Hominid Fossil Record Research Articles

Lethal coalitionary attacks of chimpanzees (Pan troglodytes troglodytes) on gorillas (Gorilla gorilla gorilla) in the wild

Intraspecies violence, including lethal interactions, is a relatively common phenomenon in mammals. Contrarily, interspecies violence has mainly been investigated in the context of predation and received most research attention in carnivores. Here, we provide the first information of two lethal coalitionary attacks of chimpanzees (Pan troglodytes troglodytes) on another hominid species, western lowland gorillas (Gorilla gorilla gorilla), that occur sympatrically in the Loango National Park in Gabon. In both events, the chimpanzees significantly outnumbered the gorillas and victims were infant gorillas. We discuss these observations in light of the two most widely accepted theoretical explanations for interspecific lethal violence, predation and competition, and combinations of the two-intraguild predation and interspecific killing. Given these events meet conditions proposed to trigger coalitional killing of neighbours in chimpanzees, we also discuss them in light of chimpanzees’ intraspecific interactions and territorial nature. Our findings may spur further research into the complexity of interspecies interactions. In addition, they may aid in combining field data from extant models with the Pliocene hominid fossil record to better understand behavioural adaptations and interspecific killing in the hominin lineage.

Disproportionate Cochlear Length in Genus Homo Shows a High Phylogenetic Signal during Apes' Hearing Evolution.

Changes in lifestyles and body weight affected mammal life-history evolution but little is known about how they shaped species’ sensory systems. Since auditory sensitivity impacts communication tasks and environmental acoustic awareness, it may have represented a deciding factor during mammal evolution, including apes. Here, we statistically measure the influence of phylogeny and allometry on the variation of five cochlear morphological features associated with hearing capacities across 22 living and 5 fossil catarrhine species. We find high phylogenetic signals for absolute and relative cochlear length only. Comparisons between fossil cochleae and reconstructed ape ancestral morphotypes show that Australopithecus absolute and relative cochlear lengths are explicable by phylogeny and concordant with the hypothetized ((Pan,Homo),Gorilla) and (Pan,Homo) most recent common ancestors. Conversely, deviations of the Paranthropus oval window area from these most recent common ancestors are not explicable by phylogeny and body weight alone, but suggest instead rapid evolutionary changes (directional selection) of its hearing organ. Premodern (Homo erectus) and modern human cochleae set apart from living non-human catarrhines and australopiths. They show cochlear relative lengths and oval window areas larger than expected for their body mass, two features corresponding to increased low-frequency sensitivity more recent than 2 million years ago. The uniqueness of the “hypertrophied” cochlea in the genus Homo (as opposed to the australopiths) and the significantly high phylogenetic signal of this organ among apes indicate its usefulness to identify homologies and monophyletic groups in the hominid fossil record.

The age-related maturational pattern of the human subarcuate fossa (petromastoid canal). Preliminary results from the application of a new three-dimensional analytical approach

The subarcuate fossa, or petromastoid canal, is a hypostotic feature of the temporal bone used for assessing the age at death of immature individuals. The present study uses the high-resolution micro-CT record of 20 extant human infant and juvenile temporal bones to more precisely assess the age-related maturational pattern of this bony structure. In the perspective of the application of our analytical protocol to the study of the hominid fossil record, the main goals of this contribution are to extend the amount and to improve the quality of the linear and volumetric information on the human subarcuate fossa by the application of new 3D imaging techniques.

HUMAN UNIQUENESS, THE OTHER HOMINIDS, AND “ANTHROPOCENTRISM OF THE GAPS” IN THE RELIGION AND SCIENCE DIALOGUE

Abstract. The concept of human uniqueness has long played a central role within key interpretations of the hominid fossil record and within numerous theological understandings of the imago Dei. More recently, the status of humans as evolutionarily unique has come under strong criticism owing to the discovery of certain nonhuman hominids who, as language and culture‐bearing beings, lived as contemporaries with early anatomically modern humans. Nevertheless, many scholars, including those in the field of religion and science, continue to interpret the remains of these other hominids in light of empirically ungrounded implicit assumptions about human uniqueness, which the author calls “anthropocentrism of the gaps.” This paper argues that “anthropocentrism of the gaps” is philosophically unwarranted and thus should not be assumed by scholars in religion and science when evaluating contemporary findings in paleoanthropology.

