PRIMATE BEHAVIOR

PRIMATE BEHAVIOR

 

LOCOMOTION

Bonobos were first recognized as a distinct species in 1929.

Bonobo locomotion involves more hanging and leaping than that of the common chimp. Different populations vary in the percentage of time spent using bipedal/quadrupedal locomotion and the amount of time spent in trees (Wrangham, 1994).

 

 

BEHAVIOR

More than 100 different behaviors are known in chimpanzees. Although there are single behaviors which can vary between the populations of a species, such as the songs of birds, for example, no species other than humans has as many variable behaviors as chimps. About 40 different behaviors which include the use of tools, forms of play, and nonverbal communication have been shown to vary between wild chimp populations (Whiten, 1999).

 

When hair stand up on a chimpanzee, it makes them appear larger.

Reconciliation, coalitions, and reassurance are known in chimps. Females can help specific males attain dominant positions in a group (De Waal, 1982). Both chimps and orangutans recognize themselves in a mirror. Reciprocity, deception, cooperative hunting, and the instruction of infants in tool use is known in chimps (Wrangham, 1994).

 

 

TOOL USE

After Jane Goodall told Leakey that wild chimps make and use tools, he replied “Now we will have to redefine tool, redefine man, or accept chimps as man.”

Humans are not the only animals to use tools. Tool usage is especially common in chimps: sticks for termites, wad of chewed leaves to remove water from tree holes, stout sticks to dig up ant, bee, or termite nests, leafy branches for sandals or gloves, leaf cushions to protect from thorny branches, bone picks to extract bone marrow, leaf napkins to clean themselves and infants, leaves to scoop water, natural objects to carry water, and mortar and pestle to smash palms. Not all chimp populations have the same practices/tool usage-- these are passed down in each population as a learned behavior.

Chimpanzees regularly use tools in all parts of their range and in all habitats. In captivity they have created flaked stone tools. There are differences in the tool usage in different populations which some have considered to represent a primitive sort of culture (McGrew, 1992; Fouts, 1997).

A greater frequency of nut smashing has been observed in chimpanzees in far West Africa while ants compose a greater part of the chimp diet in East and Central Africa. Some populations hunt a greater percentage of adult colobus monkeys while others hunt a greater percentage of infant colobus (Wrangham, 1994).

 

With the exception of the use of shelters to protect from rain, tool usage is not as common in Bonobos as it is in common chimps. Gorillas and gibbons have also not been observed to use tools extensively, although in none of these species have the studies been as extensive as those observing common chimpanzees. In captivitiy, orangutans have learned to manipulate fire (McGrew, 1992).

 

There are gender differences in the tools used by common chimpanzees. Females spend more time extracting termites and ants and thus use these materials more frequently. Males are more likely to use sticks and stones as weapons (McGrew, 1992).

 

Chimps, gorillas, and orangutans all build nests and this behavior is not known in any other species of catarrhine primate. Gorillas build their nests on the ground while both species of chimpanzee and orangutans build tree nests. In Bonobo chimpanzees, females make their nests higher in trees and they require more time to build them (Wrangham, 1994).

 

Chimpanzees seem to utilize medicinal plants when they are sick (Wrangham, 1994).

 

 

DIET

Chimpanzees are known to eat 25 species of mammals; the 11 species of primate which are included in their known prey include human infants and cannibalism of other chimps (McGrew, 1992). Chimpanzees can kill prey which weigh up to 20 kg (45 pounds) (De Waal, 2001).

 

In determining which chimps eat meat after a kill, age and kinship are determining factors. Females in estrus receive more meat than other females (McGrew, 1992).

 

 

LANGUAGE

“Speak and I shall baptize thee.” Cardinal of Polignac said to a chimp in the 1700s. (Some families which have kept chimps have baptized them without speech.)

The brain regions required for human speech are to some degree homologous to those used for communication in monkeys (Aboitiz, 2006). Old World monkeys possess a cerebral area homologous to Broca’s area which controls orofacial muscles. Human language might have evolved through improvements in the control of ancestral communication using facial and vocal muscles (Petrides, 2005).

