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Introduction: Humans or animals?

Imagine yourself walking in a forest with a rifle and a few friends. You have not had any food for days. You feel very hungry. You walk into a meadow where you see a tribe of about 30 creatures sitting and walking. The creatures look a bit like humans but their facial features appear less human-like. If these creatures were monkeys, you could use one of these monkeys as a food source. If these creatures were humans you would not dare to kill them. How do you decide whether these creatures belong to the human species or not?

You decide to observe the creatures’ behavior and go through a list of items that are supposed to be specific to humans.

Clothes. Suppose you observe no clothes. However, some tribes in sub-Saharan Africa including some Togolose and Nilo-Saharan tribes still commonly parade around fully naked. Further, hundreds of people wear no clothes at a number of beaches in Europe, Caribbean Islands, and even in the puritanical Massachusetts, USA, at Gay Head beach in Martha’s Vineyard.

Amulets. Suppose you see no amulets. However, many people do not wear amulets either. I have no necklaces, earrings, or tattoos. So the absence of amulets cannot let you identify them as animals.

Camp fire. Suppose that you can see no camp fire. However, you don’t usually sit by the fire either. Furthermore, maybe the tribe has not lit the fire yet.

Tools. The creatures are using some tools. Forty years ago scientists viewed the ability to use tools as a unique capacity of humans. But it has since been shown that primates, birds and even fish also use tools. For example, chimpanzees are well known to use tools to break nuts and hunt for termites. Chimps have to carefully prepare sticks used for termite-fishing by trimming twigs. Younger chimps learn the craft by observing older chimps use the tools. Jane Goodall and other scientists reported an extensive list of over thirty types of tools used in the wild by chimpanzees (e.g., Goodall, 1968; McGrew, 1992; Whiten, 1999). The use of tools was demonstrated in some birds and even fish. Green herons frequently lure fish by throwing an object in the water. Cichlid fish often use leaves to carry their eggs as in a child carrier.Thus, the use of tools per se does not clearly distinguish humans from animals.

A bonobo "fishing" for termites.

Hunting with the use of tools. You observe the creatures hunting with their tools. Are humans unique in their hunting? Not really. Jill Pruetz of Iowa State University in Ames and Paco Bertolani, of the University of Cambridge, UK, observed wild savanna chimpanzees in Fongoli, south-east Senegal, hunting bushbabies (small, nocturnal primates) with spears. The chimps make spears from strong sticks that they sharpen with their teeth. The average spear length is 63 centimeters (25 inches). The scientists reported that chimps forced their spears into crevices in hollow trunks and branches where bushbabies usually sleep: “The chimps used a ‘power grip’ and made multiple downward stabs – much the same way as a human might wield a dagger.” Once the bushbaby is killed, the chimp removes the bushbaby and eats the meat.

Watch the video of a hunting chimpanzee (Video 1.1) or follow through the screenshots below (adapted from the documentary “Ape Genius”, NOVA, 2008):

1. A chimpanzee is looking for a bushbaby hideout.

2. The chimp finds a stick (in this screenshot the chimp carries the stick in his mouth).

3. The chimp sharpens the stick with his teeth.

4. The chimp uses his foot to help aim the spear into the hole.

5. The chimp eats bushbaby meat.

Thus, tool use, even such complex tool use as hunting with spears, is not unique to modern humans.

Communication and speech. The creatures you are observing in this meadow produce vocalizations. Can you decide that the creatures are humans on the basis of those vocalizations? Not really. The non-human primates also “talk”. For example, when encountering a leopard, both Diana monkeys and chimpanzees give loud and conspicuous alarm calls. When a food source is located, the chimps will often vocalize with loud calls to inform other chimps that food has been found. If one chimpanzee sees a snake, it makes a low, rumbling noise, signaling the other chimpanzees to climb into nearby trees.

Vervet monkey of East Africa sound different warnings for different threats. Each warning results in a different reaction:

• A leopard warning sends vervet monkeys climbing into trees.
• An eagle warning makes them hide under bushes.
• A snake warning makes monkeys stand on their hind legs.
• A baboon warning sends monkeys rushing to areas with many trees.

