Border Cave Research Articles

The origin of modern anatomy: By speciation or intraspecific evolution?

Abstract“Speciation remains the special case, the less frequent and more elusive phenomenon, often arising by default” (p 164).1Over the last thirty years, great progress has been made regarding our understanding ofHomo sapiensevolution in Africa and, in particular, the origin of anatomically modern humans. However, in the mid‐1970s, the whole process ofHomo sapiensevolution in Africa was unclear and confusing. At that time it was widely assumed that very archaic‐looking hominins, also called the “Rhodesioids,” which included the specimens from Kabwe (Zambia), Saldanha (South Africa), and Eyasi (Tanzania), were spread over wide parts of the continent as recently as 30,000 or 40,000 years ago. Yet, at the same time, there were also indications from the Omo Kibish skeletal remains (Ethiopia) and the Border Cave specimens (South Africa) that anatomically modern humans had already been present somewhat earlier than 100,000 years B.P.2,3Thus, it was puzzling how such early moderns could fit in with the presence of very archaic humans still existing in Eastern and Southern Africa only 30,000 years ago.

Bayesian analysis of ESR dates, with application to Border Cave

Methods for Bayesian statistical analysis of stratigraphically related radiocarbon dates have been in use for over a decade. This paper extends these techniques to stratigraphically related ESR dates, allowing estimation of the dates of events not directly dated. A hierarchical model of the uncertainties in ESR dating is developed, to account for the correlation of error terms between samples. Using the new method, an analysis is made of the dating at Border Cave, Kwa Zulu Natal, South Africa. The results for individual dates and the dating of layer boundaries are more precise than previously obtained. The hominid fossils BC1 and BC2 are placed at either 71–91 ka (95% highest posterior density—hpd) or 152–171 ka (95% hpd) depending on the stratigraphic provenance assigned. BC3 is dated to 66–90 ka and BC5 to 61–72 ka (both 95% hpd). The estimated duration of the Howieson's Poort industry at Border Cave is demonstrated to have significant uncertainty, and the ESR dates, even with the increased precision of this analysis, are unable to decide between hypotheses that the industry lasted 10 ka and that it lasted 20 ka.

Direct dating of human fossils

The methods that can be used for the direct dating of human remains comprise of radiocarbon, U-series, electron spin resonance (ESR), and amino acid racemization (AAR). This review gives an introduction to these methods in the context of dating human bones and teeth. Recent advances in ultrafiltration techniques have expanded the dating range of radiocarbon. It now seems feasible to reliably date bones up to 55,000 years. New developments in laser ablation mass spectrometry permit the in situ analysis of U-series isotopes, thus providing a rapid and virtually non-destructive dating method back to about 300,000 years. This is of particular importance when used in conjunction with non-destructive ESR analysis. New approaches in AAR analysis may lead to a renaissance of this method. The potential and present limitations of these direct dating techniques are discussed for sites relevant to the reconstruction of modern human evolution, including Florisbad, Border Cave, Tabun, Skhul, Qafzeh, Vindija, Banyoles, and Lake Mungo.

On the age of Border Cave 5 human mandible.

An enamel fragment from the Border Cave 5 specimen was analysed with non-destructive ESR combined with laser ablation ICP-MS for uranium profiling. We obtained an age of 74+/-5 ka which fits exactly into the chronological framework that has been previously established for Border Cave by a variety of dating techniques. The result lays at rest the view that BC5 could be of Iron Age, as was implied by (Journal of Human Evolution, 31 (1996) 499) based on nitrogen contents and infra-red splitting factors.

Three case studies used to reassess the reliability of fossil bone and enamel isotope signals for paleodietary studies

The emphasis on tooth enamel for extraction of stable light isotope signals from the mineral phase of archaeological and paleontological calcified tissues is based on the widespread understanding that enamel remains a relatively closed system, while bone does not. Twenty years ago, however, Sullivan and Krueger’s groundbreaking study demonstrating the potential of stable carbon isotopes from the mineral phase relied entirely on bone apatite samples from archaeological sites. Further effort to test whether diagenetic effects in bone mineral may be circumvented remains important because bone apatite yields dietary information about adult life-stages beyond the discrete snapshots obtainable from enamel. In this paper we re-examine the grounds for exclusion of bone apatite as sample material, using case studies drawn from three sites which differ in age and depositional conditions. We use 13C/ 12C, 18O/ 16O, 87Sr/ 86Sr, and Fourier transform infrared (FTIR) spectroscopy data from three sites (Reunion Rocks, Border Cave, and Makapansgat Limeworks) to show that, while enamel is not a closed system, it nevertheless retains biogenic isotopic signals. In addition, bone signals may be surprisingly well preserved where fossilisation pathways have induced ‘enamel-like’ crystallisation changes.

