Pathology of Chimpanzee Skeletons At Kibale

Paleopathology, for all practical purposes, is the study of the diseases and traumas that affect humans in the past. Necessarily, it is restricted to the study of the skeleton which severely limits the scope of what diseases can be studied. Even with that restriction a wide variety of questions can be addressed. We can, for example, ask how the change in lifestyle from hunter-gatherer to agriculturalist impacted human health. Or we can look at disease patterning in a given lifestyle. We can also look at whether disease and trauma differentially affect a given group such as young versus old or male versus female.
Since chimpanzees are our closest living relatives, understanding the diseases and traumas that impact the chimp skeleton might shed some light on human evolution. We can ask, for example, what selective factors impact chimpanzees It goes without saying that it would also be helpful to conservation biologists as well. There is a growing body of literature on the subject.


One such paper concerns skeletal trauma in chimpanzees at Kibale National Park. The paper analyzed the remains of twenty chimpanzees collected at Kibale National Park during 1997-2000. Of these twenty, twelve included post cranial material, while eight were represented by craniums or skulls alone. The sample included six females, eleven males, and three of undetermined sex. Age composition was as follows: four juveniles (age 3-10 years), five young adults (age 10-20 years), six prime adults (age 20-35 years), and six old adults (age 35+ years) – the paper does not explain where the extra individual came from.
Four different categories were looked at: arthropathy, trauma, bone formation and loss, and developmental abnormalities.
Arthropathy
All but five skeletons showed signs of moderate to severe degenerative joint disease (DJD). In thirteen of these the DJD was related to trauma, while in two (both female) the DJD was related to old age. In humans, one of the primary locations for DJD is in the lumbar spine, not so in chimpanzees (however, see below). In the chimpanzees, the primary location is in the extremities (and is more prevalent in the forelimbs than the hindlimbs). Most of the crania showed signs of severe degenerative arthitis at the temporo-mandibular joint (see below).
Trauma
Thirteen individuals showed signs of healed trauma, but this figure may have been biased downward due to the fact that postcranial material was lacking in eight of the individuals. Eleven of the individuals postcranial material showed signs of healed trauma. Four of these had long bone fractures as well as healed rib or hand fractures. In total, seven individuals had fractures in their hands (which seem to be in the metacarpals and phalanges). Eight crania had fractures and seven (five females and 2 males) and depressed fractures indicative of bites. One female had five depressed fractures attributes to bites. One of the males had a tooth fragment, from an unidentified species, embedded in his ulna.
Bone Formation and Loss
Five specimens displayed periostitis related to trauma. Three specimens displayed evidence of ossified ligaments or tendons. There was also a few crania and mandibles showing signs of infection.
Developmental Abnormalities
One individual showed bilateral accessory naviculars in the feet, while another displayed a rare hip dysplasia called coxa valga.
What Does It Mean?
So how can these patterns of trauma, and so forth, be explained? There are actually several causes at work. The first involves falls from the canopy which accounts for a large majority of the trauma observed. There is some data which indicates that safety during climbing has had an impact on chimpanzee morphology. It can also be seen in the fact that chimpanzees prefer the energetically more expensive terrestrial locomotion to arboreal locomotion.
It has been proposed, based on other studies, that cranial trauma shows sex specific patterns. Some of this was seen in the Kibale sample. Specifically, in females the crania were more likely to show fractures, whereas in males the face was more likely to show fractures. Such was not the case with bitemarks.
When compared to the chimpanzees at Gombe, some interesting differences are seen. In the Gombe chimps there is no evidence of TMJ problems. Fractures in the hands and feet are much more prevalent at Kibale and, this I find really interesting, DJD is found in the lumbar area much more frequently at Gombe. I would have expected a repeat of the Kibale pattern (i.e. more prevalent in the extremities than in the spine) and have to wonder what the chimpanzees at Gombe were doing differently.
There is one form of trauma I did not mention above. That involves trauma due to contact with humans. At Gombe there are a few skeletons which show evidence of poliomyeltitis – contracted via human contact. At Kibale, however, there is evidence of death by gunshot and by machete. There is also evidence for amputation of hands and feet, and mutilation of fingers and toes all due to snares set for game animals.
Chimp pathology.JPGFig. 2. Examples of healed traumatic injury in the Kibale chimpanzees. A: Depressed lesion (probable bite wound), indicated with white circle, on cranial vault of KFB 3. B: Upper limbs long bones of KFB156 showing the smaller left arm, which resulted from a left hand injury. C: The mandible of KVC1, showing the fractured and extensively modified right ramus and condyle. D: Fused metatarsals and distal tarsal row (all cuneiforms and cuboid) of KFB 152. E: Extensively remodeled right pelvis of KFB107, the probable result of a fall from height.
Literature Cited
Carter, Pontzer, Wrangham, and Peterhans (2008) Skeletal Pathology in Pan troglodytes schweinfurthii in Kibale National Park, Uganda. AJPA 135(4):389-403

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5 Responses

  1. A full copy of the paper appears to be here (PDF).
    From your blog article:

    The first involves falls from the canopy which accounts for a large majority of the trauma observed. There is some data which indicates that safety during climbing has had an impact on chimpanzee morphology. It can also be seen in the fact that chimpanzees prefer the energetically more expensive terrestrial locomotion to arboreal locomotion.

