Animal Intelligence and the Evolution of the Human Mind

Subtle refinements in brain architecture, rather than large-scale alterations, make us smarter than other animals

By Ursula Dicke and Gerard Roth

As far as we know, no dog can compose music, no dolphin can speak in rhymes, and no parrot can solve equations with two unknowns. Only humans can perform such intellectual feats, presumably because we are smarter than all other animal species—at least by our own definition of intelligence.

Of course, intelligence must emerge from the workings of the three-pound mass of wetware packed inside our skulls. Thus, researchers have tried to identify unique features of the human brain that could account for our superior intellectual abilities. But, anatomically, the human brain is very similar to that of other primates because humans and chimpanzees share an ancestor that walked the earth less than seven million years ago.

Accordingly, the human brain contains no highly conspicuous characteristics that might account for the species’ cleverness. For instance, scientists have failed to find a correlation between absolute or relative brain size and acumen among humans and other animal species. Neither have they been able to discern a parallel between wits and the size or existence of specific regions of the brain, excepting perhaps Broca’s area, which governs speech in people. The lack of an obvious structural correlate to human intellect jibes with the idea that our intelligence may not be wholly unique: studies are revealing that chimps, among various other species, possess a diversity of humanlike social and cognitive skills.

Nevertheless, researchers have found some microscopic clues to humanity’s aptitude. We have more neurons in our brain’s cerebral cortex (its outermost layer) than other mammals do. The insulation around nerves in the human brain is also thicker than that of other species, enabling the nerves to conduct signals more rapidly. Such biological subtleties, along with behavioral ones, suggest that human intelligence is best likened to an upgrade of the cognitive capacities of nonhuman primates rather than an exceptionally advanced form of cognition.

Smart Species
Because animals cannot read or speak, their aptitude is difficult to discern, much less measure. Thus, comparative psychologists have invented behavior-based tests to assess birds’ and mammals’ abilities to learn and remember, to comprehend numbers and to solve practical problems. Animals of various stripes—but especially nonhuman primates—often earn high marks on such action-oriented IQ tests. During World War I, German psychologist Wolfgang Köhler, for example, showed that chimpanzees, when confronted with fruit hanging from a high ceiling, devised an ingenious way to get it: they stacked boxes to stand on to reach the fruit. They also constructed long sticks to reach food outside their enclosure. Researchers now know that great apes have a sophisticated understanding of tool use and construction.

Psychologists have used such behavioral tests to illuminate similar cognitive feats in other mammals as well as in birds. Pigeons can discriminate between male and female faces and among paintings by different artists; they can also group pictures into categories such as trees, selecting those belonging to a category by pecking with their beaks, an action that often brings a food reward. Crows have intellectual capacities that are overturning conventional wisdom about the brain.

Behavioral ecologists, on the other hand, prefer to judge animals on their street smarts—that is, their ability to solve problems relevant to survival in their natural habitats—rather than on their test-taking talents. In this view, intelligence is a cluster of capabilities that evolved in response to particular environments. Some scientists have further proposed that mental or behavioral flexibility, the ability to come up with novel solutions to problems, is another good measure of animal intellect. Among birds, green herons occasionally throw an object in the water to lure curious fish—a trick that, ornithologists have observed, has been reinvented by groups of these animals living in distant locales. Even fish display remarkable practical intelligence, such as the use of tools, in the wild. Cichlid fish, for instance, use leaves as “baby carriages” for their egg masses.

Animals also can display humanlike social intelligence. Monkeys engage in deception, for example; dolphins have been known to care for another injured pod member (displaying empathy), and a whale or porpoise may recognize itself in the mirror. Even some fish exhibit subtle kinds of social skills. Behavioral ecologist Redouan Bshary of the University of Neuchâtel in Switzerland and his colleagues described one such case in a 2006 paper. Bony fish such as the so-called cleaner wrasse (Labroides dimidiatus) cooperate and remove parasites from the skin of other fish or feed on their mucus. Bshary’s team found that bystander fish spent more time next to cleaners the bystanders had observed being cooperative than to other fish. Humans, the authors note, tend to notice altruistic behavior and are more willing to help do-gooders whom they have observed doing favors for others. Similarly, cleaner wrasses observe and evaluate the behavior of other finned ocean denizens and are more willing to help fish that they have seen assisting third parties.

