Cognitive Science: An Introduction/Explanations For How Humans Got So Smart

Human beings are enormously successful on Earth, biologically speaking. Other creatures are also successful, but they do this primarily through speciation--a new species will evolve to occupy a different environment. Ants, for example, are all over the planet, but to do this they evolved into more than 14,000 different species. Human beings, on the other hand, can live in many environments that differ enormously, from the Arctic to the desert, to the rain forest, without a great amount of genetic evolution.

Generally, the accepted reason why humans are so successful is that we are more intelligent than any other species. But what exactly this means, and especially how we got like this, remains an area of significant scientific controversy.

If we look at our ancestors, we can measure their brain size by looking at fossil skulls. Homo erectus had a cranial capacity of 930 cubic centimeters. Our species, Homo sapiens has an average of 1,330 cubic centimeters. In particular, our frontal areas changed, consistent with the view that our old brain stayed relatively the same while the new brain areas changed rapidly. Human brains consume an enormous amount of energy--about 20-25% of the energy we take in goes to running the brain. This is really high compared to other animals, such as other primates (8-10%), or other mammals (3-5%).

How did human brains get so big?

It's easy to think of evolution being purely a genetic thing that's completely separate from culture. But cultural change can affect genetic change, and vice versa. It's possible that our ancestors engaged in what is called cultural ratcheting: the culture changes, which changes our genetic makeup, which changes our culture, and so on. A single gene has been found in humans, but not in chimps, that might explain a great deal of the massive number of neurons in human brains.

Humans Are Built to Learn

Some animals can start taking care of themselves as soon as they are born. There are some birds, for example, that, immediately upon hatching, start pecking around, eating seeds. Think about human babies: they are helpless, and need constant care and attention, for a very long time. Those birds are what we'd call "precocious," and humans are more "altricious."

Although it seems like it would be better to be born with more competence, there is a tradeoff that benefits human beings a lot. Because they are not born with lots of built-in knowledge, humans have to learn how to live in the world over time. The benefit of this is that humans can adapt to many environments, both physical and cultural. As a result, humans can live just about anywhere on Earth. Birds come ready to find seeds, but if they are born in an environment without seeds on the ground, they are out of luck. In contrast, during their long development, humans learn to get food however they need to, according to the culture and environment they are born in.

How did humans come to be born with such a propensity for learning? It is likely that this is because our brains are born small. Although the relationship between brain size and intelligence is controversial when looking at which person is smarter than another, there seems to be a clear relationship between brain size and intelligence across species. More specifically, it's the ratio between brain size and body size: the bigger the brain is, in proportion to the size of the organism's body, the smarter it tends to be.

Human brains are very big compared to body size. For humans, our evolutionary niche seems to be tied to our intelligence. We're not the strongest, or most numerous creatures on the planet, but we are the smartest. For this a big brain is necessary.

The problem is that giving birth to a big-brained baby requires a large pelvis, and if a woman's pelvis is too large she won't be able to run properly, due to our upright posture (animals that run on all fours don't have quite the same issue). If she can't run, she might not survive to have any children. So there is evolutionary pressure to make women's pelvises bigger (for giving birth to smart babies), and a counteracting pressure to make pelvises smaller (so women can run).

There are several interesting results of this trade-off. During childbirth, the pelvis expands and kind of comes apart to accommodate large baby heads. The baby's skull is in pieces at birth. These pieces gradually fuse together. This is why there is a soft spot on a newborn's head that you're not supposed to press. Even with these accommodations, childbirth is very dangerous for human beings: that's how important intelligence is.

But perhaps the most important accommodation is that babies are born with small brains that get bigger over development. The cerebral cortex grows after birth. And in order for this to happen, there needs to be less build-in knowledge at birth. Basically, we evolved to have our babies born kind of premature.

So it appears that an adaptation to allow intelligence as well as an upright posture also allowed human beings to have such a variety of cultures. This also allowed for technological buildup--humans create technology, and the children learn about it as a part of the environment they grow up in, and then they make new technology of their own. We can see how the combination of an upright posture and an arms race for intelligence led to brains being small and altricious at birth, which led to more flexible intelligence in human adults.

In brain evolution, a single mutation can’t cause a new, useful, complex brain area to spring into being. However, a single mutation might cause the replication of another brain region. In rare individuals, this new brain region might get recruited for some other purpose, allowing a survival advantage that might then get passed on. Note that this is only possible for brain regions that learn to work in a certain way--a replicated a hard-coded system would only be able to reproduce the same functionality. This might be a part of why the human brain, and particularly the cerebral cortex, looks kind of the same all over.

So why was there an arms race of intelligence in humans, but not in all species? There are several theories. One we will discuss relates to social reasoning.

The Cultural Intelligence Hypothesis: Humans Developed The Ability to Have Cumulative Cultural Knowledge

Unprocessed Foods: Many people think that food it better if it's natural and unprocessed, but this is a view only possible in a world with grocery stores, where the food you see has been preprocessed and bred for human consumption. Many foods people eat in natural environments require enormous amounts of processing to make them edible. Even beans can be toxic without processing, as were early potatoes before they were artificially bred to the food we enjoy totday. When people say one should eat unprocessed foods, perhaps they should mean industrial processes, rather than those done more or less by hand.