    I have several observations, starting with the fact that more information on the subject can be found in Herman Pontzer and Richard W. Wrangham: “Climbing and the daily energy cost of locomotion in wild
    chimpanzees: implications for hominoid locomotor evolution
    ” Journal of Human Evolution 46 (2004) 315–333. A full copy of the PDF is available online at http://artsci.wustl.edu/~hpontzer/Papers/Pontzer&Wrangham2004JHE_ChimpClimbing.pdf.
    AFAIK the relative costs of vertical and horizontal motions become greater with increasing body mass, pointing to a recent increase in size of chimpanzees and bonobos, possibly in parallel after the two species diverged.
    Assuming (as I do) that the last common ancestor of the great apes was fully bipedal (similar in formation to Australopithecus), the initial modifications for brachiation likely occurred before the increase in body size. I would speculate a size somewhere equivalent to that of modern Hylobatidae, although with shorter arms.
    The hip modifications for brachiation (lenghening of the pelvis, reduction in number of lumbar vertebrae) may well have occurred during the size increase. Filler claims (“The Upright Ape“) that the hip changes in chimp/bonobo and gorilla are convergent evolution rather than descended from a common ancestor. If so, these lineages may have independently developed specializations for brachiation (relative to an Australopithecus-like ancestor).

  2. Or, it could be that large body size and climbing safety is what forced the large hominoids and hominids onto the ground and into a more terrestrial style of locomotion…

  3. Or, it could be that large body size and climbing safety is what forced the large hominoids and hominids onto the ground and into a more terrestrial style of locomotion…

    I was actually assuming that. Have you seen Origin of Human Bipedalism As an Adaptation for Locomotion on Flexible Branches by S. K. S. Thorpe, R. L. Holder, and R. H. Crompton, (mentioned by Ed Yong)? (May require a free registration.) I was thinking of this as well as Filler’s theories.
    My point is that until body size increased, something like a miniature (or perhaps very slim) Australopithecus could have been quite comfortable both in the upper terrace and on the ground. As body size increased, the hip changes would have made bipedalism much harder, because the body would have lost its ability to swing the shoulders opposite from the hips (see Filler). Thus, knuckle-walking. Further size increases would then have led to a general abandonment of brachiation and obligate terrestriality.
    AFAIK, the last word is definitely not in on knuckle-walking. I’m still tracking down the various letters etc. on the subject, after discovering how much I can see in Science Mag with a free registration. Still, most of the arguments seem to cover adaptations to shoulder, elbow, and wrist that could be explained by using branches at waist height for support (while scrambling through rough downwood), and boxing (IIRC Wrangham and Petersen discussed the use of fists by most male apes in “Demonic Males“).

  4. Sorry for the delayed response – I’ve been fighting some kind of stomach bug – yes I’ve read Thorpe et al’s paper. Part of the problem, IMHO, is that it is very easy to treat primate locomotion as mutually exclusive behaviors. Primates are very generalized critters and their locomotor behavior reflects this. Which reminds me, after I read the Thorpe et al paper I started a series on primate locomotion that I have never completed, I’ll have to work on that…

  5. Thanks for the response, afarensis.

    Primates are very generalized critters and their locomotor behavior reflects this.

    Yes relative to most mammals (not to mention other lineages). But with at least two important caveats:
    1. Size matters. Due to the square/cube law, the larger an animal is, the more difficult it is for it to perform very well at many different things. Skeletal specializations are both more necessary, and take more weight, vertical movement takes more energy relative to horizontal, etc. Thus any time a lineage increases its size, it comes under strong pressure to specialize, and if it remains a generalist it comes under higher (potential) competitive pressure from dedicated specialists, especially its own cousins. I would see exactly this in the hip modifications for brachiation (which aren’t present in Hylobatids, but are in the larger bonobos and chimps, and especially oran utangs and gorillas). I would also see it in the specializations for knuckle walking, which might not have been necessary for a gibbon-sized animal.
    2. Even without size changes, generalization has limits. For instance, the foot of Australopithecus was probably well adapted to bipedal locomotion on the ground, but also for climbing and bipedal locomotion in the terrace, similar to that described in Thorpe et al. The change to the form in H. ergaster/erectus (and sapiens added a small improvement (I suppose) in ground motion at the cost of a major loss in the terrace. When you say primates are generalized, this sort of exception is fairly common.
    Finally, when you address Thorpe et al, don’t forget the technical comment by Begun, Richmond, and Strait, and response. I would be especially interested in an extended discussion of the merits of knuckle-walking arguments, as they appear to me to be the only major objection to Filler’s theories.

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