Vervet monkeys of East Africa.

Parrots, of course, can reproduce a range of human speech sounds. It appears that at least sometimes they can understand the meaning of what they say. (We will talk at length about animal language later in this chapter.) It is clear that animals can communicate by vocalization. Thus the presence of vocalization cannot help you classify the creatures either.

Emotions. Chimps appear to demonstrate emotions such as joy and sadness, fear and despair, love and empathy. In addition, they also have vocalization to describe those emotions to others. Here is a phrasebook invaluable for talking to a chimp:

• Enjoying social interaction: Soft grunt
• Enjoying food: “Aaaaaa”
• Enjoyment of body contact: Lip smack
• Excitement: Pant - hoot
• Puzzlement: “Huuuu”
• Annoyance: Soft bark
• Distress: “Hoooo”
• Anger: “Waa” - bark
• Fear: “Wraaa”

There may be over 30 vocalizations and signs that express chimps’ emotions. Thus not only do chimps appear to have emotions, they also seem to be able to share their emotions with other chimps.

Culture and learning. Can animals learn by observation? Absolutely. One classic example, described by Lee Dugatkin in his book “The Imitation Factor”, is potato washing by Japanese macaques on Koshima Island (Dugatkin, 2001). In 1952, scientists began feeding sweet potatoes to the monkeys so they could watch the animals' social behavior. The potatoes were cut in pieces and tossed on the ground. Monkeys do not like to eat sand, so they were rubbing sand off the potatoes with their hands. One day, a juvenile female named Imo took her sandy potatoes to the water's edge and washed them clean. By 1958, potato washing had been adopted by 14 of 15 juveniles and 2 of 11 adults. These monkeys have all since died, but the macaques at Koshima Island continue to wash potatoes until this very day. Since the behavior was transmitted through observation rather than genetics, Dugatkin concluded that it was cultural transmission.

In another example, a group of wild dolphins living along the south Australian coast near Adelaide were able to learn to walk on their tails. In the 1980s, Billie, one of the females in the group, spent a few weeks in a dolphinarium recovering from an illness, a consequence of having been trapped in a marina lock. Billie received no training there, but may have seen other dolphins tail-walking there. After Billie’s experience, other females in the group picked up the behavior. Tail-walking is seen rarely in the wild, and the obvious conclusion is that they learned it from Billie. "This indicates that they do learn from each other, which is not a surprise really, but it does also seem that they exhibit elements of what in humans we would call 'cultural' behavior. These are things that groups develop and are passed between individuals and that come to define those groups, such as language or dancing; and it would seem that among the Port River dolphins we may have an incipient tail-walking culture," concluded Dr. Bossley, who studied the group of Australian tail-walking dolphins.

Dolphins demonstrate tail-walking in a dolphinarium.

Animals are also able to transfer newly acquired knowledge in a controlled environment. The team headed by Victoria Horner created a box that could be opened either by sliding the door or by lifting it. The team then trained one chimp to get fruit from the box by sliding the door and another chimp by lifting it. Each animal showed the technique to another generation of chimpanzees, which, in turn demonstrated it to another generation, and so on. In total, a chain of six chimpanzees exclusively lifted the door to get fruit, and a chain of five chimpanzees exclusively slid the door to get fruit. The researchers concluded that cultural learning can determine the problem solving technique used by chimpanzees.

Animals can also learn to use drugs. Look at Video 1.2 in which chimpanzee appear to enjoy smoking a cigarette.

Social behavior. Grooming is one of the most important social behaviors in chimpanzee communities. The utilitarian function of grooming is the removal of insects, pieces of debris, soil and vegetation from hair. The chimpanzee uses one hand to hold the hair back while the other hand (or lips and teeth) are used to remove the insects. Grooming is also used to relax tension and to maintain friendship. A chimpanzee may request or solicit grooming by approaching another chimpanzee and getting their attention by presenting a part of its body for grooming. It may scratch itself to indicate a grooming request. Grooming is a very important social behavior in chimps. A grooming session may be very short or it may continue for hours. Chimpanzees can also groom themselves.