Related to learning and social intelligence (below), another theory is that it isn't raw intelligence or learning that makes us special, it is that the ability to learn from and teach each other that differentiates us from other species. The spectacular success that humans have enjoyed is due not to our ability to figure out and solve problems better than other species, but that culture, over time, comes up with the solutions that often no individual in the culture really understands. We're smart because of the culture, not the other way around, according to this theory. What we have that is special is the ability to learn and teach each other skills and knowledge.

There are several lines of evidence that support this view.

The things that people do to thrive in an environment are often too complex for a single individual or group of individuals to figure out. People learn how to survive in their environments through both individual learning, and social learning from others in the culture. How do we know this is true? When we look at lose European explorers, we see the only ones who survived were the ones who learned how to from the native peoples of the area. For all of the intelligence in their big brains, in general they could not figure out the complex skills required to survive.

Let's take an example of one of the staple crops of the tropical environments, manioc.

A bowl of dried manioc.

There are many steps required to transform manioc from its natural state to something that can be safely eaten. Here is what the Tukanoans of the Colombian Amazon do: the manioc is scraped, grated, and washed to separate the starch, fiber, and liquid. The liquid is boiled into a beverage and can be drank. The fiber and starch sits for two days, then is baked and eaten. Failure to do it like this causes long-term cyanide poisoning, but this only builds up over years, and the dangerous manioc does not taste any differently. With this example, it is easy to see how difficult it might be for a single person, or even a single group of smart people working together, could figure this out. The health problems only show up decades later. Cultures "figure it out" over time, and many people in the culture don't even know exactly whey they are doing the steps they do. Using critical thinking, and cutting out parts of this process on the basis of not knowing what they are for would lead to death. Indeed, in places where manioc has been brought to other continents, but without the processing technique, there are problems with cyanide poisoning. Many people, it seems, still have not figured it out.

There are even instances where knowing how a process works would make it work more poorly. Naskapi hunters use a form of divination to determine where to hunt caribou. They heat a bone over coals and interpret the cracking. The process is random, but this actually helps the hunters, because people would naturally want to hunt where recent hunts have been successful. But caribou avoid these locations for the same reasons. So not only is using the divination helpful for the hunters, but it works only because it is a random process--in a sense, it works because it doesnt' work, and knowing that it was a random process might make them not use it, and hurt their abilities to successfully hunt.

This theory suggests that we are successful for being smart in a particular way: we developed the ability to learn from others. This is supposed to have happened in our genus about two million years ago. Provacatively, some have even suggested that Neanderthals were smarter than human beings, because they had bigger brains, and the intelligence of a primate is predicted best by brain size, but what they lacked was the ability to effectively transmit cultural innovations as well as human beings, who had more interconnected social groups and longer lifespans. This is thought to have happened only a few million years ago.

REM Sleep

Another theory is that coming out of the trees allowed for more REM sleep.

Sleeping in trees has inherent danger from falling. Sleeping on the ground avoids this danger, but presents others.

Jaguar sleeping in a tree.

Panthera onca -sleeping in tree -Belize Zoo-8.jpg

In particular, sleeping on the ground allows for more REM sleep.

Social Intelligence

One theory of how humans became so intelligent so fast involves social cognition. Human beings are social creatures, and have lived in intensely social, hierarchical societies since at least the dawn of agriculture.

Human survival and reproduction was, and continues to be, dependent on living in a complex social world. The idea is that those better at navigating this social world out-survived and out-reproduced those who were worse at it.

One way to think about the depth of social cognition an agent can engage in is to think about representing other agent's mindsets. For example, you might believe that your mother believes that you're in university. That's going one level deep. But if you believe that your mother believes that you believe that you're doing well in school, that's two levels. How deep can people reason in this way?

Studies of reading fiction suggest that people have a lot of trouble comprehending stories that go beyond the fourth level. Another interesting source of evidence for depth of belief processing comes from behavioral economics. Imagine you are a member of a group of people, and everybody has to choose a number between 1 and 100. The winner is the person who guesses the number closest to 2/3 of the average number. So if the average number was 60, then the winning number would be the one closest to 40. What is the most rational number to choose? Well, if you figure that the average number chosen will be 50, then you might want to pick 33. But if you assume that others are rational too, then you'd know that others would also pick 33, then you'd want to pick 2/3 of that number! How far should you go? If you assume everyone is perfectly rational, then you should pick the number 1.

But when this experiment is done in practice, people only use 1 or 2 steps of induction. The best strategy is to go just one level further than most other people will.

Mark Thomas has a theory that we started living in larger groups, which make the probability of an innovation in a given group greater (simply because there were more people). Computer models show that group sizes tend to get bigger at the same time innovation appears. Cultural innovation requires people communicating.

A related idea is the "Machiavellian Intelligence Hypothesis," which holds that we evolved to be smart so that we could better deceive and manipulate people.

