Henry M. McHenry

Systematic Butchery by Plio/Pleistocene Hominids at Olduvai Gorge, Tanzania

Human origins research by archaeologists has expanded the evidence of the diet and subsistence activities of ancient hominids. We examine an important component of that evidence, the 1.75-million-year-old faunal assemblage from the FLK Zinjanthropus site at Olduvai Gorge, Tanzania. Skeletal-part frequencies are used to evaluate hominid access to and differential transport of carcass portions of differing nutritional value. Cut-mark frequencies and locations are used to evaluate butchery patterns including skinning, disarticulation, and defleshing of carcasses. In contrast to other recently published assessments of the FLK Zinjanthropus data, we conclude that (1) ancient hominids had full access to meaty carcasses of many small and large animals prior to any substantial loss of meat or marrow bones through other predator or scavenger feeding; (2) ancient hominids were butchering animal carcasses by an efficient and systematic technique that involved skinning, disarticulation, and defleshing; and (3) the FLK Zinjanthropus site represents a place where the secondary butchering of selected carcass portions and the consumption of substantial quantities of meat and marrow occurred.

Evolutionary Relationships among Early Hominids

Although cladistic analysis provides one of the most useful approaches to discovering the phyletic relatiosships among the species of Australopithecus and early Homo, methodological problems continue to beset any attempt to apply it in this context. Two of the most pressing problems are redundancy of traits due to similarity of underlying function and overrepresentation of some anatomical or functional systems in trait lists. In an attempt to mitigate these problems, we collapse our list of 77 traits into sets of traits using two methods. The first method segregates traits into seven groups by anatomical region. The second method segregates traits by function into five complexes which correspond fairly well with recognized trends in the evolution of early hominids (adaptation for heavy chewing, reduction of the anterior dentition, basicranial flexion, increased orthognathism and encephalization). The most parsimonious cladogram describing the relationships among the early hominid species obtained using the original 77 traits or the summary scores from the functional complexes, places Australopithecus afarensis as a sister group to all other hominids. Australopithecus aethiopicus occupies the next branch, leaving A. africanus, A. robustus, A. boisei and Homo as a monophyletic group. The cladogram next separates A. africanus from the remaining hominids and finally divides Homo from A. robustus and A. boisei. Summary scores for anatomical regions produced three equally parsimonious cladograms, one of which was identical to that described above. This result implies that there was a large amount of parallelism in hominid evolution, and that adaptations for heavy chewing evolved separately in the lineage leading to A. aethiopicus and in the lineage leading to A. robustus and A. boisei. Another implication is that Homo descended from an A. africanus-like ancestor and diverged from A. robustus and A. boisei relatively late in hominid evolution by reducing the extent of its adaptation to heavy chewing. Most current phylogenies are not compatible with the cladogram obtained in this study, but are instead compatible with a cladogram obtained when traits related to heavy chewing are used exclusively. The “heavy chewing” cladogram reverses the positions of A. aethiopicus and Homo. Perhaps the reason why most current cladograms resemble the “heavy chewing” cladogram is the over-representation of traits related to heavy chewing in most trait lists.

Phylogenetic Analysis of Early Hominids

The proposal of the new australopithecine species Australopithecus afarensis has led to a multiplicity of hypotheses concerning the evolutionary relationships between the known Pliocene and Pleistocene hominid species. We use phylogenetic analysis to gain a new perspective on the subject. Using 69 traits, we construct a series of 12 complexes, each with a defining polarized morphocline. Four mutually exclusive cladograms are derived from these complexes, the most parsimonious of which implies that Homo habilis and A. robustus/boisei are more closely related to each other than either is to A. africanus and that these three species form a distinct evolutionary group relative to the more primitive A. afarensis. We advocate a phylogeny wherein A. afarensis is ancestral to A. africanus, which is in turn ancestral to A. robustus/boisei and H. habilis. We believe that the evolutionary transition from Australopithecus to Homo involved reduction in the size of the chewing teeth and associated traits leading to a unique derived condition in H. habilis that superficially resembles the primitive condition of A. afarensis. Five other current phylogenies are treated as critiques of this one.

Fossils and the mosaic nature of human evolution.

These new fossils, dates, analyses, and interpretations lead to confirmation and refinement of the mosaic scheme of human evolution as proposed by early evolutionists such as Lamarck, Haeckel, and Darwin. Evolutionary changes in the body adapting our ancestors to bipedalism occurred before 3 million years ago, judging by the completeness of the adaptation in the late Pliocene-early Pleistocene hominids. The skeletons of these early hominids were not identical to those of modern humans, but locomotor behavior was probably human. At about 3 million years ago their brains were relatively small, although internal reorganization may have been taking place. By 2 million years ago a wider range of variation in brain size appears in the fossil record, with an average size somewhat larger than that in earlier hominids. Concomitant with this beginning of brain size increase was the reshaping of the pelvic region, perhaps related to an increase in birth canal size to accommodate larger-brained fetuses. Evidence for tool manufacturing, meat eating, shelter building, and probably food sharing also occurs at about this time, which signals the coming of a new adaptive strategy.