Animals have many other human-like social interactions. For example, dolphins are known to care for an injured member of a group. Fish can cooperate and remove parasites from the skin of other fish. Even sex for pleasure is not a uniquely human trait. Sexual intercourse plays a major role in Bonobo (Pygmy Chimpanzee) society. Sex is being used as a greeting, a means of conflict resolution and post-conflict reconciliation. Sex is also traded by females in exchange for food. Bonobos have been observed engaging in a number of sexual activities: tongue kissing, oral sex, face-to-face genital sex (female-female, male-female, and male-male). Sexual activity is not limited to the immediate family. Bonobos do not form permanent relationships with individual partners. They also do not seem to discriminate in their sexual behavior by gender or age: sex often involves adults and children. Sex parties are not foreign to Bonobos. When Bonobos come upon a new food source, the excitement often leads to communal sex. Look at Videos 1.3 and 1.4. Keep in mind that these were not artificially programmed to make a point. Thus, we can conclude that social behavior is not unique to humans.

Living in caves. Jill Pruetz and Paco Bertolani, the scientists who reported that chimpanzees use spears to hunt bushbabies, also reported that the wild chimpanzees in Fongoli shelter in caves. The scientists reported that chimpanzees “use the shady interiors for socializing, taking siestas and picnicking.”

Humor. Video 1.5 shows a gibbon in a jungle aggravating two tiger cubs simply for the fun and joy of it. Video 1.6 shows a monkey that appear to amuse itself by grabbing a dog first by the tail and then by the leg. After watching the videos, one may conclude that a sense of humor is not unique to humans.

Laughter. Aristotle once observed that "only the human animal laughs." We now know that the differences between chimpanzee and human laughter may be the result of differences in the vocal apparatus. Chimpanzee laughter is generated by alternating inhalations and exhalations that sounds to the human ear more like panting. Scientists who observed chimpanzees in the wild report that a big smile and laughter-like panting are often associated with enjoyment and excitement. The movie “Ape Genius” by Nova (2008) shows a chimp smiling a great smile while enjoying making a splash in a puddle. Chimpanzees, gorillas, and orangutans show laughter-like vocalizations in response to physical contact, such as wrestling, play chasing, or tickling (just as human babies, chimp youngsters are ticklish). Thus, some primates may be laughing in the same way as humans, they just lack the vocal apparatus necessary to produce the sounds associated with human laughter.

A chimp smiling a great smile while enjoying making a splash in a puddle. Adapted from the movie “Ape Genius” (Nova, 2008).

Thus, after observing the creatures’ behavior for hours you were not able to identify them as humans or animals. In fact, classification of creatures into humans or animals on the basis of their behavior may not be possible at all.

Animal intelligence

Since you were not able to decide whether the creatures were humans by observing their behavior, you contemplate engaging them in a scientific experiment. What are you going to ask? Is there a test that can help you decide if the creatures are humans or animals? You may decide that humans are smarter and therefore run a series of intelligence tests. What intelligence test can separate the human mind from the mind of an animal?

Is it that humans are self-aware and animals are not? No. The standard test for self-awareness is a mirror test developed by Gordon Gallup Jr. in 1970s (e.g. Gallup, 1977). The test measures self-awareness by determining whether a subject can recognize its own image in a mirror as a reflection of itself. This is accomplished by marking the subject with a dye in a spot that is not normally visible to the subject (e.g. a spot on a forehead). When looking at its reflection in a mirror, the self-aware subject will notice the unusual spot and may attempt to touch it or rub it off. Many animals including dogs, cats and monkeys do not pass the mirror test. However, all of the great apes (chimpanzees, gorillas, orangutans, and bonobos), as well as dolphins, killer whales, elephants, and even magpie (a songbird species from the crow family; Prior, 2008) have successfully passed the mirror test (for review see Hauser, 1995).

