Seven million years ago our ancestors were chimpanzees living in a forest in Africa. Then a drought caused a food shortage, and some of them walked into the grassland looking for food. That change in their environment set the evolution of human intelligence in motion.
ACT I
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7 million years ago, in southeastern Africa, there was a forest, where chimpanzees lived. They weren’t chimpanzees as we know them today. They were the ancestors of the chimpanzees of today. But I’m still going to call them chimpanzees.
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Chimpanzees, and all other primates, have two important traits. They climb in trees and they live in groups.
Climbing in trees means their front legs and feet have evolved into arms and hands that are good for grabbing and holding onto branches. Since their hands are so good at grabbing and holding things, chimpanzees also pick up and use things like sticks, rocks, leaves, and grass. They use rocks to smash open nuts and gourds, and sticks to reach into places they can’t reach with their hands.
Living in groups means they have more highly developed social instincts than mammals who don’t live in groups. They cooperate for their mutual interests, like protecting themselves from predators. But they still compete for their individual interests, like mating.
One thing that means is that primates pay attention to what each other are doing more than mammals who don’t live in groups do. Another is that they communicate more information with each other with things like sounds and body language.
ACT II
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At the edge of the forest the trees thinned out. Beyond that was grassland.
Then a drought caused a food shortage in the forest. The chimpanzees got hungry. Some of them walked out into the grassland looking for food.
They found food there. But they were at a disadvantage to the other animals that lived there.
The animals that lived on the plains walked on four feet all the time. That let them run fast.
Primates walk on all fours when they’re on the ground. But since their arms and hands have evolved so much for climbing in trees they can’t run as fast as animals that walk on all fours all the time. Out in the grassland, where there weren’t any trees to climb, the chimpanzees lost their advantage.
But something new started happening. Chimpanzees can stand on their hind legs. Standing on their hind legs let them see over the top of the grass.
That let them see the lions and other predators approaching. That helped them escape, because instead of running faster, they ran sooner.
Some chimpanzees stood on their hind legs more often than the others. That let them see the predators coming more often. That gave them a higher survival rate.
Eventually all the chimpanzees stood on their hind legs all the time, because all the rest of them got eaten.
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These chimpanzees could still use their hands for picking up and using objects.
We can call those tools, or inventions. Both of those mean anything external to your body that you decide to use for a purpose.
If you use a rock to hit something harder than you can hit it with your hand, or a stick to poke something you don’t want to touch with your hand, you’ve invented a tool, even though you just picked it up off the ground.
Now that the chimpanzees on the plains weren’t using their hands for climbing or walking anymore, they got better at using tools. Some of the most obvious things they could do was to use sticks for clubs and spears and throw rocks, which made them a lot better at protecting themselves from predators.
There are two parts to using tools. There’s the anatomy of your hand for holding and using the tools. There’s also your brainpower for thinking of things to use tools for.
That means imagining ways to use tools and remembering ways you’ve seen other people use tools. So replication, variation, and selection started favoring the chimpanzees with the best hands for using tools and the most intelligence for thinking of ways to use tools.
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There are two parts to selection. Environmental selection is selection by survival, where the members of the species who are the best fit to the environment are the ones who survive, and the rest die out.
Sexual selection is selection by reproduction. The members of the species that have the most offspring that grow up to have more offspring pass on the most of their genes.
The two can feed into each other. In the evolution of human intelligence they fed into each other a lot.
Now that the chimpanzees on the plains weren’t using their hands for walking or climbing anymore, they evolved to be better at using tools.
Among animals, the members of a species who are the best at surviving are the healthiest ones. So animals who are attracted to healthy mates combine their genes with them and have healthy children.
Just like every other trait that’s a product of evolution. Animals have genes for being attracted to healthy mates, because the ones who had genes for being attracted to unhealthy mates had unhealthy children who died out. So when a new characteristic, like intelligence, helps the members of a species survive, it makes the ones with the most of it healthier than other members of the species, and soon that makes them some of the most attractive mates.
The chimpanzees who could use their hands and their brains to use tools the best were able to do the most things for themselves. Tools helped them fight off predators the most, and also helped them get the most to eat, win fights against other chimpanzees, and intimidate or show off to other chimpanzees.
All those things that helped them survive made them some of the healthiest members of the species. Now when all the chimps tried to mate with the healthiest members of the opposite sex, the ones who were the best at using tools ended up having the most children.
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The chimpanzees’ brains evolving to think of ways to use their hands to use tools set the evolution of their intelligence on a path no other species could follow. Animals who don’t use tools have to use their bodies to do everything they need to do in life.
Pick any animal, from a fish to a bird to a frog to a hippopotamus, and make a list of all the things it can do with each of its body parts. Each of those lists will be pretty short. Their brains evolved to think about all that stuff.
Then try to make a list of all the things people can do with our hands. Our brains evolved to think about all that stuff.
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In one sense, tools are additions to our bodies. They let us do things we can’t do with our bodies.
In another sense, they’re extensions of our bodies. They increase our abilities to do things we can do with our bodies. Any physical action you can imagine taking with a tool begins with a physical action you can imagine taking with your body.
You can hit an animal with your hand, and you can hit it harder with a club. Or you can throw a rock and hit it from a distance.
You can bite pieces off of a dead animal with your teeth. You can cut up a dead animal more easily with a sharp rock. First our ancestors did that with sharp rocks they found. Eventually some of them figured out how to chip sharp edges onto rocks.
Essentially, these chimpanzees’ hands evolved into body parts for making new body parts. That let our ancestors’s brains evolve to think about more things they could do without needing to evolve any more body parts. That let their intelligence evolve faster and further than any other species.
