The Human-Chimp Connection

By:  Ben Ross

 

            As humans, our closest living relatives are the chimpanzees.  Chimps and humans  share 99 percent of their DNA, and are closer related to each other than they are to any other living primates.  Chimpanzees belong to the anthropoid ape family Pongidae, and make up the genus Pan, which includes chimps, Pan Troglodytes and bonobos, Pan paniscus.  Chimpanzees are divided into three subspecies--the common, or masked chimpanzee; the tschego; and the eastern, or long-haired chimpanzee.  (Rumbaugh 471)

            Structurally, chimpanzees are similar to gorillas, although they are considerably smaller.  Their upper-bodies are shaped alike, and they have corresponding limb proportions which allow them both to be efficient knuckle-walkers.  In addition to knuckle-walking, some chimps, especially juveniles, brachiate in the trees.  On the ground, chimps will occasionally walk bipedally for short distances while carrying food or other objects.  (Jurmain et al.  230-231)

            While chimps are closely related to orangutans and gorillas, there are many differences between them.  Chimps are smaller, and less sexually dimorphic than the other great apes.  Unlike the other great apes, chimps are not calm and placid.  Instead they are easily excited, and often loud and rambunctious.  In the wild, they spend fifty to seventy five percent of the day in the trees, but make frequent visits to the ground to collect food.  (Rumbaugh 472)  They are found in equatorial Africa, but their habitat is rapidly being destroyed by human advancement.   

            Like the orangutans and gorillas, chimps live in groups with often as many as fifty individuals.  The core of each community is a group of males who defend the group’s territory.  Each individual chimp possess a rank within their group.  Their rank can be determined by many factors including childhood games, and who their mother is.  The highest ranking chimp in a group is referred to as the alpha male.  The alpha male acts as the group’s leader. 

            When captive, chimps maintain many of the same behaviors they have in the wild, and live within the same social structure as do wild chimps.  When I observed the chimps at the Kansas City Zoo, my focal chimp was Jimmy, the alpha male.  It would not take long for an observer who was unfamiliar with the family to determine that Jimmy is the alpha male.  After watching him for a combined three hours, I noticed several recurring behavioral patterns.

            As the leader of the community, Jimmy must protect the rest of the community from outsiders, which in this case are people.  Unlike most of the other chimps, Jimmy shows a great interest in people.  He spends a good amount of his time with his face pressed up to the glass, gazing at the people where he frequently mimics their facial expressions.  However, when he encounters a large group of people, or a stocky, adult man he views it as a threat to the community, and easily becomes intimidated.  To show that the area is his territory, Jimmy will usually find one of the females and mate with her in front of the glass.  On one occasion when he was intimidated, Jimmy jumped up and

down, screaming at the top of his lungs, and then lunged his body at the glass with enough force to make it shake. 

            Protecting the community from the threat of outsiders is not the alpha male’s only responsibility.  He also oversees the individuals within the community to ensure their well-being.  When Jimmy is not interacting with people, he is often looking over the other chimps.  On one occasion, three of the juveniles were playing in a tall tree.  Instead of joining them, Jimmy remained at the bottom of the tree, watching the young until they returned to the ground.

            While much of the same behavior would occur in the wild, certain behavioral patterns are more pronounced in captive chimp communities.  Chimps in the wild often live in communities of up to fifty individuals.  Although there is still one alpha male, a core of bonded adult males shares many of the responsibilities that the alpha male would take on.  Obviously this is not the case in zoos because most captive communities are not this large.  Captive chimps also mate year round, and more frequently than wild chimps who typically mate from August to November.  (Rumbaugh 473)  For the most part this trait is attributed to boredom in captivity.

            By studying chimpanzees, we can gain a glimpse into our own ancient past.  For years it was believed that what separated humans from animals was our ability to manufacture and use tools.  As further studies were done on chimps, it was discovered that chimps are also sophisticated tool users.  They use specialized sticks to collect termites from holes, stones to crack open nuts, and leaves as sponges for soaking up

drinking water.  At first glance, these techniques appear to be quite simple and primitive, but they actually take a good deal of skill to master.  The use of tools is a unique skill that only exists among humans and chimpanzees.   