Australopithecus sediba Hand Demonstrates Mosaic Evolution of Locomotor and Manipulative Abilities

Hand bones from a single individual with a clear taxonomic affiliation are scarce in the hominin fossil record, which has hampered understanding the evolution of manipulative abilities in hominins. Here we describe and analyze a nearly complete wrist and hand of an adult female [Malapa Hominin 2 (MH2)] Australopithecus sediba from Malapa, South Africa (1.977 million years ago). The hand presents a suite of Australopithecus-like features, such as a strong flexor apparatus associated with arboreal locomotion, and Homo-like features, such as a long thumb and short fingers associated with precision gripping and possibly stone tool production. Comparisons to other fossil hominins suggest that there were at least two distinct hand morphotypes around the Plio-Pleistocene transition. The MH2 fossils suggest that Au. sediba may represent a basal condition associated with early stone tool use and production.

Comparative expression analysis of the phosphocreatine circuit in extant primates: Implications for human brain evolution

While the hominid fossil record clearly shows that brain size has rapidly expanded over the last ∼2.5 M.yr. the forces driving this change remain unclear. One popular hypothesis proposes that metabolic adaptations in response to dietary shifts supported greater encephalization in humans. An increase in meat consumption distinguishes the human diet from that of other great apes. Creatine, an essential metabolite for energy homeostasis in muscle and brain tissue, is abundant in meat and was likely ingested in higher quantities during human origins. Five phosphocreatine circuit proteins help regulate creatine utilization within energy demanding cells. We compared the expression of all five phosphocreatine circuit genes in cerebral cortex, cerebellum, and skeletal muscle tissue for humans, chimpanzees, and rhesus macaques. Strikingly, SLC6A8 and CKB transcript levels are higher in the human brain, which should increase energy availability and turnover compared to non-human primates. Combined with other well-documented differences between humans and non-human primates, this allocation of energy to the cerebral cortex and cerebellum may be important in supporting the increased metabolic demands of the human brain.

Thirty-Five Years of Paleoanthropology

When we published our first joint paper on human evolution back in early 1975 (Eldredge and Tattersall 1975), the world of human evolution was a very different place. For a start, it was populated by a much smaller cast of characters. Not only was paleoanthropology itself a much tinier enterprise than it is today, but the sum total of hominid fossils known was hugely smaller. The riches of the Turkana Basin in northern Kenya had only just begun to be explored. The iconic fossil “Lucy” had yet to be found in Ethiopia, and indeed, the Hadar area from which she came had only just been recognized for the palaeoanthropological treasure trove it has turned out to be. Now near-mythic names such as Atapuerca in Spain and Dmanisi in Georgia were yet to become part of the paleoanthropological vocabulary. And such lesser but nonetheless significant names as Ceprano, Drimolen, and Buia had still to fall even on professional ears. Yet even more foreign to modern eyes than the small fossil pond—today we can no longer complain about an “inadequate” human fossil record, much as we’d like to have more—was the prevailing way of looking at the human evolutionary story. Back in the 1970s, the view of the hominid fossil record was fairly unrelentingly minimalist. Under the sway of the Evolutionary Synthesis as it was imported into paleoanthropology in the early 1950s, students of human evolution generally sought to minimize the diversity they perceived in the known record. A single lineage struggling like a green tendril toward the light was the preferable view, and even though by the late 1960s discoveries in Kenya had rendered the strictest version of this model untenable (the “robust” australopiths had to be recognized as a side branch), there was still a general desire to simplify the picture as much as possible. This was, of course, an example of what might be called “human exceptionalism”: Since there is undeniably only one species of human on the planet today, there is an understandable desire to reconstruct our phylogeny by projecting Homo sapiens back into the past through a chain of increasingly primitive extinct species. And although among primates (and mammals) in general there is an unmistakable signal in the fossil record as well as in the modern fauna of diversity— successful forms tend to become more diverse, not to strive toward a particular goal—hominids were regarded as an exception because they possessed culture, an elusive expression of behavioral complexity that “broadened” their ecological niche to the extent that no more than one species of our kind could exist at any one time. When we began our joint investigations of human evolution in the early 1970s, the “cladistic revolution” was in full swing at least in certain corners of the American Museum of Natural History, where we both worked. And we were both highly sensitive to zoological diversity, one of us as a student of trilobites, a highly varied group of Paleozoic invertebrates, and the other as an aficionado of the lemurs, an insular group of primates inMadagascar that has diversified to an astonishing degree. We were hardly surprised, then, to find that the hominid fossils we looked at did not conform to any of the more or less linear views of human evolution that then prevailed. In particular, the cladogram we came up with (to I. Tattersall Division of Anthropology, The American Museum of Natural History, Central Park West at 79th St., New York, NY 10024, USA

