Hominid Lineage Research Articles

On the presumed coevolution of brain size

The maximum potential life span of hominids shows a progressive increase during the evolution from Australopithecus to Homo sapiens. In the corresponding period, from about 2·3 to 0·04 million years ago, an expansion of the hominid brain occurred as well, particularly of those parts which are associated with higher-order brain functions. The rate of evolutionary change of the endocranial volume and longevity per unit time along the hominid lineage suggests a parallel trajectory of both parameters The increase in maximum potential life span, furthermore, was found to be mainly due to the increase in degree of encephalization, which is a measure for the evolutionary progression of the “extra” brain capacity involved in functions beyond normal body requirement. The findings support the hypothesis that brain size and longevity in hominids coevolved.

Hominid and gelada baboon evolution: Agreement between molecular and fossil time scales

The time of origin of the hominid lineage has long been debated. Macromolecular studies have consistently shown genetic distances between living humans and African apes to be quite small. The molecular clock hypothesis proposes that the time of separation of these lineages is relatively recent (in the range of 4–8 million years ago) and not 15 million years or more ago as usually suggested. Three independent molecular comparisons yield a mean estimate of 4.6 million years for the hominid-African pongid divergence. The relationship of Theropithecusand Papiois a parallel case within Primates of two taxa which are quite similar at the molecular level, but which are usually thought to have separated relatively long ago. The two cases of seeming discordance between different lines of evidence are analogous. Each involves a speciation event which eventually resulted in one substantially derived lineage and one or more relatively unchanged lineages. In each case, claims of the antiquity of the divergence event extend to at least twice the age of the first certain appearance of the more derived lineage in the fossil record. Finally, in each case, the molecular clock model suggests a range of possible divergence times that overlaps with the first appearances of undoubted hominids and Theropithecusin the fossil record. This test involving paleontological evidence supports the molecular clock hypothesis.

Zum Ursprung der Hominidae

A fundamental problem of hominisation is the branching of the human lineage leading to the genusHomo from other hominoids. At present discussed hypotheses of a Miocene separation of the pongid and hominid lineage are described under consideration of numerous new fossils from Europe, Asia and Africa. Of special interest is the possibility of an adhominisation of the genusAustralopithecus (includingA. afarensis).

A revision of the Oligocene apes of the Fayum Province, Egypt

AbstractThree years of field excavations in the Oligocene strata of the Fayum Province, Egypt, have yielded more than two dozen new jaws and teeth of fossil apes. This material contributes significantly to our understanding of catarrhine systematics and phylogeny. Here we present a systematic revision of the earliest apes and discuss their relationship with Miocene forms.Two ape species have been recovered from Quarries I and M in the Upper Fossil Wood zone of the Jebel el Qatrani Formation, Aegyptopithecus zeuxis and Propliopithecus (=Aeolopithecus) chirobates. Female Propliopithecus chirobates have small canines which somewhat resemble those of the enigmatic Propliopithecus haeckeli, but have a longer, narrower P3 than the latter. No specimens of either P. haeckeli or Moeripithecus markgrafi have been found in the Upper Fossil Wood zone after ten field seasons, suggesting that these species may occur only lower in the section.Aegyptopithecus and Propliopithecus have no shared derived features that exclude them from the ancestry either of Old World monkeys or apes. Thus, Aegyptopithecus, the better known form, is suitably primitive to have been the ancestor of all later Old World monkeys and apes (and hominids). The possibility of a separate gibbon or hominid lineage going back to the Oligocene is unlikely on present evidence.

Tempo and mode in hominid evolution.

The nature of human evolution has been viewed recently as a specific example of a more general model of evolution termed "punctuated equilibrium". The characteristics of this model are long periods of little or not evolutionary change (stasis) interspersed with periods of rapid (punctuated) morphological change. Careful analysis of the hominid fossil record over the past 4.0 million years, however, suggests no well documented examples of either stasis or punctuation. The evidence for the evolution of the hominid lineage is most reasonably interpreted by a model of more gradual change with periods of varying rates of evolution.

