Chimpanzees are especially interesting in that, as our closest living relatives, their behavior provides some insights into the behavior of our pre-human ancestors. I submit that it is plausible that their behavior is close to what human behavior would be were it not for human intelligence. In reality we have two close chimpanzee relatives. The one we are all familiar with is formally called Pan troglodytes and the other, the "pygmy chimpanzee," is formally called Pan paniscus. Hereafter I will use "chimpanzee" to refer to Pan troglodytes and "bonobo" to refer to Pan paniscus. I will reserve "chimp" to refer to both.
Despite having been historically referred to as a "pygmy chimpanzee," the bonobo is really only slightly smaller than the chimpanzee. However the differences between these two species involve a great deal more than just size. In particular there are striking behavioral differences that are going to complicate my efforts to isolate the foundations of human behavior.
Both chimpanzees and bonobos form social groups that have been identified as "party-gangs" by anthropologists. I will refer to them simply as "gangs." Chimpanzee gangs vary in size from just a couple individuals up to dozen or more, and their size fluctuates considerably depending upon the availability of food resources. Bonobo gangs tend to be larger and more stable, and their size does not fluctuate as much. Chimpanzees eat mostly fruit but also meat when it is available. Bonobos eat fruit, herbs and meat when it is available. The difference in diet is due to the fact that chimpanzees share their range with gorillas, and the gorillas consume the herbs. Bonobo gangs tend to be larger and more stable because their food resources are more varied and are not shared with so many other competing species. When food resources run short for chimpanzees, they leave their gang and look for better conditions elsewhere.
Chimpanzee males play very intense dominance games with each male seeking to be the dominant or alpha male of the gang. Dominance games involve raucous displays involving loud vocalization, hurled and dragged objects, posturing, physical assaults and intense political intrigues. A male may achieve alpha status simply on his own, but more often his ascent is dependent upon the support of allies. Other males are more likely to be useful to the alpha male as allies, but females constitute a significant political force in determining which male becomes alpha and how long his tenure is. Alpha status affords a male first choice of food resources, females in estrus and pretty much any material resource available to chimpanzees. The alpha male may deny other males access to females in estrus even when he himself is sated. An older female may temporarily dominate her own son, but ultimately, every male chimpanzee becomes dominant over females. This state of affairs is sustained by the facts that
Subordinate chimpanzees are required to make appropriate subservient gestures when a superior male is about, and failure to do so can result in a physical assault. This rule applies to both males and females. Although all males try to become the alpha male, the alpha males' time in that position inevitably comes to an end. A male who loses alpha status may remain within the chimpanzee gang, or he may be totally ejected depending upon how many enemies he has and how severely alienated his enemies are.
The alpha male and his allies (often relatives) are the organizational hub of the chimpanzee gang. Even when times are bad the alpha male and his allies remain together in the same geographical area. Each gang controls a geographic area, which is to say that de facto, the alpha male and his allies own the geographic area. They defend their territory from encroachment and seek to encroach upon surrounding territories. Encroachment involves periodic stealthy forays into surrounding territory for the purpose of isolating and killing an individual from another gang. Usually it is males who are the victims of these forays, although occasionally a female may be killed. Sometimes females will accompany males on a foray. A female has a much better chance of being accepted into a foreign gang than does a stray male. This piecemeal predation can result in one chimp gang exterminating another over a period of time. This predation is very dependent upon opportunity, in that chimps only attack when the odds are many to one. Thus massed confrontations between chimpanzee gangs do not occur.
Chimpanzee males organize hunts for meat with the most common prey being monkeys. Sometimes females will accompany males in hunts, but in the end the alpha male becomes the owner of the meat and, he typically will hand out portions to favored members of his gang. Males who provide meat are greatly favored by females.
This discussion of violence among chimpanzees is a discussion of anomalies. Even the alpha male spends most of his time relaxing, browsing for food, sleeping and grooming other chimps... including his rivals for the alpha male position.
Among bonobos, the institution of the alpha male exists in that there is one, and he can often impose his will on any other individual member of the gang. However, his power is much more limited than that of his chimpanzee counterpart in that bonobo females ally themselves with each other and as a group can impose their will on the alpha male. Bonobo females control food resources, and males may have to scavenge to get by. Also females will gang up and physically assault a male who is too aggressive. Indeed, the most violent assaults among bonobos occur within the gang and are carried out by females against males. All this is made possible by the generally greater availability of food resources for bonobos. Bonobo gangs are larger and much more stable than chimpanzee gangs. Bonobo females have an opportunity to form alliances that is generally not available to chimpanzee females. Then, too, bonobo males have a generally less aggressive demeanor than chimpanzee males.