Mandibular Fossa Morphology in the Ngandong and Sambungmacan Fossil Hominids

There has been debate in recent years concerning the significance of the mandibular fossa morphology in the Ngandong and Sambungmacan hominids. These fossils lack a postglenoid process and their squamotympanic fissure runs along the apex of the fossa for its entire length. This configuration differs from that seen in other fossil and modern humans, which have a prominent postglenoid process and a squamotympanic fissure that takes a more posterior course that does not lie in the apex of the fossa. Some recent studies have suggested that the Ngandong and Sambungmacan hominids are not unique in their expression of these characteristics, and that they can also be found in other fossil crania from Africa and Indonesia. The present study reexamines these morphologies in an effort to better understand their distribution in the hominid fossil record. The results confirm that the lack of a prominent postglenoid process in combination with a squamotympanic fissure that lies wholly in the apex of the mandibular fossa along its entire length is indeed autapomorphic for the Ngandong and Sambungmacan fossils. This finding, in conjunction with work on other nonmetric features in these hominids, suggests that at least two hominid morphs, possibly representing separate species, were present on Java during the Pleistocene. In addition, if this apparent autapomorphy is confirmed, then it is also unlikely that the Ngandong hominids contributed to the gene pool of modern humans.

The morphological distinctiveness of Homo sapiens and its recognition in the fossil record: Clarifying the problem

AbstractSpecies are historically differentiated entities that, osteologically, may be differentiated to inconveniently varying extents. Living Homo sapiens is a distinctive morphological entity that is easily distinguished in both cranial and postcranial morphology from all other living hominoids and from the vast majority of its fossil relatives. In this contribution, we offer several apparent cranial apomorphies of the living species, while recognizing that it is reasonable to expect some degree of overlap in the ranges of variation of individual characters among closely related species such as those within the genus Homo. No one aspect of morphological detail may be considered totally diagnostic within very close‐knit groups of this sort or, conversely, be regarded as blurring the identities of their components. Overlap in morphological detail may even be expected in cases where striking Gestalt differences exist between closely related species due to major developmental reorganization. As a result, while the morphological and, by extension, historical distinction between such highly differentiated species pairs as Homo neanderthalensis and Homo sapiens is effectively unequivocal, in a nod to the intrinsic untidiness of biology the hominid fossil record does offer some instances that are much more difficult to interpret. In such cases, most, but not all, of the cranial apomorphies of living Homo sapiens, are present in individual fossil specimens or apparent populations. This is true, for example, of a set of variably dated and archeologically associated, as well as mostly incomplete, South African fossils (for example, Border Cave, Boskop, Fish Hoek, and most Klasies River Mouth specimens). These specimens very closely resemble living Homo sapiens in preserved overall cranial structure, but most conspicuously lack bipartite brows and fully developed human chin configurations. Whatever resolutions hominid systematists may reach in such cases, it is clear that to resort reflexively to such pernicious if convenient devices as “archaic Homo sapiens” only obscures any potential signals of systematic diversity in what is increasingly evidently a highly complex late Pleistocene hominid record.