Hominid paleoecology and competitive exclusion: Limits to similarity, niche differentiation, and the effects of cultural behavior

Author(s): Winterhalder, B | Abstract: Fossil evidence from the Plio‐Pleistocene of Africa apparently has confirmed a multi‐lineage interpretation of early hominid evolution. Empirical refutation of the single species hypothesis must now be matched to the evolutionary ecology theory, which can underwrite taxonomic assessment and help to explain sympatric hominid coexistence. This paper contributes to that goal by reassessing the ecological rationale provided for the single‐species hypothesis. Limiting similarity concepts indicate that the allowable ecological overlap between sympatric competitors is greater than the degrees of metric overlap often advanced as standards for identifying fossil species. Optimal foraging theory and the compression hypothesis show that the initial ecological reaction of a hominid to a sympatric competitor would likely be micro‐habitat divergence and possibly also temporal differentiation of resource use. The long‐term, evolutionary response is niche divergence, probably involving diet as well. General niche partitioning studies suggest that diet and habitat are the most common dimensions of niche separation, although temporal separation is unusually frequent in carnivores. The equation of niche with culture, basic to the single‐species hypothesis, has no analytic meaning. Finally, four minor points are discussed, suggesting that (a) extinction is not unlikely, even for a long‐lived and competitively competent hominid lineage, (b)parsimony is fickle, (c)interspecific mutualism may jeopardize survival, and (d)generalists are subordinate competitors, but for hominids, seemingly, successful ones. I argue that analog models of hominid paleoecology should be replaced by the use of zoological and anthropological observations to assess the generality and reliability of ecological theory and comcepts that may encompass early hominids. Copyright © 1981 Wiley‐Liss, Inc., A Wiley Company

Late Tertiary hominoids and human origins

There are two principal hypotheses about the time of the emergence of the Hominidae, the family that includes man: first, the hominid lineage emerged before 16 Myr ago1–4; or second, living apes and man are so similar genetically that they must have diverged later5, perhaps as late as 5 Myr ago6,7. The first hypothesis is supported primarily by fossil evidence, whereas the second is championed by advocates of the molecular clock6,7. Hominid fossils are abundant back to 3.7 Myr (Australopithecus afarenesis)8 but are rare before that. Ramapithecus (16–8 Myr) was once classified as a member of Hominidae, but recent discoveries and interpretations show that it should be placed in its own family, Ramapithecidae9,10. Two fossil specimens classified as members of Hominidae predate A. afarensis, however: a lower molar from Lukeino in central Kenya dating to 6.5 Myr (KNM-LN 335)11 and a mandibular fragment from Lothagam Hill in north Kenya dated at 5–5.5 Myr (KNM-LT 329)12. Does their morphology justify classification as the first members of Hominidae? Their geological age is relatively secure. The Lukeino Formation which is up to 130m thick is bracketed by K/A dates of 7–5.4 Myr11. The deposits from which the Lothagam Hill mandible derives are disconformably overlain by an intrusive basalt sill with a K/A date of 3.7 Myr and are associated with mammalian fauna that yields a biostratigraphical age of 5–5.5 Myr12,13. We report here a morphological study which indicates that the Lukeino molar has cusp proportions similar to the modern chimpanzee and the Lothagam Hill mandible is morphologically intermediate between modern pongids and A. afarensis.

