How special are human brains among animal brains?

by zhukeepa7 min read1st Apr 202038 comments

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BiologyGeneral IntelligenceAI TimelinesConsciousnessNeuroscience
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Crossposted from the AI Alignment Forum. May contain more technical jargon than usual.

Humans are capable of feats of cognition that appear qualitatively more sophisticated than those of any other animals. Is this appearance of a qualitative difference indicative of human brains being essentially more complex than the brains of any other animal? Or is this “qualitative difference” illusory, with the vast majority of human cognitive feats explainable as nothing more than a scaled-up version of the cognitive feats of lower animals?

“How special are human brains among animal brains?” is one of the background variables in my framework for AGI timelines. My aim for this post is not to present a complete argument for some view on this variable, so much as it is to:

  • present some considerations I’ve encountered that shed light on this variable
  • invite a collaborative effort among readers to shed further light on this variable (e.g. by leaving comments about considerations I haven’t included, or pointing out mistakes in my analyses)

Does mastery of language make humans unique?

Human conscious experience may have emerged from language

Humans seem to have much higher degrees of consciousness and agency than other animals, and this may have emerged from our capacities for language. Helen Keller (who was deaf and blind since infancy, and only started learning language when she was 6) gave an autobiographical account of how she was driven by blind impetuses until she learned the meanings of the words “I” and “me”:

Before my teacher came to me, I did not know that I am. I lived in a world that was a no-world. I cannot hope to describe adequately that unconscious, yet conscious time of nothingness. I did not know that I knew aught, or that I lived or acted or desired. I had neither will nor intellect. I was carried along to objects and acts by a certain blind natural impetus. I had a mind which caused me to feel anger, satisfaction, desire. These two facts led those about me to suppose that I willed and thought. I can remember all this, not because I knew that it was so, but because I have tactual memory. It enables me to remember that I never contracted my forehead in the act of thinking. I never viewed anything beforehand or chose it. I also recall tactually the fact that never in a start of the body or a heart-beat did I feel that I loved or cared for anything. My inner life, then, was a blank without past, present, or future, without hope or anticipation, without wonder or joy or faith.
[...]
… When I learned the meaning of "I" and "me" and found that I was something, I began to think. Then consciousness first existed for me. Thus it was not the sense of touch that brought me knowledge. It was the awakening of my soul that first rendered my senses their value, their cognizance of objects, names, qualities, and properties. Thought made me conscious of love, joy, and all the emotions. I was eager to know, then to understand, afterward to reflect on what I knew and understood, and the blind impetus, which had before driven me hither and thither at the dictates of my sensations, vanished forever.

Mastery of language may have conferred unique intellectual superpowers

I think humans underwent a phase transition in their intellectual abilities when they came to master language, at which point their intellectual abilities jumped far beyond those of other animals on both an individual level and a species level.

On an individual level, our capacity for language enables us to entertain and express arbitrarily complex thoughts, which appears to be an ability unique to humans. In theoretical linguistics, this is referred to as “digital infinity”, or “the infinite use of finite means”.

On a species level, our mastery of language enables intricate insights to accumulate over generations with high fidelity. Our ability to stand on the shoulders of giants is unique among animals, which is why our culture is unrivaled in its richness in sophistication.

Language aside, how unique are humans?

Humans ≈ Neanderthals + language?

The most quintessentially human intellectual accomplishments (e.g. proving theorems, composing symphonies, going into space) were only made possible by culture post-agricultural revolution. So, when evaluating humans’ innate intellectual capacities, a better reference point than modern humans like ourselves would be our hunter-gatherer ancestors.

We can reduce the question of how complex our hunter-gatherer ancestors’ brains are into two sub-questions: how complex is our capacity for mastering language, and how complex are brains that are similar to ours, but don’t have the capacity for mastering language?

Neanderthal brains seem like plausible proxies for the latter. Neanderthals are similar enough to modern humans that they’ve interbred, and the currently available evidence suggests that they may not have mastered language in the same way that behaviorally modern humans have. (I don’t think this evidence is very strong, but this doesn’t matter for my purposes—I’m just using Neanderthals as a handy stand-in to gesture at what a human-like intelligence might look like if it didn’t have the capacity for language.)

Higher intelligence in animals

Chimpanzees, crows, and dolphins are capable of impressive feats of higher intelligence, and I don’t think there’s any particular reason to think that Neanderthals are capable of doing anything qualitatively more impressive. I’ll share some examples of these animals’ intellectual feats that I found particularly illustrative.

Chimpanzees have been observed to lie to each other under experimental conditions. From Wikipedia:

...food was hidden and only one individual, named Belle, in a group of chimpanzees was informed of the location. Belle was eager to lead the group to the food but when one chimpanzee, named Rock, began to refuse to share the food, Belle changed her behaviour. She began to sit on the food until Rock was far away, then she would uncover it quickly and eat it. Rock figured this out though and began to push her out of the way and take the food from under her. Belle then sat farther and farther away waiting for Rock to look away before she moved towards the food. In an attempt to speed the process up, Rock looked away until Belle began to run for the food. On several occasions he would even walk away, acting disinterested, and then suddenly spin around and run towards Belle just as she uncovered the food.

In Aesop’s fable of the crow and the pitcher, a thirsty crow figures out that it can drop pebbles into a pitcher, so that the water rises to a high enough level for it to drink from. This behavior has been experimentally replicated, indicating that crows have a “sophisticated, but incomplete, understanding of the causal properties of displacement, rivalling that of 5–7 year old children”.

