Human and ape behavior

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Humanity's physical ascent from the australopithecines and the other early hominids to present form is documented in the human fossil record, but only rudimentary assumptions on the behavioral characteristics of early humanity can be ascertained from the fossil record. Unable to directly observe the early hominids, humans look to others in the order primates to hypothesize the behaviors of their fossil ancestors. Of particular interest are the non-human Great Apes, who shared lineage with humanity more recently than any other primate. They are composed of the orangutan, gorilla, and the common and bonobo chimpanzee. The Great Apes and humans share a substantial amount of genetic material, and thus homo sapien is considered to be a member of the Great Apes as well.

Humans and the Great Apes share a number of similar behavioral characteristics that potentially shed light on the rise of intelligence in humans. These characteristics include tool using behavior, social group dynamics, capacity for language and comprehension, and levels of aggression.

Separation of humans and Great Apes

Apes and humans shared a common ancestor tens of millions of years ago, but diverged from that lineage at differing intervals. Orangutans are the furthest removed from human lineage both genetically and temporally. They are believed to have diverged from human lineage 14-16 million years ago[1]. Gorillas are next in line, having separated from human lineage 6-9 million years ago [2]. Common chimps are thought to have diverged 5-6 million years ago and bonobos at 4-6 million [3]. Humans and both species of chimpanzee share 98% of genetic makeup[3].

Although the proximity between chimps and humans is closest both temporally and genetically, gorillas and orangutans exhibit a number or behaviors that are similar to human behaviors.

Similarity to Humans

Tool Using Behavior

All of the Great Apes have been observed using tool in one way or another. The frequency and manner with which tools are used differs between each species[4]. Some apes use tools more frequently and in a more complex manner than others. For instance, modification and transportation of tools is most frequently seen primarily in common chimps. Nest building is considered tool using behavior, and is an activity performed by all of the Great Apes.

Tool use in humans is more complex than observed in apes, but fossil evidence of hominid tool use only dates back to 2.5 million years ago, roughly 3 million years after the divergence of chimps. Modern chimps are observed using a variety of organic tools such as sticks and twigs, and it is likely that if early hominids were also using similarly organic tools that they would not have preserved in the fossil record[5]. If this were the case, then evidence of hominid tool use would extend much further back into the hominid lineage.

Gorillas and bonobos use tools the least frequently of all the apes in the wild, although all apes have been observed using tools in laboratory settings[4][6]. Infrequent tool use is generally attributed to lack of necessity in apes rather than lack of intelligence. Larger apes such as gorillas and orangutans posses strong jaws and hands, and might not need to use tools to access their foods. In the case of bonobos and gorillas, their food sources are generally abundant and easily obtained, thus diminishing the need for tools to aid in efficient food gathering[7]. In orangutans, tool use may be limited because their solitary lifestyles decrease opportunities for social learning[7].

Common chimps use and manufacture tools the most frequently of all the nonhuman primates. They have been observed using sticks to fish for ants and termites, stone hammers and anvils to crack open nuts, and leaves to sponge water out of hard to reach collections. Common chimps are also the most adept at manufacturing and modifying their tools. For instance, when termite fishing, a chimp will create a tool kit of specific sticks to use for specific activities (the branches of Thomandersia hensii make particularly good ant/termite hill puncturing tools, while Sarcophrynium spp is more appropriate for fishing probes)[8]. The chimp will then strip the sticks of leaves and twigs, and will fray the ends to more efficiently catch termites. The chimp will then bring this toolkit to the fishing site, rather than relying on the sticks readily available at the site.

The advanced tool use in common chimpanzees indicates that chimps recognize causal relationships, a marker of heightened intelligence[9]. In addition, common chimp nutrition has been substantially influenced by tool using behavior, both in access to quality food (primarily protein from ant/termite fishing and nut cracking), and the efficient collection of that food. Evidence has been found showing tool use in chimps as early as 4,300 years ago [10]It is likely that hominids were also engaging in this kind of behavior to efficiently fuel their increasingly metabolically expensive brains [5].

Social Behavior and Aggression

All Great Apes are observed in fission/fusion societies, wherein members are continually leaving and joining groups. Social tolerance, especially of non-relatives, is something that is special in Apes and is not seen in most other species to the degree that it is in Apes[7].

Excepting bonobos, males are the dominant sex in Great Ape species. They are generally larger in size than females, a trait which they use both to subordinate females and to protect them from predators or other males. Gorilla males can be as much as twice the size of females. As in humans, power brings more females and mating opportunities for apes[11]. The more powerful a male is, the more a female will want to mate with him in order to protect herself and her offspring.

Since competition for females is high among apes, male rivalries are high. Males either have to rely on their strength or their bonds with other males in order to ascend in rank and achieve status[7]. Chimpanzees in particular are very adept at forming human-like political coalitions, since they cannot possibly expect to achieve or maintain power without significant cooperation on the part of other males. Without this cooperation, other coalitions of males could easily overthrow an alpha chimp regardless of his strength and size[11].

It is hypothesized that this strong bonding between male chimpanzees is the reason for the human-like genocide that groups of chimps inflict upon other groups of chimps. Chimps have been observed forming raiding parties with the sole intent of crossing into enemy territory to wreak destruction and violence upon the enemy group. They act with strategy and tact as they sum up their opponent and decide to mount an attack. When they do attack, it is generally on the weak or outnumbered. The attacks are brutal, and cannibalization is common[11]. Although it is unsure exactly why these raids take place, it is thought that the strong bonds and trusts males form within their group causes distrust and disdain for outsiders[7].