Radiocarbon dating from 40 to 60 ka BP at Border Cave, South Africa

We present 21 radiocarbon dates on 19 charcoal samples from the sedimentary sequence preserved in Border Cave, South Africa. The background radiocarbon activity for charcoal from the cave was determined to be 0.050±0.018 percent modern carbon, from the analysis of a radiocarbon-dead sample from unit 5WA. Radiocarbon ages for individual samples ranged from 25.2 to >58.2 ka BP. The error-weighted mean ages for successively older strata are 38.5+0.85/−0.95 ka BP for unit 1WA, 50.2+1.1/−1.0 ka BP for units 2BS.LR.A and 2BS.LR.B, 56.5+2.7/−2.0 ka BP for unit 2BS.LR.C and 59.2+3.4/−2.4 ka BP for unit 2WA. This radiocarbon chronology is consistent with independent chronologies derived from electron spin resonance and amino acid racemization dating. The results therefore provide further evidence that radiocarbon dating of charcoal by the ABOX-SC technique can yield reliable radiocarbon ages beyond 40 ka BP. They also imply that Border Cave 5, a modern human mandible, predates >58.2 ka BP and that the Middle Stone Age (Mode 3)—Later Stone Age (Mode 5) transition of Border Cave was largely effected between ∼56.5 and ∼41.6 ka ago.

Border Cave revisited: a revised ESR chronology

In view of a decade of progress in ESR dating we have revised the ESR chronology of Border Cave. A detailed gamma ray survey in 1994 and newly calculated beta attenuation data led to total dose rate estimations that are between 0 and 30% smaller than previously estimated. Accordingly, the resulting ESR age estimates are between 0 and 30% older. The ESR dates are now in good agreement with independent age estimates, particularly14C and amino acid racemization. New ESR dates for the lowermost dated sedimentary layer, 5 WA (white ash), indicate that the sedimentation of the sequence started around 200ka ago.

Earliest modern humans in southern Africa dated by isoleucine epimerization in ostrich eggshell

The oldest anatomically modern human remains are beyond the range of radiocarbon dating, and associated deposits lack material suitable for most other dating methods. Consequently, age estimates for early human skeletal material and correlative stratigraphic horizons in southern Africa are frequently based on paleoclimatic correlations to the deep-sea record and extrapolated sedimentation rates, both of which incorporate a number of untested assumptions. Here we focus on one substage of the Middle Stone Age of southern Africa, the Howiesons Poort industry, a distinctive culture-stratigraphic marker in sequences south of the Zambezi. Anatomically modern human skeletal material has been found associated with, or even older than the Howiesons Poort layer in stratified deposits at Border Cave and Klasies River main site. We have dated or bracketed the Howiesons Poort horizon at Border Cave, Boomplaas Cave and Apollo 11 Cave, three stratified cave sites in southern Africa, based on the extent of isoleucine epimerization in associated ostrich eggshells. We conclude that the Howiesons Poort lithic industry is bracketed by limiting dates of 56 and 80 ka, and is most likely centered on 66±5 ka. Anatomically modern human remains in deeper levels are more than 100 ka old, lending support to the hypothesis of an African origin for Homo sapiens.

Diagenesis of bone from Border Cave: implications for the age of the Border Cave hominids

Hominids from the site of Border Cave purportedly provide direct evidence for the early emergence of anatomically modern humans (AMH) in Southern Africa. ESR dating of Border Cave faunal enamel has confirmed the antiquity of the sediments, although questions persist regarding the provenience of the hominid specimens. Here we establish that, at Border Cave as elsewhere, bone mineral crystallinity, measured as the infrared (IR) splitting factor (SF), distinguishes between contemporary and recent bones on the one hand, from Middle Stone Age (MSA) bones on the other. Two hominid postcranial bones recovered in 1987 from a slumped profile, having essentially no provenience, are shown to have crystallinity indices consistent with the MSA fauna, while two of the purportedly ancient AMH specimens (BC3 and BC5) have values consistent with recent fauna. We conclude that BC3 and BC5 may be considerably younger than the sediments from which they were recovered.

