The hidden factor / Gary Stix

The ability to take part in communal tasks such as hunting large animals and building cities may be what separated modern humans from our primate cousins 

In a psychology laboratory in Leipzig, Germany, two toddlers look at gummy candies placed on a board beyond their reach. To get to the candy, the two toddlers have to pull together two ends of a rope. If only one child pulls, the rope will be released and they will get nothing.

A few kilometers away, in Pongoland, the living facility for great apes at the Leipzig Zoo, the researchers are repeating the same experiment in a closed and transparent enclosure and this time with two chimpanzees. If the primates pass the board and rope test, they each get a fruit.

Through such tests of children and chimpanzees, researchers hope to solve a vexing puzzle: Why are humans such a successful biological species? Homo sapiens (the person) andPan Trogolodites (The chimpanzee) share almost 99% of their genetic material. Why, then, did humans manage to populate almost every corner of the planet, build the Eiffel Tower, create Boeing 747 airplanes and hydrogen bombs? And why do chimpanzees still forage for food for their daily meal in the tangled forests of equatorial Africa, just as their ancestors did seven or eight million years ago, when primitive humans and great apes separated into different biological species?

As with any event that has occurred on the time scale of evolution, spanning hundreds, thousands, or millions of years, scientists may never agree on what really happened. For many years, the dominant view was that only humans make tools and use them, and only they are capable of logical thinking with the help of numbers and other symbols. But this opinion was abandoned when we learned what other primates are capable of. A chimpanzee that learns from a suitable trainer, can perform connection operations, operate a computer and light a cigarette.

The question of why the behavior of humans is different from that of apes, and to what extent it is different, is still controversial today. Experiments such as the one conducted in Leipzig under the auspices of the Max Planck Institute for Evolutionary Anthropology raise the fascinating possibility of identifying an aspect of the human cognitive mechanism, which may be unique, although difficult to distinguish. Starting at the age of a little less than a year, a milestone that some psychologists call "the nine-month revolution", children begin to show a clear awareness of what is going on in their parents' heads. This new ability is manifested in the fact that they follow their parents' gaze or look in the direction the parents are pointing. Even chimpanzees can decipher to some extent what is going through the mind of someone close to them, but humans go one step further: a child and an adult can also think together and focus on what needs to be done to carry out a joint task. The simple act of a child and an adult rolling a ball at each other is possible thanks to this seemingly modest cognitive advantage.

Some psychologists and anthropologists believe that this melding of minds was a crucial turning point that occurred hundreds of thousands of years ago and shaped the later evolution of man. The ability of small hunter-gatherer groups to work together in harmony led over time to a flurry of cognitive changes that in turn led to the development of language and the spread of diverse human cultures on Earth.

This account of human psychological evolution, assembled from bits and pieces of studies on children and chimpanzees, is speculative and has been questioned by some. But it provides a picture that is probably the most comprehensive and impressive of the origins of the cognitive skills that make humans special.

The cogwheel effect

The Max Planck Institute has the largest research facility in the world specialized for examining the differences in behavior between humans and great apes. Dozens of studies may be conducted in it at any given moment. The researchers can find subjects from a database of more than 20,000 children and recruit chimpanzees or individuals from any other species of apes, orangutans, bonobos and gorillas from the Wolfgang Keller Primate Research Center at the Leipzig Zoo located a few kilometers away.

The institute was established 17 years ago, seven years after the reunification of Germany. The establishment of the institute required the founders to deal with the tainted legacy of German anthropology, with its link to Nazi racial theories, and above all, with the horrific human experiments conducted in Auschwitz by Josef Mengele, a doctor who held a doctorate in anthropology. The organizers of the institute made an extraordinary effort to recruit to its ranks heads of research groups who were not German, in the fields of genetics, primatology, language, and other fields of thought.

One of them was Michael Tomasello, a tall and bearded psychologist and primatologist. Michael, who is now 64 years old, grew up in a small town of citrus growers in the central peninsula of Florida. He began his academic career at the University of Georgia, writing a dissertation on how toddlers acquire language. When he was working on his doctorate in the 70s, linguists and psychologists used to point to language as the first and foremost exhibit that highlights the uniqueness of humans in the animal world.