A new species of great ape from the late Miocene epoch in Ethiopia

With the discovery of Ardipithecus, Orrorin and Sahelanthropus, our knowledge of hominid evolution before the emergence of Pliocene species of Australopithecus has significantly increased, extending the hominid fossil record back to at least 6 million years (Myr) ago. However, because of the dearth of fossil hominoid remains in sub-Saharan Africa spanning the period 12-7 Myr ago, nothing is known of the actual timing and mode of divergence of the African ape and hominid lineages. Most genomic-based studies suggest a late divergence date-5-6 Myr ago and 6-8 Myr ago for the human-chimp and human-gorilla splits, respectively-and some palaeontological and molecular analyses hypothesize a Eurasian origin of the African ape and hominid clade. We report here the discovery and recognition of a new species of great ape, Chororapithecus abyssinicus, from the 10-10.5-Myr-old deposits of the Chorora Formation at the southern margin of the Afar rift. To the best of our knowledge, these are the first fossils of a large-bodied Miocene ape from the African continent north of Kenya. They exhibit a gorilla-sized dentition that combines distinct shearing crests with thick enamel on its 'functional' side cusps. Visualization of the enamel-dentine junction by micro-computed tomography reveals shearing crest features that partly resemble the modern gorilla condition. These features represent genetically based structural modifications probably associated with an initial adaptation to a comparatively fibrous diet. The relatively flat cuspal enamel-dentine junction and thick enamel, however, suggest a concurrent adaptation to hard and/or abrasive food items. The combined evidence suggests that Chororapithecus may be a basal member of the gorilla clade, and that the latter exhibited some amount of adaptive and phyletic diversity at around 10-11 Myr ago.

Severe wear and tooth loss in wild ring-tailed lemurs ( Lemur catta): A function of feeding ecology, dental structure, and individual life history

The ring-tailed lemurs at Beza Mahafaly Special Reserve, Madagascar, exhibit a high frequency of severe wear and antemortem tooth loss. As part of a long-term study, we collected dental data on 83 living adult ring-tailed lemurs during 2003 and 2004. Among these individuals, 192 teeth were scored as absent. The most frequently missing tooth position is M1 (24%). As M1 is the first tooth to erupt, its high frequency of absence (primarily a result of wear) is not remarkable. However, the remaining pattern of tooth loss does not correlate with the sequence of eruption. We suggest that this pattern is a function of 1) feeding ecology, as hard, tough tamarind fruit is a key fallback food of ring-tailed lemurs living in gallery forests; 2) food processing, as tamarind fruit is primarily processed in the P3–M1 region of the mouth; and 3) tooth structure, as ring-tailed lemurs possess thin dental enamel. The incongruity between thin enamel and use of a hard, tough fallback food suggests that ring-tailed lemurs living in riverine gallery forests may rely on resources not used in the past. When comparing dental health in the same individuals ( n = 50) between 2003 and 2004, we found that individual tooth loss can show a rapid increase over the span of one year, increasing by as much as 20%. Despite this rapid loss, individuals are able to survive, sometimes benefiting from unintentional assistance from conspecifics, from which partially processed tamarind fruit is obtained. Although less frequent in this population, these longitudinal data also illustrate that ring-tailed lemurs lose teeth due to damage and disease, similar to other nonhuman primates. The relationship between tooth loss, feeding ecology, dental structure, and individual life history in this population has implications for interpreting behavior based on tooth loss in the hominid fossil record.

Interpreting the past: essays on human, primate, and mammal evolution in honor of David Pilbeam

This volume, published in honor of the occasion of David Pilbeam's 65th birthday, covers major topics in human, primate, and mammalian evolution, mostly from the Miocene to the present. The papers emphasize novel interpretations of several key areas of longstanding interest and importance, including Miocene biogeography and hominoid evolution, the origins of hominids, and new interpretations of the hominid fossil record. In terms of content, most of the papers tackle key issues in the evolution of hominoids and hominids in terms of systematic paleoenvironmental and behavioral questions. More broadly, however, the papers explore the epistemological problems of how one interprets the past from the available data.

