fitness due to constant exercise. Life expectancy was 30-40 years, though some made it to their 80s. There were few infectious diseases. Most of these came from domesticated animals and only emerged after agriculture. However, there was high child mortality. Any random accident could kill you. It was common to abandon or even kill the old or disabled, or unwanted babies.
Violence. It’s hard to estimate how violent this time was. We can do things like study skeletons and see how many clearly died due to violence. This has been done in different places, giving estimates of 0.25%, 4.5% or 40% ! (This misses soft-tissue damage, so is surely an under-estimate.) So violence was probably very common in some places, and less common in others.
Spirituality. Most believed in various types of animism, that everything is alive and has feelings, including things like rocks. But we don’t know much. (Incidentally, are you familiar with Panpsychism?)
This is the age we evolved for. It provided the diet, exercise, and social structure that is still “home” for us. But you could die at any time from violence or a random accident. We don’t know a tremendous amount about how societies worked, or how common violence was.
Then, we started farming and pretty much everything got worse.