A morphological and histological study of the human humerus from Border Cave

The fragmentary hominid humerus shaft discovered at Border Cave in 1987 can be studied from several perspectives. A small flake of cortical bone yields histological evidence for an age at death late in the fifth decade, plus relatively small osteons (total osteon area). Shaft dimensions, cross-sectional characteristics at midshaft and estimated length are compared with values from Late PleistoceneHomo sapiensand to humeri from the Later Stone Age in South Africa (C14 dated 2090–9750 BP). The Border Cave humerus is platybrachic, has a %CA (cortical area/total area×100) of 82·7 at midshaft, and is estimated to have been about 330 mm in length, or less. It is morphologically most similar to Neanderthal humeri, suggesting that it is “archaic”. Its robustness and its small osteons are consistent with Middle Stone Age antiquity. Some features suggest that it may represent a larger, more robust version of the Later Stone Age population. This in turn suggests possible continuity from archaic to modern infracranial anatomy in southern Africa.

A morphological and histological study of the human humerus from Border Cave

The fragmentary hominid humerus shaft discovered at Border Cave in 1987 can be studied from several perspectives. A small flake of cortical bone yields histological evidence for an age at death late in the fifth decade, plus relatively small osteons (total osteon area). Shaft dimensions, cross-sectional characteristics at midshaft and estimated length are compared with values from Late Pleistocene Homo sapiens and to humeri from the Later Stone Age in South Africa (C14 dated 2090–9750 BP). The Border Cave humerus is platybrachic, has a %CA (cortical area/total area×100) of 82·7 at midshaft, and is estimated to have been about 330 mm in length, or less. It is morphologically most similar to Neanderthal humeri, suggesting that it is “archaic”. Its robustness and its small osteons are consistent with Middle Stone Age antiquity. Some features suggest that it may represent a larger, more robust version of the Later Stone Age population. This in turn suggests possible continuity from archaic to modern infracranial anatomy in southern Africa.

Modern Human Origins : Evidence from the Near East

Near East is large and anatomically diverse. On the basis of cranial and skeletal features, this sample has been divided into two distinct groups. One grouping, composed of specimens from the sites of Shanidar, Tabun, Wadi Amud and perhaps Kebara, possesses features similar to those of the European Neandertals. The other group, represented by the samples from the Qafzeh and Skhul caves, possesses many features linking them with modern humans. Neither of the two major models proposed to account for modern human origins, rapid replacement, or regional evolutionary continuity, emphasize these sizable collections from the Near East in their formulations. This is understandable because the fossil and archaeological data from the Near East do not provide supporting evidence for either model. Close examination of the rapid replacement model indicates that this widely held notion that the origins of anatomically modern humans took place on the African continent is not currently supported by the evidence. Two kinds of evidence have been used to support the rapid replacement model : comparative molecular and fossil data. The molecular evidence is from comparisons of the nuclear and mitochondricd genetic material from a number of living human populations. These data document a relatively recent common origin for modern human populations, but they are not able to specify the continent where this origin occurred. The data can be equally interpreted to place this origin locale in Africa or in Eurasia. Thus, the molecular data does not support an "Out of Africa" model as being any more likely than one that suggests an origin in Asia. The fossil evidence in support of the rapid replacement model comes from three sub-Saharan sites : the Kibish Formation along the Оmо River in southern Ethiopia; Border Cave, from the border area between South Africa and Swaziland; and from Klasies River Mouth Cave on the southern coast of South Africa. Each of these fossil samples have difficulties which make their acceptance as representatives of early modern humans disputable. The Klasies River Mouth sample is fragmentary and incomplete, making any anatomical judgements about its modernity provisional. There continue to be questions about the contemporaneous association of the Border Cave hominids with the ancient archaeological levels in which they were found. Finally, the dating techniques used to place the Оmо Kibish fossils at more than 100,000 years ago are suspect when utilized on materials like shells. Thus, the currently earliest known, well documented anatomically modern human samples are those from the Skhul and Qafzeh caves. This evidence, however, is not complete enough to allow us to draw any conclusions about the time and place of modern human origins. Indeed, through much of the latter part of the Middle Pleistocene and almost all of the Late Pleistocene, there is virtually no archaeological or fossil hominid evidence from much of southern Asia. Reasonably, at the present time, given the quality of evidence documenting an African origin for modern humans, as well as the lack of data from southern Asia, an Asian origin must be considered as equally plausible.

The Pleistocene Later Stone Age south of the Limpopo River

The earliest Later Stone Age (LSA) industries from southern Africa are microlithic and unstandardized and include the bipolar technique. The dating of these industries is controversial and the earliest microlithic industry is said to occur at Border Cave at about 39,000 B.P. By 18,000 B.P. a bladelet tradition was established and this was replaced in many parts of southern Africa, at about 12,000 B.P., by a widespread and prolific nonmicrolithic industry, characterized by side-struck flakes. The late Pleistocene environment was colder than present, with particularly harsh conditions during the Last Glacial Maximum (LGM), between about 20,000 and 18,000 B.P. Populations may have been isolated because archaeological visibility is low during the LGM and decreases further after the LGM. After 13,000 B.P. there is a dramatic increase in sites and this implies that there may have been widespread colonization of territory previously unoccupied for tens of thousands of years. By the end of the late Pleistocene there was a change in hunting patterns, in parts of southern Africa, from an emphasis on the capture of large, gregarious grazers to an emphasis on small, solitary browsers. Social complexity increased during the late Pleistocene, and by 12,000 B.P. it seems possible that Stone Age people were observing some social practices recorded historically among Bushmen (San).