Distal Humerus in Hominoid Evolution

Multivariate analysis of 16 measurements of the distal humerus in samples of hominoids, cercopithecoids, Tertiary hominoid fossils, and early hominids shows the following results: (1) there is a substantial and functionally interpretable difference between the distal humerus of cercopithecoids and hominoids (excluding Hylobates); (2) the Tertiary hominoid fossils resemble the cercopithecoids more than the hominoids although they are in some ways intermediate; (3) the hominid fossil from Kanapoi resembles Homo sapiens very closely; (4) the Kromdraai humerus is intermediate in shape between Pan and other hominoids; and (5) the large fossil hominid from East Rudolf (KNM-ER 739) is unique among the hominoids.

Sexual dimorphism inAustralopithecus afarensis

Abstract This study reassesses body weight sexual dimorphism in A. afarensis by applying equations that predict body weight from hindlimb joint size in a comparative sample of modern apes and humans. The resulting estimates show a level of body size dimorphism in this fossil hominid to be below that seen in modern gorillas or orang-utans, greater than modern species of Pan , and well above modern H. sapiens . This degree of dimorphism fits with the behavioral model proposed by Foley & Lee, 1989 in which A. afarensis lived in large kin-related multimale groups with females that are not kin-related. The moderate level of body size sexual dimorphism found in this study removes one objection to the lumping of all Hadar hominids into a single species.

The first bipeds: a comparison of theA. afarensis and A. africanus postcranium and implications for the evolution of bipedalism

Although the postcranium of Australopithecus africanus is uniquely different from all extant hominoids, it is nearly identical to A. afarensis. This similarity is surprising because the two species are distinctly different in their dental and cranial anatomy. It implies that the unique postcranial configuration seen in these early hominids was a relatively stable adaptation that was not gradually changing through time towards a form more like that seen in Homo. The simplest explanation of this stability is that natural selection was maintaining a structural adaptation for locomotor behaviors unlike those seen in any extant hominoids.

Biomechanical interpretation of the early hominid hip

Abstract A new pelvic fragment from Swartkrans provides the opportunity to analyze the hip joint mechanics of the robust form of early hominid. The function of the lateral support system provided by the abductor muscles of the hip appears to be similar to that of the gracile early hominid from Sterkfontein. The system is well adapted for providing the lateral support necessary for efficient bipedalism. The hip extensor mechanism and hip internal rotatory system also appear to be well adapted for efficient bipedalism in a way very similar to the other early hominids. The conclusion reached is that the robust and gracile forms of South African early hominids were basically similar in their locomotor adaptation and were most likely habitual bipeds.

Bonobos: Generalized Hominid Prototypes or Specialized Insular Dwarfs? [and Comments and Replies]

Neontological, biochemical, and paleontological data indicate that the bonobo, Pan paniscus, is a specialized form that possesses relatively small teeth, is quadrupedally adapted, and is only minimally sexually dimorphic. The various specializations of bonobos could be adaptations to ecological restrictions encountered in the terrestrial island of tropical forest that comprises their home range. Bonobos possess specializations quite different from those present in either Miocene apes or the earliest known hominids and should not be considered as suitable living models of the primitive hominoid or hominid condition.

The postcranium of Miocene hominoids: Were dryopithecines merely “dental apes”?

This paper reviews the non-dental morphological configuration of Miocene hominoids with special reference to the hypothesis of linear relationships between certain fossil species and living analogues. Metrical analysis of the wrist shows thatDryopithecus africanus andPliopithecus vindobonensis are unequivocally affiliated with the morphological pattern of quadrupedal monkeys. Similar analyses of the fossil hominoid elbow shows that they are more cercopithecoid-like than hominoid-like. Multivariate analysis of theP. vindobonensis shoulder in the matrix of extant Anthropoidea indicate that this putative hylobatine fossil shows no indication of even the initial development of hominoid features. The total morphological pattern of theD. africanus forelimb as assessed by principal coordinates analysis of allometrically adjusted shape variables has little resemblance toPan. Likewise, the feet and proximal femora of the Miocene fossils are unlike any living hominoid species. Even theD. africanus skull is similar to extant cercopithecoids in several features. Although ancestors cannot be expected to resemble descendants in every way, the striking dissimilarity between Miocene and extant hominoids seems to eliminate the consideration of a direct ancestor-descendant relationship between specific Miocene and modern forms.