            Based on genetic information and behavioral similarities, humans are closer related to chimps than any other living species.  With the exception of only one amino acid, humans and chimps share an identical series of 146 amino acids comprising the hemoglobin beta chain.  Another similarity is exposed within karyotype comparisons.  Humans have 46 chromosomes.  Chimps have 48.  However, the banding patterns of human chromosome 2 correspond to those of two smaller chimp chromosomes.  Some scientists believe that in an ancestral hominid these two chromosomes fused to produce what became human chromosome 2. 

            Chimps’ and humans’ genetic and behavioral similarities indicate that they most likely shared a common ancestor millions of years ago.  The actual date of the split between hominids and pongids split is in dispute among the scientific world, but it is believed to have occurred during the Miocene period The traits that separate hominids from pongids and other anthropoids are the use of bipedality as the primary form of locomotion, smaller proportionate jaw and teeth size, and large brains.  When distinguishing hominids it must be realized that these characteristics did not all develop simultaneously.  In fact, they have been evolving for over 5 million years.

            The earliest hominid is believed to be the Australopithecus Ramidus.  Found in Aramis, Ethiopia, and dated to approximately 4.4 million years ago, A. Ramidus may be

an intermediate link between chimpanzees and early hominids such as Australopithecus Afarensis.  A. Ramidus lived in a forest environment, may have been developing bipedality, and was probably the only hominid alive at the time. While A. Ramidus was a hominid, it was very ape-like and is the closest fossil find to date to the common ancestor between chimps and humans.  (Brewington 1)  It had fairly large canines, with the upper one shearing against a cutting surface on the lower first premolar.  This sectorial tooth, as it is referred to, is found today in modern apes.  The only cranial remains discovered have been very fragmented and incomplete, so the actual cranial capacity has yet to be determined, but it is believed to be quite small.  What makes A. Ramidus a hominid is the skeletal evidence that indicates bipedality.  The foremen magnum is positioned further forward than it is in quadrupeds.  Features of the humorous indicate that the forelimb was probably not weight-bearing.  And the morphology of the pelvis is consistent bipedality.  Because of these morphological traits, many paleoanthropologists believe that A. Ramidus was fully bipedal.  Currently, a 40 percent complete skeleton is being excavated from the site at Aramis.  Once it is fully excavated and studied, this conclusion will finally be proven of falsified.  If A. Ramidus is found to have been bipedal, it will be the earliest known example of bipedality.  (Jurmain et al. 363)

            With remains found in Kanapoi and Allia Bay, the Australopithecus Anamensis is believed to be a close relative to A. Ramidus.  Although the A. Anamensis fossil collection consists only of numerous teeth, six jaws, a humorous, a radius, and part of a tibia, researchers have determined that A. Anamensis was most likely bipedal.  It had

primitive teeth and an external ear opening which was different from those seen in later hominids.  What separates it from A. Ramidus is, like other Australopithecines, it had thick enamel on its molars.  (Jurmain et al. 364)

            Other than modern humans, chimpanzees are the closest relatives to these australopithecines.  They have similar cranial capacities, use similar tools, and like some of the early hominids, chimps occasionally go on organized hunts for meat.  Other than the fact that A. Ramidus and A. Anamensis were bipedal, they were probably as ape-like as they were human-like. 

            Obviously, the only methods with which australopithecines can be studied are through fossils.  But we do have living chimpanzees which we can study to give us a glimpse at how our earliest ancestors may have behaved.  Like humans and our hominid ancestors, chimps have evolved skillful tool making, and on some occasions walk bipedally.  This is especially true amongst bonobos.  These are the same traits that were being developed by early hominids 5 to 6 million years ago. 

            As chimpanzees are further studied, it is becoming more apparent that their intelligence is much higher than previously thought.  It is believed that chimps have the learning capacity to use spoken language, but their throats and vocal cords are not designed to make consonant sounds.  This eliminates the possibility of chimps actually talking.  However, chimps in captivity have been taught to understand English, communicate through keypads with symbols, and use sign language.  Since early hominids were descendants of the same common ancestor as chimps, they most likely

had the same abilities, if not more, than do modern chimps.  Because of our studies of chimp’s culture and the fossil records of early hominids, we can now ascertain that our ancestors were definitely not idiots, as some scientists like to believe.