 

Because the human head is held upright over the spinal cord, the pharynx and oral cavity meet at almost a 90 degree angle unlike the slope present in other apes. This determines the repertoire of sounds which can be produced. The tongue and larynx are anchored lower in the neck. Although there have been attempts to teach apes to talk vocally (with a few words mastered), their tongues are too thin and the larynx too high to permit much success anatomically. Apes are also fairly quiet in the wild so this isn’t a natural behavior (Savage-Rumbaugh, 1998; Fouts, 1997). Sign language is also more difficult for non-human apes since the hands are also used for quadrupedal locomotion and not as dexterous as human hands (Savage-Rumbaugh, 1998). In 1967 Adriann Kortlandt identified the use of hand-signs in wild populations of chimps, with 3 different populations had 3 different “stop” signs (Fouts, 1997).

Chimp signs consistent with our definition of language (Bodamer, 2002; Fouts, 1997). Chimps can understand some human speech and recognize affective aspects of human speech. Sign language has been taught to gorillas, common chimpanzees, and Bonobo chimpanzees (Savage-Rumbaugh, 1998; Savage-Rumbaugh, 1986). Twenty-five hand signals are known in to occur in Bonobo sex (Bagemihl, 1999).

 

Dan Fouts has spent decades teaching chimpanzees sign language. He began with a chimp named Washoe. At 10 months Washoe combined signs “Gimme sweet”, “Come open”; and later “you me hide.” Washoe and Lucy invented new signs that they had not been taught (even when their trainers used a different set). Their toilet was called “dirty good”, the refrigerator was “open food drink”, watermelon was “candy drink” and “drink fruit”, radish was “cry hurt food”, and swan was “water bird.” Contrary to expectations, only 5% of the observed chimp conversations were about food (Fouts, 1997).

By age 5, Washoe was using 132 signs and understood hundreds of others. When tested to determine her accuracy, she received scores of 71% to 86%. The random use of signs would have produced accuracies well under 5%. Even when she was mistaken, there was the indication of understanding--she might mistake “comb” for “brush” or “nuts” for “berries” but not “comb” for “berries.” Washoe understood word order such as the difference between “me tickle you” and “you tickle me”. Washoe “read out loud” --signed to herself while reading a magazine alone and identified pictures. On seeing other chimps for the first time and asked what they were, Washoe called them “black bugs”. After getting to know one, she became “black woman”.

During her second pregnancy, when asked “what in your stomach?”, Washoe replied “baby, baby” and cradled her arms. When taking care of a 10 month old infant (to replace hers which had died), she at first said “come baby” and taught him a sign on her 8 th day with him. Washoe repeated signs over and over with him; Loulis was regularly signing to humans and chimps after 8 weeks, all signs were learned from Washoe (the humans were taking care not to sign). This was the first nonhuman to teach a human language to another nonhuman (Fouts, 1997).

The following is a sample conversation between Roger Fouts (human) and Washoe from Fout’s book Next of Kin:

R (looking at watch anxiously): You me go home now.

W: No

R: What do you want?

W: Candy

R: OK. OK. You can have candy at home.

W (very happy): You me hurry go.

 

The following passage is also taken from Next of Kin:

One of our long time volunteers, Kat Bach, once told me that when she first met Washoe she was amazed that a chimpanzee could use human language. But after getting to know the chimps, she was instead amazed by what Washoe communicated. In the summer of 1982 Kat was newly pregnant, and Washoe doted over her belly, asking about her BABY. Unfortunately, Kat had a miscarriage, and she didn’t come to the lab for several days. When she finally came back Washoe greeted her warmly but then moved away and let Kat know that she was upset that she’d been gone. Knowing that Washoe had lost two of her own children, Kat decided to tell her the truth. MY BABY DIED, Kat signed to her. Washoe looked down to the ground. Then she looked into Kat’s eyes and signed CRY, touching her cheek just below her eye. That single word CRY, Kat later said, told her more about Washoe than all of her longer, more grammatically perfect sentences. When Kat had to leave that day, Washoe wouldn’t let her go. PLEASE PERSON HUG, she signed (Fouts, 1997).