Tomslow's thesis documented how his almost two-year-old daughter acquired her first verbs. The appearance of pre-words, such as "play play" or "ni ni", revealed a natural tendency of a small child to experiment with testing language components by way of trial and error, an exercise that gradually became a more accepted construction of grammar and syntax. This learning process was contrary to the ideas of Noam Chomsky and other linguists who claimed that grammar is somehow genetically anchored in our brains, an explanation that Tomaslo thought was too simplistic. According to him "Language is such a complicated thing that it cannot have evolved like the thumb in the palm of the hand that stands against the other fingers."

His research on language expanded his thinking about the relationship between culture and human evolution. Tomslow came to the realization that forces of selection on their own, acting on physical traits, cannot explain the appearance of complex tools, of language, of mathematics, and of complicated social institutions in the relatively short period of time across the evolutionary timeline since the branches of man and chimpanzee separated from each other. Some kind of innate mental capacity shown by hominins (modern humans and our extinct relatives), but absent from non-human primates must have been behind our ancestors' ability to behave in ways that enormously accelerated their ability to feed and clothe themselves and thrive in any living environment, however harsh.

When Tomslow moved on to become a professor at Emory University in the 80s, he enjoyed access to the Yerkes Center for Primate Research, where he could look for clues to the existence of this ability in studies that compared the behavior of children to that of chimpanzees. The transition sent him on a decades-long research journey, which he continued at the Max Planck Institute, since 1998.

In his studies of chimpanzee learning, Tomslow noticed that great apes do not imitate each other in the same way as humans. One chimpanzee may imitate another and use a stick to dislodge ants from a nest. Others in the group may follow suit. When Tomslow followed them closely and over time, he got the impression that the chimpanzees could understand that a stick could be used to "collect ants", but they showed no interest in imitating other techniques that might be used to hunt insects. And what's more important than that: there was no attempt to go beyond the basic operation, to keep fiddling with the stick to create a new and improved ant catcher.

In human societies, on the other hand, this kind of innovation is a characteristic feature that Tomslow calls the "ratchet effect". Humans modify and renovate their tools to make them better and pass this knowledge on to their descendants, who in turn add their own renovations and the rolling improvements upgrade the gears. What begins as a high-bump stone slingshot invented to kill a mammoth evolves over the generations into a rocket launcher, rock-dissolving catapults, a rifle ball, and finally an intercontinental ballistic missile.

This cultural cogwheel provides an explanation, in a rough approximation, of the question of man's success as a biological species, but raises another question: What specific mental processes are involved in the transmission of such knowledge to others? The answer should begin with guesses about changes in the physiology and behavior of the hominins that may have occurred hundreds of thousands of years ago. One idea, the social brain hypothesis formulated by Oxford University anthropologist Robin Dunbar, holds that group size, and hence cultural complexity, increases in size as the brain gets larger. And scientists know that already 400,000 years ago, Homo heidelbergensis, probably our direct ancestor, had a brain almost as big as ours.

Tomslow states that early hominins, equipped with larger brains and faced with the need to feed a growing population, began to take careful planning steps to track and outsmart animals. The circumstances of life exerted strong selection pressures that encouraged cooperation: any member of the group of hunters who was not able to act as a team and assume a defined role when following the animal and confronting you, was not included in the following hunting trips and his future was extremely bleak. If one hunter was a bad partner, Tomslow says, the rest of the group would decide: "We're not going to do it again." In his opinion, what separated modern humans from the hominin band was an evolutionary adaptation in the direction of over-sociality.

The paleoarchaeological record of the bones and man-made objects is scant to provide support for Tomslow's hypothesis. He draws his evidence from comparisons between a child and a chimpanzee: he compares the closest primate to us with a toddler who has not yet acquired language and has not been exposed to formal education. The unguided child allows researchers to gauge the cognitive skills that have not yet been formed or shaped by social influences, so they can be seen as innate skills.

The research in Leipzig over the past decade has revealed more similarities than differences between humans and chimpanzees, but they also highlight what Tomslow calls "a small difference that makes a big difference." One research project, large in scope, led by Ester Herman from the Department of Developmental and Comparative Psychology at the Max Planck Institute, and directed by Tomslow, was conducted from 2003 until the publication of its findings in the journal Science in 2007. It involved conducting multiple cognitive tests for 106 chimpanzees in two African nature reserves, 32 orangutans in Indonesia and 105 two-and-a-half-year-old toddlers in Leipzig.

The researchers set out to determine whether the larger brains of humans meant that children would be smarter than the great apes, and if so, what exactly being smarter meant. The three biological species were tested for their capacity for spatial understanding (eg, searching for a hidden prize), ability to distinguish between larger and smaller quantities, and understanding of cause-effect relationships. It turned out that the toddlers and the chimpanzees scored almost identically on these tests (the orangutans did less well).