The fossil record and primate phylogeny

Fossils provide the only direct evidence of the evolutionary history of primates. A method of phylogeny reconstruction is outlined which is based on an evaluation of phenetic resemblances of fossils interpreted in their stratigraphic context. This stratophenetic approach to phylogeny involves three successive steps: (1) organization of fossils stratigraphically, (2) phenetic linking of similar forms from adjacent stratigraphic intervals, (3) critical testing—Is the density and continuity of the fossil record sufficient to support the proposed linkings?—Does the proposed phylogeny make sense cladistically?—Does it make sense paleogeographically? Evaluation of the known fossil record of primates, following the stratophenetic approach outlined here, has suggested that microsyopoids are primitive primates and that fossil tarsioids and plesiadapoids form a closely linked group. Early anthropoids link most closely with Eocene adapoids, supporting an adapoid origin of Anthropoidea. Large gaps remain in the fossil record of lemuroid and lorisoid primates: they may have been derived from an Adapis-like Eocene genus, or they may possibly have evolved independently of other primates since the late Cretaceous or the Paleocene. This question is closely related to the problem of whether living Tarsius or modern lemurs and lorises are more closely related to the living higher primates. The fossil record and the paleogeography of Central America suggest that platyrrhines evolved from an early anthropoid stock and may have entered South America from Asia via North America at about the end of the Eocene. Dental remains are the only evidence of Plio-Pleistocene hominids known in sufficient quantities from successive stratigraphic intervals to permit stratophenetic analysis. Studying the stratigraphic distribution of measurements of tooth size in the East Rudolf sample of fossil hominids and comparing this with dental variation in a modern human population suggests the probable presence of two hominid lineages in East Africa throughout much of the Plio-Pleistocene. Study of all dental and skeletal remains in an explicitly stratigraphic and temporal context should help to clarify the course and complexity of early hominid evolution.

The Evolution of Tool-Using and Tool-Making Behaviour

The author attempts partially to reconstruct the behavioural context which coevolved with tool-using and tool-making in the hominid lineage. Three early hominid artefact occurrences are reviewed with special attention paid to artefact attributes, artefact assemblages and the geographical locations of artefact sites. The osteodontokeratic culture is discussed. Ethological studies of free-living nonhuman primates are then reviewed noting behavioural patterns that accompany tool-using behaviour. The author proposes that the emergence of reflexion, innovation, object and symbol manipulation, observational and trial and error learning, intentional and unintentional modelling, and intentional linguistic instruction can be partially reconstructed by archaeological analyses and cross-species comparisons

Primate models for australopithecine sexual dimorphism

AbstractSeveral different models of sexual dimorphism in the South African australopithecines are compared with sexual dimorphism in the living primates. Australopithecine dimorphism is placed in an evolutionary context, and contrasting trends in the hominid and pongid lineages are shown. Evidence suggesting that the australopithecines were an extremely polytypic taxon is presented, and a high level of both inter‐ and intra‐population variation is indicated.

A View of the Hominid Lineage. (Book Reviews: Uniqueness and Diversity in Human Evolution. Morphometric Studies of Australopithecines)

A View of the Hominid Lineage. (Book Reviews: Uniqueness and Diversity in Human Evolution. Morphometric Studies of Australopithecines)

Vertesszöllös and the Presapiens theory

AbstractThe Presapiens theory, suggesting completely separate lineages leading to Neandertals and to Homo sapiens, has recently received a number of setbacks. However, the discovery of two hominids at Vertesszöllös could be corroborating evidence. The teeth of the first individual were described as those of Homo erectus, as were most features of the second, represented by an occipital. The two main characteristics used to support the Homo sapiens classification of the second individual are the long lambda‐opisthion chord and the high cranial capacity, based on a regression using the lambda‐opisthion chord. However, the real position of lambda is obscured by the presence of wormian bones, and the regression used to predict capacity was derived from a sample with more Neandertals than Homo erectus specimens. A comparative treatment of the morphological features and recalculation of the regression suggests that separating the occipital from Homo erectus is not justified. Other evidence indicates Homo erectus specimens as big as Vertesszöllös 2. It is unlikely that two hominid lineages occur in the Mid‐Pleistocene.

Further evidence of lower Pleistocene hominids from East Rudolf, North Kenya.

Twenty new hominid specimens were recovered from the East Rudolf area in 1973. New evidence suggests the presence of at least three hominid lineages in the Plio-Pleistocene of East Africa.