Is it how well humans can count? No. In a study by Duke University, chimps and human subjects were briefly shown two sets of dots on a computer display and were asked to add them up. They were then shown two larger dot clusters representing two possible results. The subjects were asked to select the cluster that represents the sum. Duke University students (with many years of exposure to math) and the chimpanzees had comparable results, suggesting that primates have a similar cognitive system for basic arithmetic. Chimpanzee mathematical skills are reviewed by Marc Hauser (Hauser 2005).

Is it how good short-term memory is in humans? No. Young chimps were much better than university students in short-term memory tests devised by Dr. Matsuzawa. The test included three 5-year-old chimps and a number of human volunteers. The subjects saw nine Arabic numerals displayed on a computer screen (one through nine, left panel). The chimps had been taught to touch the numbers on the screen in the ascending order from one to nine. When they touched the first number, the other eight numbers turned into white squares (right panel). Subjects had to remember the position of each number and touch the numbers on the screen in the ascending order from memory. The results showed that the chimps, while no more accurate than the people, could do this task faster (Video 1.10A).

One chimp, Ayumu, did the best. Researchers included him and nine college students in a second test. In this test, five numbers flashed on the screen for a very short time, after which the numbers were replaced by white squares. Subjects had to remember the position of the numbers and touch the white squares in the order corresponding to ascending numbers. When the numbers were displayed for about 0.7 seconds, the chimp Ayumu and the college students were both able to correctly remember about 80% of the numbers. However, when the numbers were displayed for just 0.2 seconds, Ayumu still scored about 80%, while the best humans scored 40% (Videos 1.10C and 1.10D).

When I watched the videos, I was only able to get the first two numbers right. My result was no better than that of the Japanese students and 50% worse than that of the chimpanzee. One would assume that training could improve human performance. However, even after six months of training, three students in Dr. Matsuzawa’s experiment failed to catch up to the three young chimps. We are forced to conclude that short-term visual memory is significantly better in chimpanzees. (We will discuss the implications of this experiment for evolutionary brain development in Chapter II. We will come back to this experiment in Chapter III to explain the difference in information processing between humans and chimpanzees from the neurological perspective.)

Is it how good long-term memory is in humans? No. For example, squirrels, Clark's nutcrackers, and many other animals have phenomenal memories that encompass thousands of food cache locations, a capacity that would challenge most humans (who sometimes cannot remember where they parked their car). For example, Clark's nutcrackers normally store over 30,000 pine nuts in about 3,000 locations over an area of over 100 square kilometers, and remember where almost 70% of them were placed (Kamil, 1995).

Is it how good human hearing is? No. An elephant can detect sound from many kilometers (miles) away. A bat uses ultrasound to navigate in complete darkness. Human ears are insensitive to ultrasound and cannot detect audible sound as well as many animals can.

Is it how good human vision is? No. An owl, for example, can see well in nearly total darkness. An eagle can spot a moving rabbit from a kilometer (0.6 mile) away. Humans cannot detect a rabbit from a kilometer away and need special night vision goggles to approach the owl’s night vision capability.

Is it how developed human olfactory sense is? No. A dog can smell a bag of drugs that no customs officer can ever detect on his own. Bloodhounds, bred for tracking scents, have about 300 times the number of odor-detecting receptors in their noses as humans do.

Animals can be stronger, faster, smarter, and can work in groups. Then why are humans so successful? If it is because of our mind, then what is the property of the human mind that none of the animals have? How do we describe this property? How do we test it? What is the neurological basis of this property?

The truth is that we do not know what makes humans unique. We used to think that only humans make and use tools, but, as noted, we have since found numerous examples of animals using tools in the wild. We used to think that only humans can count, but it is obvious that chimpanzees have arithmetical skills. We used to think that only humans have an expanded vocabulary. We now know that chimpanzees and parrots can be taught to use hundreds of words meaningfully (discussed in detail below).

In this chapter we will attempt to identify a unique feature of the human mind. If we can do this, then we will be one step closer to understanding the process of hominid evolution and the emergence of Homo sapiens. We will discuss this process in Chapter II. Our ultimate goal is to understand neural processes that underlie human uniqueness. We will discuss neurological aspects of consciousness in Chapter III.