But when the tests were in the area of ​​social skills, there was no room for comparison at all. The toddlers scored the best, outperforming both the chimpanzees and the orangutans on tests (adapted to the nonverbal great apes) that tested the ability to communicate, learn from others, and evaluate someone else's perceptions and desires. The researchers interpreted the results as indicating that humans are not born with a higher IQ (general thinking skills), but are instead equipped from birth with a special series of abilities, which the researchers called in an article in Science called "cultural intelligence", which prepares them to learn from their parents, teachers and game partners. "This was actually the first time we found that social cognitive abilities are crucial skills that make us special compared to other animals," says Herman.

Further deepening must penetrate to the depth of the unique psychological processes that are at the foundation of the ultrasocial tendencies of humans. Tomslow's research showed that around nine months of age, parent and child cooperate in something that can be thought of as mind reading. Each of them has what psychologists call a "theory of the mind". Each is aware of what the other knows when they look together at a ball or game brick and play a little game with them. Each holds a mental image of these objects in the same way that a group of Heidelberg men would imagine the sight of a stag destined for dinner. This ability to act in cooperation with another person to play or achieve a common goal is what Tomslow calls joint intentionality (a term borrowed from philosophy). According to Tomslow's view, shared intentionality is an evolutionary adaptation unique to humans. This is a subtle difference whose results are significant, anchored in a hereditary tendency to reciprocal relations of social sharing to an extent not found in chimpanzees or any other species.

The benefits of reading minds

The institute's researchers noticed that the chimpanzees are also able to a certain extent to read one another's mind. But their natural tendency is to use what they learn in this way to outdo each other in the race for food or mates. The chimpanzee's mind, it seems, is immersed in Machiavellian-style mental intrigue: "If I do this, what will he do?", as Tomslow explains it. "It is inconceivable," he said in an October 2010 lecture at the University of Virginia, "that you would ever see two chimpanzees carrying a log together." The Leipzig researchers formally demonstrated the differences between the two biological species in the rope and board experiment, in which two chimpanzees at the Leipzig Zoo could only get a fruit snack if they both pulled together the rope connected to the board. When the food was placed at both ends of the board, the monkeys took the dish closest to them. But when the treats were placed in the middle, the more dominant monkey grabbed it, and after a few tries, the dominant monkey just stopped playing. In the children's laboratory at the institute, the children worked together, whether the candies were in the middle or at the ends of the board. When the candy was placed in the middle of the board, the three boys negotiated and shared the loot equally.

Early humans' mutual understanding of what was required to accomplish a task laid the foundations for the beginnings of social interactions and a culture based on cooperation, Tomslow argues. It is possible that the "common base" as he calls it, within the framework of which members of the group know most of what is known to others, is what paved the way for the development of new forms of communication.

The ability to conceive common goals and notice their existence, and to understand with immediate intuition what a hunting partner is thinking, probably allowed our hominin ancestors to take great cognitive steps in other directions, such as the development of greater sophistication in the communicative uses of gestures, which surpasses what is available to our ape relatives.

The basic range of gestures of our hominin relatives may have been similar in the past to that of great apes. Ancient humans may have used to point with their fingers, as chimpanzees do today, to give instructions such as "give me this" or "do this", a form of communication focused on the needs of the individual. The chimpanzees, who are not yet trying to use these gestures to teach or convey information, may be reminiscent of humans in their ancient past.

For humans, gestures took on new meaning as their mental processing abilities improved. A hunter might point to a clearing to mark a place where a moose is grazing, an action that his friend who was next to him immediately understood. The way in which such a vote may take on a new meaning is clearly expressed in modern life. "If I'm pointing to indicate 'let's stop there for coffee,' that's not being said in the language," Tomslow says. "The meaning of 'in this cafe' is in the finger, not in the tongue."

Young children understand this gesture of pointing, while chimpanzees do not. This difference stands out in a study where the experimenter repeatedly placed play bricks on a plate, which a girl needed to build a tower, and she used them. At a certain point in time, there were no items left that the toddler needed, and she started pointing at the empty plate to indicate that she wanted her son who was no longer there. The girl knew that the adult would press the right button. The ability to refer to an absent entity, a unique feature that defines human language, was used here. In the zoo, the chimpanzees who experienced a similar exercise, with food instead of play bricks, did not lift a finger when faced with an empty plate.