Last interglacial and holocene altithermal environments in South Africa and Namibia: micromammalian evidence

Climatic interpretations are derived indirectly from evidence for vegetation changes based on the remains of micromammals (small rodents and shrews) from archaeological sites. Thus far, only Border Cave has provided evidence apparently referable to the earlier altithermal in oxygen-isotope substage 5e. Vegetation zones, and by implication climatic zones, apparently extended 3° and more south of their present southern limits. Rainfall may have been up to 100% more than it is today and much more seasonal, with drier winters. Mean annual temperatures were perhaps about 1°C higher on other evidence. Eight other sites provide evidence concerning conditions during the Holocene altithermal (7000-6000 yr B.P.). The evidence seems to indicate relatively low annual precipitation in the main, summer-rainfall, region and an extended rainfall season in the southwestern, winter-rainfall, region. It is less clear whether or not annual rainfall was relatively high at this time in the latter region although in the Namib desert conditions were apparently wetter. This tends to agree with the dry-period analogue of Cockcroft et al. (1987) and would imply reduced seasonality of precipitation throughout the region in contrast to the situation during the earlier altithermal. Apparent conflict with palynological evidence may be explainable but requires further examination.

Pleistocene geochronology and palaeothermometry from protein diagenesis in ostrich eggshells: implications for the evolution of modern humans.

Proteinaceous residues incorporated within the crystal structure of ostrich eggshells (OES) are retained without loss over geological time exceeding 10 million years. Degradation of the polypeptides, including hydrolysis to smaller peptide fragments and eventual release of free amino acids, decomposition, and racemization and epimerization occur at regular, predictable rates dependent on ambient temperature. The extent of isoleucine epimerization (aIle/Ile ratio) in OES follows linear first-order reversible kinetics in controlled-temperature laboratory simulations of time up to an aIle/Ile ratio in excess of 1.0. The hydrolysis of leucine also follows a predictable pattern, but deviates from first-order kinetics. A nonlinear mathematical model has been developed that adequately describes the pattern of leucine hydrolysis through a wide temperature range. Arrhenius parameters were derived from laboratory experiments combined with rate constant values found for 14C-dated OES from stratified caves in southern Africa. These parameters for isoleucine epimerization and leucine hydrolysis differ by ca. 10%, allowing the simultaneous solution of the two equations for temperature, independent of sample age. Although the uncertainty of the simultaneous temperature is relatively high (+/- 10 degrees C), it provides an effective means of identifying burned samples. If sample age is known, palaeotemperatures (the integrated thermal history experienced by an eggshell as opposed to an 'instantaneous' temperature) can be calculated with a precision of better than +/- 1 degrees C. The ages of levels at Border Cave, South Africa, from which anatomically modern human skeletal remains have been recovered, are dated by the extent of isoleucine epimerization in associated OES.(ABSTRACT TRUNCATED AT 250 WORDS)

Southern Africa and modern human origins.

This paper argues that southern Africa was a remote part of the Old World in the late Pleistocene (125-10 ka ago). Because of this isolated position there was continuity without significant replacement in the resident population. Isolation and the relatively recent spread of agriculture to the region has allowed a section of this population to survive into the present. They are the Bushmen (San). Studies of geographic patterning in conventional genetic markers and mitochondrial DNA indicate that the Bushman clade has a long evolutionary history in southern Africa. Estimates of more than 100 ka for the continued presence of this population in the region are supported in archaeological investigations of sites with long sequences such as Klasies River main site and Border Cave. Human remains dating to the earlier part of the late Pleistocene have been recovered from these sites and the samples form a morphological series with the Klasies River remains possibly 20 ka older than those from Border Cave. There is no fossil record for the later Pleistocene, however, at a period when selection for a gracile morphology may have been pronounced. The cultural associations in the earlier late Pleistocene are with the Middle Stone Age. Expressions of cultural 'style' and the occurrence of similar artefact design types in the Middle and Later Stone Ages can be interpreted with reference to the ethnographic present. Temporal continuity can be shown in the geographical distribution of stylistic markers and this suggests participation in a shared cognitive system.(ABSTRACT TRUNCATED AT 250 WORDS)

Metrical reconsideration of the Skhul IV and IX and Border Cave 1 crania in the context of modern human origins.