Works Cited

 

Brewington, Julie.  “Australopithecus Ramidus--The Earliest Hominid?”  Internet.           available at http://www.mc.maricopa.edu/anthro/origins/ramidus.html.

Jurmain, Robert, et al.  Introduction to Physical Anthropology.  Wadsworth Publishing   Company, Boston, 1997.

Rumbaugh, Duane M.  “Chimpanzee.”  The World Book Encyclopedia.  vol. 3, pp. 471-          473.  Chicago 1988.

 


Research Log

 

Date:  4/25/98     Time:  4:05 p.m.     Weather: sunny and clear, 70 degrees

Focal Chimp:  Jimmy

:05  starring at people through the glass, pushes Blackie backwards to the glass

:10  starring at people through the glass, nodding head repetitively, walks away from    the glass

:15  walks back towards glass, opens his mouth wide, makes faces at people

:20  chewing on an unidentifiable object

:25  presses lips up to the glass, walks to other side of enclosure, makes faces at kids

:30  scratches his head, sticks out his tongue, spits food out onto the glass and licks it off

:35  raises his arms and jumps up and down trying to look tough

:40  lies down with his back facing the glass, watches other chimps in the distance, gets up and walks around, stands up on 2 legs

:45  urinates, moves logs around, swats flies on his head, bounces head up and down, clears brush off of a spot and sits on it

:50  the majority of the people leave and the other chimps come out, Jimmy stays away from the others who are all interacting

:55  gets up and walks on a log, Bondo starts following Jimmy but Jimmy ignores him and walks away, watches the other chimps from the log, I walk up to the glass and Jimmy gets a little agitated

:60  makes faces at little kids who have just entered, walks back and forth across the glass window


Date:  5/2/98     Time: 4:10 p.m.     Weather:  sunny, a few clouds 75 degrees

Focal Chimp:  Jimmy

:05  sniffs around, sits down in the area he sniffed out, runs away

:10  makes faces at people, backs up, pulls up grass, gets angry, jumps up and down, runs up and bashes into the glass as if attacking the men on the other side

:15  briefly gets groomed by another chimp, nods his head, yawns, rolls around on his back

:20  stands up on two legs to act tough, mates with Blackie

:25  presses face up against window, picks stuff out of his eyes and puts it in his mouth, picks his teeth

:30  walks up to a rock, walks on the log, puts his hand in his mouth, eats something, gets off log

:35  watches below as juveniles climb a tree, pokes himself with a stick, gnaws at his wrist, babies try to climb on his back but Jimmy ignores them

:40  gets mad at people and yells, mates with Blackie again

:45  runs across enclosure, makes faces at people, jumps up and down, attacks glass again

:50  rocks back and forth, another chimp approaches him and they chase each other around, Jimmy sits up while another chimp jumps on him, Jimmy ignores the chimp trying to jump on him

:55  comes up to the glass, walks around looking at all the people

:60  sits down in front of glass, urinates, swats flies on his head, walks to grassy area and sits


Date:  5/13/98     Time:  9:25 a.m.     Weather:  clear and sunny, seventy degrees

Focal Chimp:  Jimmy

:05  walks on log, eats an orange, stares at me, mates with Blackie

:10  eats oranges and onions, salvages through grass for food, drinks water off the ground

:15  walks across glass looking at kids who just entered, still eating

:20  walks over to 2 other chimps, still eating, sits on a log, returns back to glass

:25  gets annoyed as large group of people enters, climbs up rock, pushes Blackie off the rock and brings her up to the glass as if he is going to mate, but doesn’t

:30  climbs back up to rock, eating greens, walks to a different rock, urinates, walks to logs

:35  walks over to juveniles, drinks water off a rock, approaches people who just entered, eats sunflower seeds

:40  drinks, eats sunflower seeds and spits out the shells

:45  walks around in front of glass, stares at kids, rolls over on his back, stands up and rolls over again, still eating sunflower seeds and spitting out the shells

:50  still eating sunflower seeds and spitting out the shells right in front of the glass, other chimps run off, Jimmy imitates people’s faces

:55  walks across enclosure, sits with his back to glass, still eating sunflower seeds

:60  goes over to log, walks over to a rock, sits down, gets back up and walks back over to logs