ACT III
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These new levels of brainpower created new selection pressures within their groups. Now that new levels of tool-using intelligence were giving the chimpanzees new advantages, and giving some of them more advantages than others, two other forms of intelligence started giving them advantages also.
One was intelligence for thinking about what other chimpanzees were thinking about. All animal species have instincts for interacting with other members of the species. Because at the very least they need to interact with other members in order to mate and to compete for mates.
Primates live in groups, where they cooperate for their mutual interests and compete for their individual interests. A group of chimpanzees can work together to fight off predators. But each female can only get pregnant by one male at a time. Or if a group of chimpanzees finds some food but it isn’t enough for all of them to eat as much as they want, how do they divide it up?
Chimpanzee groups today are full of political and romantic intrigue, as chimps try to outsmart each other on some things while cooperating on other things.
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Now that using tools was making individuals more powerful, figuring out what the others were doing, what they were trying to do, and what they wanted became much more important.
This led to the evolution of self awareness. Again, different species have different levels of self awareness. That’s affected by how much the members of the species interact with each other. The more we think about what other members of our species are thinking, the more we think about how it relates to us.
Now that tools were making the members of the group more powerful, and figuring out what each other were doing was more important, individuals thinking about themselves became more important.
Self awareness and group awareness helped chimpanzees survive by outsmarting the others or by finding more advantageous ways to cooperate with them. That made the ones who were best at those the healthiest. Once again, when all the chimps tried to mate with the healthiest chimps, the ones who were the most self aware had the most children.
Eventually our ancestors evolved so much self awareness they could imagine different paths their lives could take, up to their old age and death, and imagine who their grandchildren and great-grandchildren might be and what could happen to them.
ACT IV
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Another part of the chimpanzees’ social instincts was communication.
All mammals make sounds with their mouths to communicate. If you own a dog, you might’ve noticed that it makes different sounds when it’s hungry, when it wants to go out, or when it hears someone approaching. Chimpanzees today are better than any other species (besides us) at communicating with each other.
In a group of chimpanzees who are using tools, and who are thinking about each other and themselves, another way to keep track of what’s happening in the group and to find more and better uses for tools is to pass information around.
The simplest words are nouns, because they refer to objects that two individuals can look at. If someone points at a rock and makes a sound with their mouth, and points at a stick and makes a different sound with their mouth, and when you make one of those sounds with your mouth the other person points to the thing you’re talking about, the two of you are communicating.
Communication helped chimpanzees survive by helping them gather more information to use in their decisions. Once again, the ones who were the best at it were among the healthiest members of the species. So once again, when all the chimps tried to mate with the healthiest chimps, the ones who were best at using words had the most children.
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The evolution of our intelligence started out slow.
It took about 3 million years for our ancestors to start walking on two feet. It took another million and a half years for them to start intentionally chipping stones. It took about another million years for them to start using fire.
But as you can see, the evolution of their intelligence was speeding up. These landmark events keep getting closer together. Our ancestors were evolving three forms of intelligence at the same time, and every generation the most intelligent ones had the most children.
Then about 80,000 years ago the evolution of intelligence really took off. We can infer that the evolution of tool use, self awareness, and language came together to create a new level of abstract thinking. That’s when our ancestors’ campsites start showing remnants of much more complicated creations. Like multi piece tools, specialized tools, sewn clothing, and artwork that’s comparable to artwork today.
At that time our ancestors started making much bigger decisions in the things they made. That means they were using a lot more information.
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The things people started making during this intelligence revolution make it look as though they reached a point of being able to get a lot of information from each other, by asking each other why? and how? and what if? and talk about patterns of cause and effect using some abstract terms.
They had to be able to think about cause and effect in abstract terms already, to be able to remember what they’d seen and done with tools already, and to be able to imagine what could happen. If they were already using nouns for objects and they were thinking about abstract ideas, the next easiest ideas to communicate with each other would be verbs, adjectives, and pronouns. Then prepositions, adverbs, conjunctions, and nouns that represent ideas.
The first people to talk about abstract ideas probably couldn’t think about all the things we think about. The evolution of language probably contributed to some of the evolution of our abstract intelligence. Once people began putting some abstract ideas into words, that probably helped them think of other ideas that were even more abstract.
On the other hand, we can see that much of our ancestors’ abstract thinking was already there. Around the time our ancestors started using their abstract thinking to make tools by connecting pieces together, they also invented art and religion.
Around the time they figured out how to connect stone axe heads to wooden handles and sew clothing from animal hides with bone needles and leather cords, they also figured out how to make flutes out of bones that let them play different notes by covering different holes, paint pictures on cave walls that show scenes, and they started burying their dead with valuable possessions, as if the dead people were taking those things with them into the afterlife.
ACT V
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One good introduction to this part of the story is a book called Human Natures, by Paul Ehrlich.
Another is called The Third Chimpanzee, by Jared Diamond.
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This intelligence revolution took about 30,000 years. That brings us up to 50,000 years ago.
At that point our ancestors were behaviorally modern humans, meaning, people like us.
At that point they were making all the basic things that stone age people of today and of recent history made. And the only things that separate us from stone age people today are technology, social developments, and other inventions and ideas.
There are stone age people living in parts of South America, Africa, Asia, and the Pacific Islands today, and some of their children and grandchildren grow up to be computer engineers.
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However it happened exactly, the intelligence revolution involved many different inventions for many different purposes. It shows purposeful creativity combined with abstract thinking. Those show a big increase in information processing, and that points to a big increase in communication.
That’s where human psychology begins.