Group Hunting

A related idea is that we had to get smarter to do coordinated group hunting missions, which requires some social intelligence. Human beings are very good hunters, and are specialized in several ways.

Humans can run for long distances. Few other animals can do this, in part because they overheat. Horses can run long distances, but this is in part because we bred them that way. Human beings have far more eccrine glands, which sweat and keep us cool. Other pack hunting animals, such as hyena, can't keep cool as well, and as such hunt at dusk and dawn (they are crepuscular), when they can see but it's not too hot. Human hunters, on the other hand, tend to hunt when it's hottest: at mid-day. Humans can track, carry water, coordinate their activities, and sweat. Often human's prey simply falls over from over-heating or exhaustion.

Hunting not only encouraged the need for socialization during the hunt, but after as well. It is very hard for an individual or a group of individuals to consistently hunt meat. Kills are infrequent and unpredictable. However, a wild bull killed by a hunting party of six can feed 1000 people. Cultural practiced developed to share meat. Infrequent kills by various hunting groups resulted in a stable meat consumption for a large group. But navigating this, and making sure people aren't being free-riders requires more social intelligence and culture.

Effective hunting encouraged social groups, provided more calories for use in brain development, upright posture, tool use (water vessels and weapons), and encouraged good visual systems.

Tool Use and Hand Theory

One theory is that tool creation and use encouraged larger brains. In support of this, we naturally categorize human-made things (artifacts) separately from other things in the world, like rocks and plants. We naturally think about function with tools.

Human beings evolved from arboreal species, or creatures that lived in trees. Although the hands needed for navigating branches are useful, they do not need to be very precise. The precision grip that humans can do seems to be a function, in part, of our becoming a more terrestrial species (that is, living on land more often.)

Being on the ground allows you to leave tools and parts around within easy reach--something difficult to do up in a tree. Chimpanzees use simple tools, and the tools they use on the ground are more complex than the ones they use in trees. Not needing to use your hands to navigate frees them up for other purposes, allowing them to evolve to be better at building and using tools.

But some have pointed out that the increase in brain size does not correlate well with the archaeological record of tool construction. The improved tool designs of the Upper Paleolithic thus might be a consequence, and not a cause, of a larger brain. One theorized solution to this problem is that human beings fare better not because they are so smart, but because they are such good cultural learners (see the section on Cumulative Cultural Evolution on this page.)

Tool use encourages cultural learning, upright posture, more hand-like hands, living on the ground instead of in the trees, and long-term planning.

Cooking

Although our ancestors might have been using fire up to 800,000 years ago, fire's use was widespread for "Homo erectus, neanderthals," and ancestors of "Homo sapiens" about 30,000 years ago. This allowed for cooking, which had influences on human intelligence.

There is no evidence, however, that human beings innately know how to cook or to make fire. Some societies have the cultural know-how to create fire at one point, and then lose it at some later point.

How could cooking affect our intelligence? First, we had to spend less time chewing. Whereas chimpanzees spend about five hours every day chewing food, humans only take one hour a day. This allows time for other activities.

Second, it allowed us to have smaller teeth and shorter intestines. This caused energy savings that could then be used by our energy-hungry brains. Cooking externalized digestion, in that much of the processing that has to be done to food to make it digestible is often done inside the organism, but in humans, it's done by cooking and other cultural practices. The calories humans consume could then be put to bigger brains, rather than complex digestive tracts. Cooking food increases its available energy. Other animals, such as chimpanzees, can eat a raw diet without problems, but humanity's dependence on cooking is reflected in the fact that humans who eat only raw food are often thin and hungry--sometimes women's body fat gets so low that they stop menstruating.

This is a good example of culture affecting evolution: the use of fire is a cultural and technological advance, and its widespread use allowed evolution to change our bodies.

Is Intelligence Adaptive?

Overall, greater intelligence is almost certainly adaptive. In humans, higher IQ correlates with reduced disease, accidents, and suicide, and increased longevity. However, in modern industrialized societies, more intelligent people have children later and fewer than less intelligent people. This highlights the fact that the notion of survival of the fittest is more appropriately thought of as reproduction of the fittest, in terms of what matters for evolution.

The Recent Decrease in Human Brain Size

Although human brains underwent an explosion in size, for the last 10 or 20 thousand years, our brains have actually gotten smaller. We don't know exactly why, but here are some ideas. First, it might be because our bodies have gotten smaller. Larger bodies require larger nervous systems for maintenance. Our bodies have gotten a bit smaller, perhaps due, in part, to increasing temperatures (larger bodies conserve heat better), or because we have been domesticating ourselves (domestic creatures are smaller). Smaller bodies also mean a smaller pelvis size, which would require smaller heads for safe childbirth. Another reason might be that we have started to store knowledge externally, in books (and now computers, but that is evolutionarily very recent). It could be that this has allowed evolution to favor a more efficient brain. It might be that larger brains are less efficient at certain tasks, because the longer neural pathways that information must travel would hinder fast thought.