From such studies, scientists have constructed evolutionary hierarchies of intelligence. Primates and cetaceans (whales, dolphins and porpoises) are considered the smartest mammals. Among primates, humans and apes are considered cleverer than monkeys, and monkeys more so than prosimians. Of the apes, chimpanzees and bonobos rank above gibbons, orangutans and gorillas. Dolphins and sperm whales are supposedly smarter than nonpredatory baleen whales such as blue whales. Among birds, scientists consider parrots, owls and corvids (crows and ravens) the brightest. Such a pecking order argues against the idea that intelligence evolved along a single path, culminating in human acumen. Instead intellect seems to have emerged independently in birds and mammals and also in cetaceans and primates.

Heavy Thoughts?
What about the brain might underlie these parallel paths to astuteness? One candidate is absolute brain size. Although many studies have linked brain mass with variations in human intelligence, size does not always correlate with smarts in different species. For example, clever small animals such as parrots, ravens, rats and relatively diminutive apes have brains of modest proportions, whereas some large animals such as horses and cows with large brains are comparatively dim-witted. Brain bulk cannot account for human intelligence either: At eight to nine kilograms, sperm and killer whale brains far outweigh the 1.4 kilograms of neural tissue inside our heads. As heavy as five kilograms, elephant brains are also much chunkier than ours.

Relative brain size—the ratio of brain to body mass—does not provide a satisfying explanation for interspecies differences in smarts either. Humans do compare favorably with many medium and large species: our brain makes up approximately 2 percent of our body weight, whereas the blue whale’s brain, for instance, is less than one 100th of a percent of its weight. But some tiny, not terribly bright animals such as shrews and squirrels win out in this measure. In general, small animals boast relatively large brains, and large animals harbor relatively small ones. Although absolute brain mass increases with body weight, brain mass as a proportion of body mass tends to decrease with rising body weight.

Another cerebral yardstick that scientists have tried to tie to intelligence is the degree of encephalization, measured by the encephalization quotient (EQ). The EQ expresses the extent to which a species’ relative brain weight deviates from the average in its animal class, say, mammal, bird or amphibian. Here the human brain tops the list: it is seven to eight times larger than would be expected for a mammal of its weight. But EQ does not parallel intellect perfectly either: gibbons and some capuchin monkeys have higher EQs than the more intelligent chimpanzees do, and even a few pro­sim­ians—the earliest evolved primates alive today—have higher EQs than gorillas do.

Or perhaps the size of the brain’s outermost layer, the cerebral cortex—the seat of many of our cognitive capacities—is the key. But it turns out that the dimensions of the cerebral cortex depend on those of the entire brain and that the size of the cortex constitutes no better arbiter of a superior mind. The same is true for the prefrontal cortex, the hub of reason and action planning. Although some brain researchers have claimed in the past that the human prefrontal cortex is exceptionally large, recent studies have shown that it is not. The size of this structure in hu­mans is comparable to its size in other ­primates and may even be relatively small as compared with its counterpart in elephants and cetaceans.

The lack of a large-scale measure of the human brain that could explain our performance may reflect the idea that human intellect may not be totally inimitable. Apes, after all, understand cause and effect, make and use tools, produce and comprehend language, and lie to and imitate others. These primates may even possess a theory of mind—the ability to understand another animal’s mental state and use it to guide their own behavior. Whales, dolphins and even some birds boast some of these mental talents as well. Thus, adult humans may simply be more intuitive and facile with tools and language than other species are, as opposed to possessing unique cognitive skills.

