A Brief History of Intelligence: Evolution, AI, and the Five Breakthroughs That Made Our Brains

by Max Solomon Bennett

Even hunter-gatherer societies in Australia and Africa who at the point they were “discovered” had had no contact with any other groups of humans for over fifty thousand years, still spoke their own languages that were equally complex as those of other humans. This is irrefutable evidence that the shared ancestor of humans spoke their own languages, with their own declarative labels and grammars.

Kanzi successfully completed these tasks over 70 percent of the time, outperforming the two-year-old human child.

These apes never surpass the abilities of a young human child. So, language seems unique to humans on two counts. First, we have a natural tendency to construct it and use it, which other animals do not. Second, we have a capacity for language that far surpasses that of any other animal, even if some basic semblance of symbols and grammar is possible in other apes.

Concepts, ideas, and thoughts, just like episodic memories and plans, are not unique to humans. What is unique is our ability to deliberately transfer these inner simulations to each other, a trick possible only because of language.

The breakthrough of mentalizing enabled early primates to learn from other people’s actual actions (imitation learning). But the breakthrough of speaking uniquely enabled early humans to learn from other people’s imagined actions.

The true power of DNA is not the products it constructs (hearts, livers, brains) but the process it enables (evolution). In this same way, the power of language is not its products (better teaching, coordinating, and common myths) but the process of ideas being transferred, accumulated, and modified across generations. Just as genes persist by hopping from parent cell to offspring cell, ideas persist by hopping from brain to brain, from generation to generation.

Take a four-year-old child and an adult chimpanzee and have them observe an experimenter open a puzzle box to get food, in the process performing several irrelevant actions. Both chimps and human children learn to open the puzzle box through observation; however, chimps will skip the irrelevant steps, but human children will perform all the steps they observed, including the irrelevant ones. Human children are over-imitators. This over-imitation is, in fact, quite clever. Children change their degree of copying based on how much they believe the teacher knows—“This person clearly knows what she is doing, so there must be a reason she did that.”

communicating how to do a task using language dramatically improves the accuracy and speed with which children solve tasks. Language lets us condense information so it takes up less brain space and can be more quickly transferred from brain to brain.

From a period of seemingly perpetual stasis, you will, in a matter of a few hundred thousand years, get an explosion of complex ideas.

We are the hive-brain apes. We synchronize our inner simulations, turning human cultures into a kind of meta-life-form whose consciousness is instantiated within the persistent ideas and thoughts flowing through millions of human brains over generations. The bedrock of this hive brain is our language.

Indeed, the incredible ascent of humankind during the past few thousand years had nothing to do with better genes and everything to do with the accumulation of better and more sophisticated ideas.

Leborgne could understand language; he just couldn’t produce it.

Leborgne had brain damage to a specific and isolated region in the left frontal lobe. Broca had a hunch that there were specific areas in the brain for language.

It turned out that all of these patients had damage to similar regions on the left side of the neocortex, a region that has come to be called Broca’s area. This has been observed countless times over the past hundred and fifty years—if Broca’s area is damaged, humans lose the ability to produce speech, a condition now called Broca’s aphasia.

Wernicke, following Broca’s strategy, also found a damaged area in the brains of these patients. It was also on the left side but farther back in the posterior neocortex, a region now dubbed Wernicke’s area. Damage to Wernicke’s causes Wernicke’s aphasia, a condition in which patients lose the ability to understand speech.

Patients with Broca’s aphasia become equally impaired in speaking words as they are in writing words.

language emerges not from the brain as a whole but from specific subsystems.

Language is a specific and independent skill that evolution wove into our brains. So this would seem to close the case. We have found the language organ of the human brain: humans evolved two new areas of neocortex—Broca’s and Wernicke’s areas—which are wired together into a specific subnetwork specialized for language. This subnetwork gifted us language, and that is why humans have language and other apes don’t.

Unfortunately, the story is not so simple.

it was not the emergence of Broca’s or Wernicke’s areas that gave humans the gift of language. Perhaps human language was an elaboration on the existing system of ape communication? This might explain why these language areas are still present in other primates.

It turned out that this teacher had a lesion in his brain stem that had disrupted the connection between his neocortex and the muscles on the left side of his face but had spared the connection between his amygdala and those same muscles. This meant that he couldn’t voluntarily control the left side of his face, but his emotional-expression system could control his face just fine. While he was unable to voluntarily lift an eyebrow, he was eminently able to laugh, frown, and cry.

Even individuals who can’t utter a single word can readily laugh and cry. Why? Because emotional expressions emerge from a system entirely separate from language.

Human laughs, cries, and scowls are evolutionary remnants of an ancient and more primitive system for communication, a system from which ape hoots and gestures emerge.

This explains why lesions to Broca’s and Wernicke’s areas in monkeys have absolutely no impact on communication. A monkey can still hoot and holler for the same reason a human with such damage can still laugh, cry, smile, frown, and scowl even while he can’t utter a single coherent word. The gestures of monkeys are automatic emotional expressions and don’t emerge from the neocortex; they are more like a human laugh than language.