Although bonobo gangs control a piece of territory, they do not have the intense confrontational attitude towards neighboring gangs that chimpanzees have. So far as I can tell, there is no documented evidence of bonobos killing members of neighboring gangs. Meetings between gangs start out tense but often turn into social occasions involving copulation.
Bonobos hunt and consume meat, but I have found relatively little documentation of this behavior as compared to that of chimpanzees.
Chimp females devote a lot of time and energy to caring for their young. In fact, it is fair to say that this is their primary occupation. Chimp children, like most mammals, are born in a state of near helplessness. Without the care that female chimps lavish upon their children, chimps literally would not exist. This care involves not just simply supplying food but also in tending to the psychological needs of young chimps. Females teach their adolescent daughters how to care for children by at first allowing them to briefly care for a youngster and then progressively shifting more and more parental burdens onto the adolescent daughter. By the time a female chimp reaches her first estrus, she has a lot of experience in tending to children. This training is critical; female chimps are not born with the knowledge of how to care for children.
Female chimpanzees are dominated by male chimpanzees. They not only acquiesce in these circumstances but seem to actively promote them. Females tend to find the alpha male to be the most attractive sexual partner. They rely upon the alpha male to protect them from excess violence from other males of the gang. In effect, the alpha male is the policeman or government of the gang. They rely on all males to deal with predators operating from outside the gang, and that includes chimpanzees from other gangs as well as predators from other species. If they are together long enough in a stable gang, female chimpanzees will develop friendships and alliances. This can make them into a potent political force and give them major influence in determining who the alpha male is. Females have been known to support one male in an alpha male dispute by engaging in coordinated physical violence against his opponent.
Female chimps are eager to get meat to eat. For them meat is a concentrated dose of nutrients that can be had elsewhere, but only at the cost of considerable time and effort.
Female chimpanzees have been known to go on a rampage and kill children that are not their own, although this form of behavior is relatively rare. Female chimpanzees have also been known to briefly leave a gang and engage in sexual liaisons with males of a neighboring gang.
Chimpanzee males and females only have a sexual interest when the females are in estrus. During this time the female genitalia swell and change color. Chimpanzee males can easily tell when a female is receptive and male dominance relationships usually determine which male chimpanzees get to mate. The alpha male especially tends to become agitated at the sight of a female in estrus mating with another male. He may acquiesce in the situation depending upon the political status of the other male and especially if the other male is a political ally. Despite all this, no male is ever completely excluded from sexual relations with females because sooner or later the alpha male has to sleep, and he can never be everywhere at once.
Female bonobos give no external indications of when they are in estrus. Bonobos engage in sexual relations on a more-or-less continuous basis without much significance being placed on the sex of the partner. Male dominance relationships in bonobos have little or no influence on bonobo sexual practices. Bonobos can be accurately described as a thoroughly hedonistic bisexual species, whereas chimps are a conspicuously patriarchal and consistently heterosexual species.
Within the gang and beyond just the alpha male, chimpanzees set up a social hierarchy that involves every member of the gang regardless of sex. A chimpanzee with a higher status gets first choice of available resources vis-a-vis a chimpanzee with lower status. Also chimpanzees with higher status tend to be preferred sexual partners. Chimpanzees spend a lot of time grooming each other, and grooming is done on a more-or-less non preferential basis. It serves to knit together a social organization that is stressed by the hierarchy system.
Likewise bonobos have a social hierarchy system, but females play a much different role in it. The alpha male is usually the son of the alpha female. It would probably be more accurate to say that bonobo society is headed by an alpha female than by an alpha male. Although the alpha female is not more physically powerful than the alpha male, she has allies that will back her up in a physical confrontation whereas the male does not.
Chimpanzees select and use tools. This can involve picking up a convenient stick and lobbing it ,or it may involve the careful selection of a twig with just the right properties so that it can be used to tease termites out of a mound. This use of tools is invented behavior. Chimpanzees in widely separated geographic areas will use different tools. This is to say that they will know the use of some tools but not of others.
To the best of my ability, this summary is an accurate reflection of chimpanzee and bonobo behavior. I have had considerable difficulty in isolating the real behavior of these species. From the reading I have done it is obvious that many researchers are afflicted with one degree or another of "political correctness." Bonobos are politically correct; chimpanzees are not.