Networking
Fittingly, researchers have found the best correlates for intelligence by looking at a much smaller scale. Brains consist of nerve cells, or neurons, and supporting cells called glia. The more neurons, the more extensive and more productive the neuronal networks can be—and those networks determine varied brain functions, including perception, memory, planning and thinking. Large brains do not automatically have more neurons; in fact, neuronal density generally decreases with increasing brain size because of the additional glial cells and blood vessels needed to support a big brain.

Humans have 11.5 billion cortical neurons—more than any other mammal, because of the human brain’s high neuronal density. Humans have only about half a billion more cortical neurons than whales and elephants do, however—not enough to account for the significant cognitive differences between humans and these species. In addition, however, a brain’s information-processing capacity depends on how fast its nerves conduct electrical impulses. The most rapidly conducting nerves are swathed in sheaths of insulation called myelin. The thicker a nerve’s myelin sheath, the faster the neural impulses travel along that nerve. The myelinated nerves in the brains of whales and elephants are demonstrably thinner than they are in primates, suggesting that information travels faster in the human brain than it does in the brains of nonprimates.

What is more, neuronal messages must travel longer distances in the relatively large brains of elephants and whales than they do in the more compact human brain. The resulting boost in information-processing speed may at least partly explain the disparity in aptitude between humans and other big-brained creatures.

Among humans’ cerebral advantages, language may be the most obvious. Various animals can convey complex messages to other members of their species; they can communicate about objects that are not in sight and relay information about individuals and events. Chimpanzees, gorillas, dolphins and parrots can even understand and use human speech, gestures or symbols in constructions of up to about three words. But even after years of training, none of these creatures develops verbal skills more advanced than those of a three-year-old child.

In humans, grammar and vocabulary all but explode at age three. This timing corresponds with the development of Broca’s speech area in the left frontal lobe, which may be unique to humans. That is, scientists are unsure whether a direct precursor to this speech region exists in the nonhuman primate brain. The absence of an intricately wired language region in the brains of other species may explain why, of all animals, humans alone have a language that contains complex grammar. Researchers date the development of human grammar and syntax to between 80,000 and 100,000 years ago, which makes it a relatively recent evolutionary advance. It was also one that probably greatly enhanced human intellect.

Chips Coming to a Brain Near You

By Lakshmi Sandhana

In this era of high-tech memory management, next in line to get that memory upgrade isn't your computer, it's you.

Professor Theodore W. Berger, director of the Center for Neural Engineering at the University of Southern California, is creating a silicon chip implant that mimics the hippocampus, an area of the brain known for creating memories. If successful, the artificial brain prosthesis could replace its biological counterpart, enabling people who suffer from memory disorders to regain the ability to store new memories.

And it's no longer a question of "if" but "when." The six teams involved in the multi-laboratory effort, including USC, the University of Kentucky and Wake Forest University, have been working together on different components of the neural prosthetic for nearly a decade. They will present the results of their efforts at the Society for Neuroscience's annual meeting in San Diego, which begins Saturday.

The hippocampus of the intact brain (left) receives neural impulses from the environment. The microchip (right), which may be able to help humans build long-term memories, processes the signals from the brain as electrical impulses and sends them back into the hippocampus.

While they haven't tested the microchip in live rats yet, their research using slices of rat brain indicates the chip functions with 95 percent accuracy. It's a result that's got the scientific community excited.

"It's a new direction in neural prosthesis," said Howard Eichenbaum, director of the Laboratory of Cognitive Neurobiology at Boston University. "The Berger enterprise is ambitious, aiming to provide a prosthesis for memory. The need is high, because of the prevalence of memory disorder in aging and disease associated with loss of function in the hippocampus."

Forming new long-term memories may involve such tasks as learning to recognize a new face, or remembering a telephone number or directions to a new location. Success depend on the proper functioning of the hippocampus. While this part of the brain doesn't store long-term memories, it re-encodes short-term memory so it can be stored as long-term memory.

It's the area that's often damaged as a result of head trauma, stroke, epilepsy and neurodegenerative disorders such as Alzheimer's disease. Currently, no clinically recognized treatments exist for a damaged hippocampus and the accompanying memory disorders.