When Kelly the dolphin was given rewards of fish for picking up scraps of paper, “Kelly figured out that she received the same fish regardless of the size of the piece of trash she was delivering to her trainer. So she began hiding big pieces of trash under a rock. Kelly would then rip off small pieces from the trash and deliver them one at a time so that she could receive more fish.” Additionally, “when a bird landed in the pool, Kelly snatched it and delivered it to her trainers. She received a large amount of fish in return. Knowing this, she decided to start hiding fish each time she was fed. She would then use the fish to lure birds when none of her trainers were around. Kelly knew that by saving one or two fish now, she could get many more fish later by turning in a bird.“ (Also reported on The Guardian; I don’t know how reputable these sources are, so take this anecdote with a grain of salt.)

See these Wikipedia pages for some more interesting examples, and see here for a more thorough review of the evidence of higher intelligence in animals.

“Qualitatively” more advanced cognition may emerge from scale

Many aspects of human cognition that may appear qualitatively different from what other animals are capable of, such as long chains of abstract reasoning, also appear qualitatively different from what less intelligent humans are capable of. As a particularly extreme example, John von Neumann’s cognitive abilities were so advanced that a Nobel Laureate, Hans Bethe, once remarked that "[his] brain indicated a new species, an evolution beyond man".

At the same time, the genes that code for different humans’ brains are virtually identical from an evolutionary perspective. This suggests that the seemingly qualitative differences between humans’ and animals’ cognition might not be so different from the seemingly qualitative differences between John von Neumann’s cognition and mine—our brains might be doing essentially the same thing as theirs, except at a higher scale.

How hard is mastery of language?

Could language capacity fall out from general capacities?

Maybe it was extraordinarily difficult to evolve the cognitive mechanisms that allow us to learn language, above and beyond our cognitive machinery for learning other things. I think this is plausible, but I don’t think the case for this is very strong.

Animals (Washoe, Koko, and Alex the parrot) have demonstrated the ability to learn simple forms of symbolic communication, which they never evolved to do, indicating that their ability to learn things in general is good enough to learn very simple forms of language. It’s true that there are aspects of human language that escape animals, but they also escape feral children, and might escape animals for mundane reasons, like their not having critical periods long enough to learn these aspects of language.

Additionally, AI language models provide evidence that simple and general learning mechanisms can capture many of the intricacies of human language that other animals miss, further suggesting that there’s nothing intrinsically difficult about learning language. Here’s an excerpt from GPT-2, a relatively recent language model:

SYSTEM PROMPT (HUMAN-WRITTEN)
In a shocking finding, scientist discovered a herd of unicorns living in a remote, previously unexplored valley, in the Andes Mountains. Even more surprising to the researchers was the fact that the unicorns spoke perfect English.
MODEL COMPLETION (MACHINE-WRITTEN, 10 TRIES)
The scientist named the population, after their distinctive horn, Ovid’s Unicorn. These four-horned, silver-white unicorns were previously unknown to science.
Now, after almost two centuries, the mystery of what sparked this odd phenomenon is finally solved.
Dr. Jorge Pérez, an evolutionary biologist from the University of La Paz, and several companions, were exploring the Andes Mountains when they found a small valley, with no other animals or humans. Pérez noticed that the valley had what appeared to be a natural fountain, surrounded by two peaks of rock and silver snow.
Pérez and the others then ventured further into the valley. “By the time we reached the top of one peak, the water looked blue, with some crystals on top,” said Pérez.

Why haven’t other species mastered language?

If language isn’t a particularly difficult cognitive capacity to acquire, why don’t we see more animal species with language?

One possibility is that the first species that masters language, by virtue of being able to access intellectual superpowers inaccessible to other animals, has a high probability of becoming the dominant species extremely quickly. (Humans underwent the agricultural revolution within 50,000 years of behavioral modernity—a blink of an eye on evolutionary timescales—after which their dominance as a species became unquestionable.) Since we shouldn’t expect to see more than one dominant species at a time, this would imply a simple anthropic argument for our unique capacities for language: we shouldn’t expect to see more than one species at a time with mastery of language, and we just happen to be the species that made it there first.

It may also turn out that language is hard to evolve not because it’s a particularly sophisticated cognitive mechanism, but because the environments that could have supported language and selected for it might have been very unique. For example, it may be that a threshold of general intelligence has to be crossed before it’s viable for a species to acquire language, and that humans are the only species to have crossed this threshold. (Humans do have the highest cortical information processing capacity among mammals.)

It might also turn out that the cultural contexts under which language could evolve require a mysteriously high degree of trust: “... language presupposes relatively high levels of mutual trust in order to become established over time as an evolutionarily stable strategy. This stability is born of a longstanding mutual trust and is what grants language its authority. A theory of the origins of language must therefore explain why humans could begin trusting cheap signals in ways that other animals apparently cannot (see signalling theory).”

My current take

As we came to master language, I think we underwent a phase transition in our intellectual abilities that set us apart from other animals. Besides language, I don't see much that sets us apart from other animals—in particular, most other cognitive differences seem explainable as consequences of either language or scale, and I don’t think the cognitive mechanisms that allow us to master language are particularly unique or difficult to acquire. Overall, I don’t see much reason to believe that human brains have significantly more innate complexity than the brains of other animals.


Thanks to Paul Kreiner and Stag Lynn for helpful commentary and feedback.

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