Division of labor is also present in ape societies. Males form hunting parties with the expressed purpose of predation. Females will also hunt, but it is done on an opportunistic rather than explicit level. Females are generally tasked with taking care of young[7].

Bonobos offer a stark contrast to the rest of the Great Apes due to the fact that females are generally in positions of power rather than males. This is due to the matrilineal nature of bonobos. Estrus in females is less prominent, and they mate with as many males as possible. They do this to keep males in a constant state of ignorance as to whether or not offspring belong to their lineage. Since males cannot know whether or not a child is theirs, they are more invested in the safety and protection of all females and offspring. This behavior also allows status to be tracked through females[12]. Females form strong bonds with each other to counter male aggression, and will often attack a male if he exhibits undesirable behavior or attempts to assert himself on females. Sexual dimorphism in bonobos is remarkably similar to human sexual dimorphism, with females reaching roughly 85% the size of males.

Bonobos also differ from the rest of the apes in their use of sex. They do not exclusively have sex for reproduction. They use sex to ease tension, as a social bonding tool, as a means of trade for food, to determine rank, as a sign of friendship, and for pleasure[7][11][12]. This is very similar to humans, who use sex for similar reasons. Oral sex, genital massage, and kissing are also activities witnessed in bonobos. Sezual interactions take place between males and females, females and females, and males and males. Monogamous pairs are not seen in bonobos, which is in accordance with human behavior. Prominent monogamy is observed in only 20% of human societies, primarily in hunter/gatherer and agricultural societies[13].

Bonobo groups are generally larger than other groups of apes, ranging from 11-15 in size. These groups congregate with larger groups frequently. In other apes, large congregations would cause high levels of tension and aggression, but bonobos ease the situation with sex and food sharing[11]. This is closely related to human cultural institutions such as cities and states, where many different people congregate in civility. In addition to this, bonobo society tends to be egalitarian, and sharing of food is very common. Male/female relationships are strong, and males must be accepted by higher ranking females if they are to ascend in rank[14].

Language and Communication

Apes have the intelligence for language, but in a limited fashion. Physically, their vocal apparatus is not developed enough to make the complex sounds that compose human language. Common and bonobo chimps perform very well with sign language and with symbols, and can make “declarative and evaluative statements, use symbols with each other, engage in rudimentary conversational exchanges, comprehend requests for actions involving relational terms, understand basic metacommunications about symbols and symbol performance, utilize some rule-following grammatical structures, describe baseic properties of their experience, and engage in deceptive communications.”[15] They generally have limited capabilities when communicating about things or events separated in time and space from the present. They communicate mainly about their immediate needs and desires. They have difficulties with complex grammar and complex social emotional vocabulary. Their ability to use complex communicative language is an imitated trait that does not appear in complex forms in the wild[15].

The chimp Washoe was able to learn over 100 signs of American Sign Language and communicate effectively with her human caretakers. She was able to reference things that were not immediately within her vicinity, and could communicate her thoughts and desires effectively. She would also sign to herself when looking at magazine and sometimes while performing specific actions (she signed “quiet” when she was trying to sneak into a forbidden area)[16].

Kanzi,a male bonobo, showed remarkable social awareness by understanding that other apes did not have the same training as himself and attempting to teach them. Their human caretakers gestured actions to his sister, Tamuli, that she was supposed to perform, but she did not understand. Kanzi attempted to make Tamuli understand by pantomiming the actions she was supposed to and grabbing her hand in an effort to physically make her perform the signed activities. She did not comprehend what he was trying to tell her. Kanzi showed remarkable social awareness by understanding that other apes did not have the same training as himself and attempting to teach them.[11][17]

Chimpanzees tend to do most of their learning from members of their group who are their age or older. In other words, they do not regularly observe younger group member’s behavior in with the interest of imitating it. Human tradition works very similarly, with adults teaching the young, but in human culture, the old also learn from the young, particularly in the area of technology – whereas adult chimps tend to not learn technological behavior from those younger[18].

Facial expressions and body language are also very important communication devices, as they are in humans. Human expressions, such as bearing teeth when angry, can be traced back to primitive routes wherein aggressive animals bear their teeth to display canines, despite the fact that humans no longer possess lethal canines. Both humans and the great apes express aggression through body posture, facial expression, and vocalization[19].

All of the Great Apes have a heightened ability to detect regularities in scripts (common reactions to situational stimuli), and thus are able to use this to their advantage. In other words, they have the capacity to be deceitful. This plays a large role in the social behaviors of Apes as it does in humans. One member of a group can deceive and take advantage of another based on the first member’s ability to understand the second’s natural reaction. Human deception is similar, but takes place on a much more complex scale, particularly due to language.[15]


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  2. Groves, Colin (2006) Another View of Gorilla Relationships. Gorilla Jour 62. Available: Accessed 31 March 2008
  3. 3.0 3.1 Falk, Dean (2000) Primate Diversity ISBN 0393974286
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  13. Kinsey, Warren G. (1987) A Primate Model for Human Mating Systems. . In: Kinsey, Warren G., editor. The Evolution of Human Behavior: Primate Models. Albany: State University of New York Press. pp. 105-114
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  19. Pitcairn, Thomas K. (1974) Aggression in Natural Groups of Pongids. In: Holloway, Ralph, editor. Primate Aggression, Territoriality, and Xenophobia. New York and London: Academic Press. pp 242-253