Berger's team began its research by studying the re-encoding process performed by neurons in slices of rat hippocampi kept alive in nutrients. By stimulating these neurons with randomly generated computer signals and studying the output patterns, the group determined a set of mathematical functions that transformed any given arbitrary input pattern in the same manner that the biological neurons do. And according to the researchers, that's the key to the whole issue.

"It's an impossible task to figure out what your grandmother looks like and how I would encode that," said Berger. "We all do a lot of different things, so we can't create a table of all the things we can possibly look at and how it's encoded in the hippocampus. What we can do is ask, 'What kind of transformation does the hippocampus perform?'

"If you can figure out how the inputs are transformed, then you do have a prosthesis. Then I could put that into somebody's brain to replace it, and I don't care what they look at -- I've replaced the damaged hippocampus with the electronic one, and it's going to transform inputs into outputs just like the cells of the biological hippocampus."

Dr. John J. Granacki, director of the Advanced Systems Division at USC, has been working on translating these mathematical functions onto a microchip. The resulting chip is meant to simulate the processing of biological neurons in the slice of rat hippocampus: accepting electrical impulses, processing them and then sending on the transformed signals. The researchers say the microchip is doing exactly that, with a stunning 95 percent accuracy rate.

"If you were looking at the output right now, you wouldn't be able to tell the difference between the biological hippocampus and the microchip hippocampus," Berger said. "It looks like it's working."

The team next plans to work with live rats that are moving around and learning, and will study monkeys later. The researchers will investigate drugs or other means that could temporarily deactivate the biological hippocampus, and implant the microchip on the animal's head, with electrodes into its brain.

"We will attempt to adapt the artificial hippocampus to the live animal and then show that the animal's performance -- dependent in these tasks on an intact hippocampus -- will not be compromised when the device is in place and we temporarily interrupt the normal function of the hippocampus," said Sam A. Deadwyler, "thus allowing the neuro-prosthetic device to take over that normal function." Deadwyler, a professor at Wake Forest University, is working on measuring the hippocampal neuron activity in live rats and monkeys.

The team expects it will take two to three years to develop the mathematical models for the hippocampus of a live, active rat and translate them onto a microchip, and seven or eight years for a monkey. They hope to apply this approach to clinical applications within 10 years. If everything goes well, they anticipate seeing an artificial human hippocampus, potentially usable for a variety of clinical disorders, in 15 years.

Overall, experts find the results promising.

"We are nowhere near applicability," said Boston University's Eichenbaum. "But the next decade will prove whether this strategy is truly feasible."

"There is a big gap in making the microchip work in a slice preparation and getting it to work in a human being," added Norbert Fortin, a neuroscientist from the Cognitive Neurobiology Lab at Boston University. "However, their approach is very methodical, and it is not unreasonable to think that in 15 to 20 years such a chip could help, to some degree, a patient who suffered from hippocampal damage."

Free Will vs. the Programmed Brain

If our actions are determined by prior events, then do we have a choice about anything—or any responsibility for what we do?

By Shaun Nichols

Many scientists and philosophers are convinced that free will doesn’t exist at all. According to these skeptics, everything that happens is determined by what happened before—our actions are inevitable consequences of the events leading up to the action—and this fact makes it impossible for anyone to do anything that is truly free. This kind of anti-free will stance stretches back to 18th century philosophy, but the idea has recently been getting much more exposure through popular science books and magazine articles. Should we worry? If people come to believe that they don’t have free will, what will the consequences be for moral responsibility?

In a clever new study, psychologists Kathleen Vohs at the University of Minnesota and Jonathan Schooler at the University of California at Santa Barbara tested this question by giving participants passages from The Astonishing Hypothesis, a popular science book by Francis Crick, a biochemist and Nobel laureate (as co-discoverer, with James Watson, of the DNA double helix). Half of the participants got a passage saying that there is no such thing as free will. The passage begins as follows: “‘You,’ your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules. Who you are is nothing but a pack of neurons.”
The passage then goes on to talk about the neural basis of decisions and claims that “…although we appear to have free will, in fact, our choices have already been predetermined for us and we cannot change that.” The other participants got a passage that was similarly scientific-sounding, but it was about the importance of studying consciousness, with no mention of free will.