Older children only slightly begin to understand gestures that show an action in pantomime: bringing the hand to the mouth to indicate hunger or thirst, for example. The chimpanzees who see these gestures during the study have no idea what they mean. An ape can understand what happens when a person holds a hammer and hits a nut to get its contents out, but has no idea what happens when that same person demonstrates a striking motion with the palm of his hand to convey the idea of ​​doing the same action.

This type of gesture, the expansion of man's cognitive capacity for common intent, may have been the basis for the exchange of abstract ideas necessary for the establishment of more complex social groups, whether it is a tribe or a nation. The ability to mime probably allowed people to create stories such as conveying the message "The antelope grazes over the hill", by holding both hands above the head in a V shape to indicate the animal and then raising and lowering the hands to describe the hill. These scripts are taken from comparative experiments that showed that toddlers have an intuitive understanding of iconic gestures that mark many familiar actions, while chimpanzees lack such understanding.

Some of these gestures may have been shown not only by moving the hands but also by making sounds intended to represent certain objects or actions. These guttural sounds may have evolved into speech, increasing the ability to maintain complex social relationships as populations grew and rivalries arose between tribal groups. A group that was adept at teamwork would prevail over groups that bickered.

The ever-expanding cognitive skills of humans may have promoted unique ways of doing things for hunting, fishing, gathering plants, or marriage, which later became social conventions, in terms of "our" custom, that the entire group was supposed to adopt. A collection of social conventions required each individual to acquire an awareness of the values ​​shared by the group, "group-awareness" in which each member behaved according to what was expected of him. Social norms gave birth to a set of moral principles that over time laid the foundations for institutional frameworks, such as governments, armies, legal systems and religious systems, designed to enforce the rules that people lived by. A certain way of thinking that was necessary for hunting bands was upgraded over the generations to a way of thinking suitable for entire human societies.

Chimpanzees and other great apes have never taken this particular route. When chimpanzees go out together to hunt colobus monkeys in Côte d'Ivoire, this activity, as Tomselo interprets it, involves each chimpanzee trying to be the first to catch the hunted monkey in order to get as much meat as possible, whereas human hunter-gatherers, making sure to cooperate when following the prey, and divide the spoils equally even in our time. Tomslow concludes that societies of great apes and societies of other hunters such as lions appear to be cooperative, but the forces at work in intragroup dynamics are fundamentally competitive.

The big debate

Tomslow's version of the history of evolution is not universally accepted, not even within the Institute. On the floor above his office, in the department of primatology, Kathryn Crockford talks to me from a video taken by her research student, Liran Samuni, in March 2014. In the video, a young chimpanzee is seen in the Thai National Park on the Ivory Coast, near the border with Liberia.

The chimpanzee called Shogun by researchers has just captured a large black and white colobus monkey. Shogun struggles to eat his prey, which is still alive and squirming, and he utters a series of sharp "recruiting screams" to call for help two older hunters sitting in the forest canopy above him. Kuba, one of the two, quickly arrives in the ring and Shogun calms down a bit and takes the first bite. But then Shogun continues to scream until the other hunter, Ibrahim, pulls up. Shogun, the younger chimpanzee, puts his finger in Ibrahim's mouth in a "reassuring gesture", a customary gesture assuring that everything is fine. Ibrahim provides the requested emotional support by not biting Shogun's finger. Then all three share the meal. "It's interesting that he recruits these two dominant males who were capable of taking the whole monkey from him," says Crockford, "but as you can see, they don't take his prey from him. He is allowed to eat from it."

Crockford claims that it is too early to draw conclusions about the degree of cooperation between chimpanzees. "I don't think we know what limits the chimpanzees' abilities have," she says. "I think [Tomslow's] arguments are brilliant and very clear in terms of our current knowledge, but I think with the help of the new tools we bring to the field, we will find out whether the current limits we know are the limits of chimpanzees' ability, or not." Crockford is working with several other researchers in order to develop tests that will detect the presence of the hormone oxytocin, which contributes to the creation of social bonds, in the chimpanzees' urine. Some studies have shown that the level of the hormone increases when the chimpanzees share food, a sign that they may be cooperating when eating.