The emotional-expression system and the language system have another difference: one is genetically hardwired, and the other is learned.

monkeys who are raised in isolation still end up producing all of their normal gesture-call behavior, and chimpanzees and bonobos share almost 90 percent of the same gestures. Similarly, human cultures and children from around the world have remarkable overlap in emotional expressions, suggesting that at least some parts of our emotional expressions are genetically hard-coded and not learned.

However, the newer language system in humans is incredibly sensitive to learning—if a child goes long enough without being taught language, he or she will be unable to acquire it later in life.

So here is the neurobiological conundrum of language. Language did not emerge from some newly evolved structure. Language did not emerge from humans’ unique neocortical control over the larynx and face (although this did enable more complex verbalizations). Language did not emerge from some elaboration of the communication systems of early apes. And yet, language is entirely new.

But if flying is not genetically hard-coded, then how is it that approximately 100 percent of all baby birds independently learn such a complex skill? A skill as sophisticated as flying is too information-dense to hard-code directly into a genome. It is more efficient to encode a generic learning system (such as a cortex) and a specific hardwired learning curriculum (instinct to want to jump, instinct to flap wings, and instinct to attempt to glide). It is the pairing of a learning system and a curriculum that enables every single baby bird to learn how to fly.

TD-Gammon enabled a computer to outperform humans in the game of backgammon. I left out a crucial part of how TD-Gammon was trained. It did not learn through the trial and error of endless games of backgammon against a human expert. If it had done this, it would never have learned, because it would never have won. TD-Gammon was trained by playing against itself. TD-Gammon always had an evenly matched player. This is the standard strategy for training reinforcement learning systems.

To teach a new skill, it is often easier to change the curriculum instead of changing the learning system. Indeed, this is the solution that evolution seems to have repeatedly settled on when enabling complex skills—monkey climbing, bird flying, and, yes, even human language all seem to work this way. They emerge from newly evolved hardwired curriculums.

Newer studies are even calling into question the idea that Broca’s and Wernicke’s areas are actually the loci of language; language areas may be located all over the neocortex and even in the basal ganglia. Here is the point: There is no language organ in the human brain, just as there is no flight organ in the bird brain.

Such complex skills are not localized to a specific area; they emerge from a complex interplay of many areas. What makes these skills possible is not a single region that executes them but a curriculum that forces a complex network of regions to work together to learn them.

What is unique in the human brain is not in the neocortex; what is unique is hidden and subtle, tucked deep in older structures like the amygdala and brain stem. It is an adjustment to hardwired instincts that makes us take turns, makes children and parents stare back and forth, and that makes us ask questions.

We know that the breakthrough that makes the human brain different is that of language. It is powerful because it allows us to learn from other people’s imaginations and allows ideas to accumulate across generations.

And we know that language emerges in the human brain through a hardwired curriculum to learn it that repurposes older mentalizing neocortical areas into language areas.

language, at least as far as we know, has emerged only once. Why?

brains stayed largely the same size until around two and a half million years ago, at which point something mysterious and dramatic happened. The human brain rapidly became over three times larger and earned its place as one of the largest brains on Earth.

some mysterious force more than two million years ago triggered a “runaway growth of the brain.” Why exactly this happened is an outstanding question in paleoanthropology.

there is still more than enough evidence for scientists to reconstruct the basics of our general story. It begins with a dying forest.

At some point around six million years ago, these new mountains became so sprawling that they separated the ape ancestors on each side of the Great Rift Valley, splitting them into two separate lineages. On the western side, in an environment still rich with forests and largely unchanged, the lineage remained similarly unchanged and became today’s chimpanzees. On the eastern side of the mountains, however, in an environment of dying trees and progressively more open grasslands, evolutionary pressures began tinkering. It was this lineage that would eventually become human.

Fossils of our upright-walking ancestors from around four million years ago reveal a brain still the size of a modern chimpanzee’s.

Our ancestors were, in essence, upright-walking chimpanzees.

By two and a half million years ago, the new African savannah had become heavily populated with massive herbivorous mammals; ancestral elephants, zebras, giraffes, and hogs wandered and grazed.

amid this cacophonous zoo of large mammals was a humble ape who had been displaced from its comfortable forest habitat. And this humble ape—our ancestor—would have been searching for a new survival niche in this ecosystem brimming with armies of giant herbivores and carnivorous hunters.

Our ancestors began shifting toward eating meat. Only about 10 percent of the diet of a chimpanzee comes from meat, while evidence suggests that as much as 30 percent of the diet of these early humans came from meat.

These ancestors invented stone tools that seemed to be used specifically for processing the meat and bones of carcasses. These tools are referred to as “Oldowan tools” after the location where they were discovered (Olduvai Gorge in Tanzania).

Fast-forward five hundred thousand years, and our ancestors in eastern Africa had evolved into a species called Homo erectus, meaning “upright man” (which is a silly name, since our ancestors were walking upright well before Homo erectus).

While earlier humans were timid vultures, Homo erectus was an apex predator. Homo erectus became a hypercarnivore, consuming a diet that was an almost absurd 85 percent meat.

Most notable, H. erectus had a brain that was twice the size of our ancestral upright-walking-chimpanzee-like ancestor’s from a million years prior. At least one benefit of this bigger brain was better tools: H. erectus invented a new class of sharp stone hand axes. Their shoulders and torsos became uniquely adapted for throwing.