 

OTHER COMPLEX THOUGHTS

Old World monkeys can respond to symmetry, although their responses are weaker than those of humans (Sasaki, 2005).

 

Apes and humans recognize the images seen in the mirror as a reflection of self while most animals consider the reflection to be another animal. Monkeys show intermediate responses in which the reaction to mirror images was distinct from responses to unfamiliar individuals and similar to responses to familiar individuals. It is possible that capuchin monkey responses to mirror images come even closer to a recognition of self (de Waal, 2005).

 

Plato felt that only humans remembered the past and planned for the future. In Fouts’ chimp group, one begins asking for “candy tree” (Christmas tree) almost every year after Thanksgiving; one asked for “bird meat” (Thanksgiving) after Halloween. The chimp Dar had her “birthday” the day after a human researcher’s birthday, after the person’s birthday party a chimp asked “ice cream Dar?” (Fouts, 1996)

Apes are the only animals other than humans which recognize their own reflection in mirrors.

Chimps will eat certain berries only when they are sick in the wild—is this a recognition of medicinal value of certain plants? (Fouts, 1997).

Washoe once jumped an electric fence to save a human in trouble by the edge of water ( Linden, 1986).

 

ART

Chimps paint enthusiastically in captivity and title own their paintings. Washoe had a painting named “Electric Hot Red”. Tatu wouldn’t stop an unfinished painting, not even for dinner while other chimps were less inclined and might even eat the paints. Since chimps could “talk” about their paintings (using sign language), it was shown that the ability to paint representationally was shown not to be human-specific (Fouts, 1997).

 

 

ARE CHIMPS HUMAN?

Of course not. Humans are unique in many wonderful ways and no one is arguing otherwise. However, the separation between humans and other animals, particularly the apes was once perceived as some gaping chasm of qualitative differences. Now, as we better understand humans and other animals, the distance between us is nowhere near as great as was once thought.

 

 

VIOLENCE

An estimated 10% of gorilla infants are killed by an adult male gorilla who displaces another male as leader of a harem of females. The majority of males commit infanticide at least once during their lives and most females will have an infant killed by an adult male gorilla (Bagemihl, 1999; Wrangham, 1996).

 

Chimps can attack each other in lethal gang attacks. High ranking female chimps have been observed to kill low ranking females and to commit infanticide of the offspring of low-ranking females. Aggression is often displayed towards immigrant females. High-ranking females mature faster than low ranking females, perhaps because they are better nourished (De Waal, 2001).

 

Male chimpanzees are known to kill the infants of chimpanzees who belong to other groups. A few cases are known in which males killed infants in their own group if the female was a new immigrant to the group. Infanticide was not committed on the offspring of immigrant females once they had mated with the males of the group (De Waal, 2001).

 

Chimpanzees and humans are unusual among animals in that they are prone to kill individuals of their own species which belong to different social groups (De Waal, 2001). Chimpanzees understand the value of number in intergroup combat. In order to attack a solitary individual from a neighboring group, at least three males must be present. If a chimp call is played over a loudspeaker, the chimps of a group will only respond and prepare to attack if there are three or more males present (Hauser, 2005).

 

Compared to common chimpanzees, Bonobo males are less aggressive and form closer bonds with females which are not limited to the period of estrus. Unlike common chimp males, Bonobo males do not form lethal raiding parties or commit infanticide (Savage-Rumbaugh, 1998).

 

In 1974, the first case in which non-humans deliberately sought for an individual of their own species in order to attack and kill them was recorded. A group of common chimps silently passed into the territory of a neighboring group, encountered a solitary male, and beat him to death. In 1977, the members of one group of common chimps fatally assaulted the males of a neighboring group one by one over time and abducted the females until the neighboring group no longer existed (Wrangham, 1996).

 

In both orangutans and common chimpanzees, heterosexual intercourse can involve forceful coercion of the female. In orangutans, female coercion may be a factor in as many as 1/3 of matings. Once, an orangutan male raped a human woman. In common chimpanzees, females can be assaulted by males of the group which apparently results in a female being more likely to submit to the male (Wrangham, 1996).