Crockford did her doctoral research at the Leipzig Institute, with Tomslow and Christoph Busch, head of the department of primatology at the Max Planck Institute. Bush challenged Tomslow's conclusions by citing his extensive research in Thai National Park, which showed that chimpanzees maintain a highly cooperative social structure: one chimpanzee drives the prey in the desired direction; The others block his path or fulfill other roles. Bush's views on chimpanzee cooperation are similar to those of Frans de Waal of the Yerkes Primate Research Center at Emory University [see “One for All” on page 68]. And there are those who criticize Tomselo from a completely opposite point of view. Daniel Povinelli of the University of Louisiana at Lafayette believes that Tomslow is mistaken in overestimating the cognitive abilities of the chimpanzees when he attributes to them an ability to understand the psychological state of others in the group.

Tomslow enjoys the academic duel it provokes, and says: "In my opinion, Bush and De Waal are guilty of anthropomorphizing the apes, while Finely treats them as rats, but they are neither rats nor humans." He jokes, “We're stuck right in the middle. Since we are being attacked from both directions, we are probably right."

The condemnation coming from some places is balanced by great respect from others. "For a long time I thought that humans were very similar to chimpanzees," says Jonathan Haight, a leading social scientist at New York University's Stern School of Business. "Over the years, and largely thanks to Tomslo's work, I have become convinced that the small difference that he researches and publishes articles about, the unique human capacity for common intention, has moved us to new shores across the river, where social life is radically different."

Resolving these controversies requires further research in the zoo, laboratory and field. Perhaps the solution will come from new work examining the extent to which chimpanzees have a "theory of mind" regarding others. Another study that has already started and is being carried out by Tomslo's group aims to find out if the conclusions about human behavior, which derive from tests of the German children, are also valid for children in Africa and Asia who will be tested in the same way. One study examines whether the collective sense of good and bad that German preschoolers exhibit is also present in Samburu children, a semi-nomadic people from northern Kenya.

There is room to add and deepen the examination of the differences between humans and apes. One of Tomslow's close old colleagues, Joseph Kohl, who heads the Wolfgang Keller Center, believes that shared intention alone is not enough to explain what makes a person special. Other cognitive abilities, he says, may also distinguish humans from other primates, for example the possibility of "mental time travel": our ability to imagine what might happen in the future.

Additional perspectives regarding the degree of overlap between humans and chimpanzees may come from observing the human brain, as another study is being conducted on another floor at the Max Planck Institute. Svante Pääbo, who headed a team that completed the initial sequencing of the Neanderthal human genome in 2010, hypothesizes in a recently published book that it may be possible to test Tomslo's ideas about the uniqueness of human thinking through genetic analysis.

As these studies begin, it would make sense to begin by merging the studies of chimpanzee and human behavior with the Don Quixote quest to decipher the interactions between the hundreds of genes involved in autism. Children who have an autistic disorder have difficulty, somewhat like chimpanzees, in understanding social cues. A comparison between the genes of children with autism and the genes of children without the disorder, and then between them and the DNA of chimpanzees and perhaps also of Neanderthals, our closest evolutionary cousins, may yield a better understanding of the genetic basis of human sociability.

Such studies may also explain why, over the course of thousands of years, we have progressed from bands of wandering foragers to societies that not only provide food and shelter more efficiently than chimpanzees, but also invite countless opportunities for social contact: chances to reach every corner of the world in one day or transfer Texting Arizona or Timbuktu as fast as a thought comes to mind.

Gary Stix is ​​a senior editor at Scientific American.

in brief

In the past it was believed that humans differed from other animals in their use of tools and the general superiority of their range of cognitive abilities. Careful observations of the behavior of chimpanzees and other apes have proven these ideas wrong.

Chimpanzees score as well as small children on tests of general reasoning ability, but lack many social skills found naturally in their human cousins. Unlike humans, chimpanzees do not cooperate in the large groups required to form complex societies.

A comparison between the psychology of chimpanzees and the psychology of humans reveals that an important source of the differences between them and humans may be found in the evolution of the ability to intuitively understand what another person is thinking, so that two can work together for a common goal.

More on the subject

Cultural Origins of Human Cognition. Michael Tomasello. Harvard University Press, 1999.

Humans Have Evolved Specialized Skills of Social Cognition: The Cultural Intelligence Hypothesis. Esther Herrmann, Josep Call, María Victoria Hernández-Lloreda, Brian Hare and Michael Tomasello in Science, Vol. 317, pages 1360-1366; September 7, 2007.

A Natural History of Human Thinking. Michael Tomasello. Harvard University Press, 2014.

Dawn Modern thinking, Kate Wong, Scientific American Israel, October-November 2005.

 

The article was published with the permission of Scientific American Israel

More of the topic in Hayadan:

 

• Why are animals so smart?
• Prejudice in humans has ancient evolutionary roots