The "out-of-Africa" models for origins of modern Homo sapiens incorporate Skhul as one site documenting that early origination. However, only Skhul V is usually considered in the comparative craniology of the question, neglecting the other substantial crania, Skhul IV and IX. Craniometric comparison demonstrates that IV and IX amplify the picture of continuous gradations of Neandertal-to-modern variations throughout the Levant; much variation is thus represented within this one site, raising serious questions about Neandertals and moderns being discrete and long-separated species. Qafzeh 6 too is craniophenetically closer to Neandertals than to the true anatomically modern people of the European Upper Paleolithic. Proper distance analysis of Border Cave 1 cranium shows it is actually far removed from modern African populations. References to Qafzeh, Skhul, and Border Cave as "fully anatomically modern" require reconsideration.

The environment of early modern humans at Border Cave, South Africa: micromammalian evidence

An enlarged sample of micromammalian remains from Border Cave has permitted re-evaluation of vegetational and climatic conditions at the site from its earlier occupation, apparently about 130 kyr B.P. The indication is that vegetation in the region was initially woodland analogous to miombo ( Brachystegia) woodland which today occurs a minimum of 3° latitude north of the site. Rainfall would have been 25–100% higher than it is today and more seasonal, with drier winters. Mean annual temperature may have been similar to or slightly higher than it is today. Thereafter, perhaps in δ 18O stage 5b onwards from around 96 kyr B.P., vegetation and, consequently, rainfall appear to have become much as they are today, namely bush savanna with forest patches supported by rainfall around 800 mm. Temperatures, on the other hand, may have been rather lower than they are today, and it is possible that δ 18O stage 4 is represented during this period. Subsequently, during δ 18O stage 3, the vegetation appears to have been open Acacia nigrescens-Sclerocarya savanna, perhaps preceded by mopane ( Colophospermum mopane), such vegetation types today being found at lower altitudes in neighbouring Swaziland and into the northeastern Transvaal. Rainfall may have been 25–55% lower than it is today and relatively unpredictable while temperatures were marginally lower. These conditions persisted until about 24 kyr B.P. when the cave was apparently abandoned.

ESR dating evidence for early modern humans at Border Cave in South Africa

The archaeological and hominid site of Border Cave (KwaZulu, South Africa) has a stratigraphic sequence covering the Middle and Later Stone Ages (MSA and LSA). It has been proposed that four hominid specimens recovered there (BC1 and BC2 of uncertain provenance, and BC3 and BC5 recovered from MSA layers) represent very early examples of anatomically modern humans, supporting an early late-Pleistocene appearance of modern Homo sapiens in Africa. This early appearance, however, has been questioned, largely because of doubts about the stratigraphic positions associated with the specimens and because of the lack of a reliable chronology for the stratigraphic sequence. We now report on the first comprehensive radiometric dating analysis of Border Cave, using electron spin resonance (ESR) on teeth within sediment layers. BC3 is likely to be approximately 70-80 kyr old, and BC5, 50-65 kyr old. BC1 and BC2 are almost certainly less than 90 kyr old. These results, although younger than some age estimates, support the early occurrence of anatomically modern humans at Border Cave. In addition, our results suggest that the Howiesons Poort lithic industry (approximately 45-75 kyr) and the MSA-LSA transition (approximately 35 kyr) are younger than often believed.

The micromammalian fauna from Border Cave, Kwazulu, South Africa

Abstract The micromammalian fauna from Border Cave is analysed in terms of community composition and structure. Changes in these aspects are interpreted as indicative of changes in vegetation and climate in the vicinity of the cave during the period of deposition. It would appear that vegetation comprised relatively extensive forest or thick bush and dense grass during wetter phases and fairly open savanna woodland, even open grassland, during drier periods. Variation through time in mean mandibular size in two species of Crocidura (musk shrew) was different both in the two species and from what was expected. It now seems likely that the size change constitutes a response to complex phenomena and not simply to changes in temperature. Comparison with the Boomplaas A sequence indicates that the same general pattern of change is reflected at both sites but that there was a greater amplitude of change at Boomplaas A and that 18O stage 4 was dry at this site but wet at Border Cave. Evidence for periodic changes in the distribution of various species, and in some cases the mutually exclusive occurrence of ecologically equivalent species, has implications for the zoogeography of the species involved. In particular, the occurrence of Pelomys fallax (creek rat) in the lower half of the sequence is of interest in view of its present distribution 600 + km north of Border Cave.