After reading the passages, all participants completed a survey on their belief in free will. Then comes the inspired part of the experiment. Participants were told to complete 20 arithmetic problems that would appear on the computer screen. But they were also told that when the question appeared, they needed to press the space bar, otherwise a computer glitch would make the answer appear on the screen, too. The participants were told that no one would know whether they pushed the space bar, but they were asked not to cheat.

The results were clear: those who read the anti-free will text cheated more often! (That is, they pressed the space bar less often than the other participants.) Moreover, the researchers found that the amount a participant cheated correlated with the extent to which they rejected free will in their survey responses.

Varieties of Immorality

Philosophers have raised questions about some elements of the study. For one thing, the anti-free will text presents a bleak worldview, and that alone might lead one to cheat more in such a context (“OMG, if I’m just a pack of neurons, I have much bigger things to worry about than behaving on this experiment!”). It might be that one would also find increased cheating if you gave people a passage arguing that all sentient life will ultimately be destroyed in the heat death of the universe.

On the other hand, the results fit with what some philosophers had predicted. The Western conception idea of free will seems bound up with our sense of moral responsibility, guilt for misdeeds and pride in accomplishment. We hold ourselves responsible precisely when we think that our actions come from free will. In this light, it’s not surprising that people behave less morally as they become skeptical of free will. Further, the Vohs and Schooler result fits with the idea that people will behave less responsibly if they regard their actions as beyond their control. If I think that there’s no point in trying to be good, then I’m less likely to try.

Even if giving up on free will does have these deleterious effects, one might wonder how far they go. One question is whether the effects extend across the moral domain. Cheating in a psychology experiment doesn’t seem too terrible. Presumably the experiment didn’t also lead to a rash of criminal activity among those who read the anti-free will passage. Our moral revulsion at killing and hurting others is likely too strong to be dismantled by reflections about determinism. It might well turn out that other kinds of immoral behavior, like cheating in school, would be affected by the rejection of free will, however.

Is the Effect Permanent?

Another question is how long-lived the effect is. The Vohs and Schooler study suggests that immediately after people are made skeptical of free will, they cheat more. But what would happen if those people were brought back to the lab two weeks later? We might find that they would continue to be skeptical of free will but they would no longer cheat more.

There is no direct evidence on this question, but there is recent evidence on a related issue. Philosopher Hagop Sarkissian of the City Univeristy of New York and colleagues had people from Hong Kong, India, Colombia and the U.S. complete a survey on determinism and moral responsibility. Determinism was described in nontechnical terms, and participants were asked (in effect): whether our universe was a deterministic universe and whether people in a deterministic universe are morally responsible for their actions.
Across cultures, they found that most people said that our universe is not deterministic and also that people in the deterministic universe are not responsible for their actions. Although that isn’t particularly surprising—people want to believe they have free will—something pretty interesting emerges when you look at the smaller group of people who say that our universe is deterministic. Across all of the cultures, this substantial minority of free will skeptics were also much more likely to say that people are responsible even if determinism is true. One way to interpret this finding is that if you come to believe in determinism, you won’t drop your moral attitudes. Rather, you’ll simply reverse your view that determinism rules out moral responsibility.

Many philosophers and scientists reject free will and, while there has been no systematic study of the matter, there’s currently little reason to think that the philosophers and scientists who reject free will are generally less morally upright than those who believe in it. But this raises yet another puzzling question about the belief in free will. People who explicitly deny free will often continue to hold themselves responsible for their actions and feel guilty for doing wrong. Have such people managed to accommodate the rest of their attitudes to their rejection of free will? Have they adjusted their notion of guilt and responsibility so that it really doesn’t depend on the existence of free will? Or is it that when they are in the thick of things, trying to decide what to do, trying to do the right thing, they just fall back into the belief that they do have free will after all?