The rise of the hominids as an adaptive shift in fallback foods: Plant underground storage organs (USOs) and australopith origins

We propose that a key change in the evolution of hominids from the last common ancestor shared with chimpanzees was the substitution of plant underground storage organs (USOs) for herbaceous vegetation as fallback foods. Four kinds of evidence support this hypothesis: (1) dental and masticatory adaptations of hominids in comparison with the African apes; (2) changes in australopith dentition in the fossil record; (3) paleoecological evidence for the expansion of USO-rich habitats in the late Miocene; and (4) the co-occurrence of hominid fossils with root-eating rodents. We suggest that some of the patterning in the early hominid fossil record, such as the existence of gracile and robust australopiths, may be understood in reference to this adaptive shift in the use of fallback foods. Our hypothesis implicates fallback foods as a critical limiting factor with far-reaching evolutionary effects. This complements the more common focus on adaptations to preferred foods, such as fruit and meat, in hominid evolution.

The effects of hybridization on growth allometry and craniofacial form in Sulawesi macaques

The present research investigates the effects of hybridization between Macaca maurus and M. tonkeana on adult male form and patterns of growth allometry. Comparisons of adult hybrid mean phenotypic values with the adult averages of the parental species indicate a condition of heterosis for cranial vault length and crown–rump length. Negative heterosis is indicated for body mass. Regression parameters describing growth allometry are generated for four craniofacial measurement variables and one body measurement using both least squares and reduced major axis regression. Comparisons of hybrid and parental regression slopes and intercepts using analysis of covariance and t-tests suggest that there is a hybrid pattern of growth allometry characterized by an increase in regression slope values coupled with lower intercept values compared to those of the parental species and the parental averages for most regression parameters. Multivariate analyses of the adult and ontogenetic morphometric data indicate significant differences across species taxa in form and shape during development and adulthood. Our finding of significant differences between hybrids and their parental taxa in growth allometry and craniofacial form and shape during development challenges the assumption often made regarding the reproductive and taxonomic significance of observed ontogenetic divergence between Neandertals and modern humans. We propose that anthropological primatology, with its goal of developing nonhuman primate models for investigating human evolution, can provide a biologically relevant means by which to empirically estimate the taxonomic significance of morphological and ontogenetic divergence observed in the hominid fossil record.

Role of Physical Anthropology in Intermediate and Secondary Education

The role of physical anthropology in precollegiate education has been limited, but has the potential to play a vital and integral role in promoting students' understanding of themselves and others. This study describes the development, implementation, and results of a program constructed on an inquiry-based learning model that introduces middle and high school students to the content of physical anthropology. Demonstrated student learning indicates that intermediate and secondary students are capable of acquiring and applying complex content about human evolution and diversity. Program findings indicate that students frequently had previous knowledge about the hominid fossil record but little information about the significance of human biological diversity. Teaching intermediate and high school students about our common evolutionary heritage and the fact that humans exhibit clinal variation were found to be both powerful and effective content material. The fact that program participants lacked previous knowledge about the relationship between human biological diversity (illustrated in this program by light and dark skin color) and the erroneous sociocultural construction of this diversity confirmed the suspicion that this content is not being addressed in precollegiate education. Traditionally, intermediate and secondary students are taught about human variation within the context of social studies, reading, communication, and fine-arts classes. This program identifies a new paradigm for teaching about human variation. Providing students with scientific knowledge about human origins and diversity provides a constructive starting point, creating a common platform and knowledge base on which to then frame discussions about cultural variation.

The Uninvited Skeleton at the Archaeological Table: The Crisis of Paleoanthropology in South Asia in the Twenty-first Century

Emerging from the philological-historical approaches of the eighteenth-century Orientalists, the scientific study of the hominid fossil record and prehistory of South Asia (India, Pakistan, Sri Lanka, and their borderlands) has a history of over two centuries. Today Western and South Asian scholars offer new answers to old questions about the origin and antiquity of the earliest hominids in the subcontinent, the beginnings of the Indus civilization, archaeological and skeletal interpretations about the reputed Indo-European-speaking Aryans of the Vedic tradition, biological affinities of ancient and modern populations, and palaeodemographic profiles of health and disease status, traumatic and developmental modifications, and population sizes and densities of earlier peoples in this part of Asia. At the beginning of the third millennium we respond to these issues in ways that modify or repudiate earlier theories and interpretations of archaeological and palaeontological data, e.g., a present-day recognition that hominids were present in the northwestern sector of the subcontinent during the geological period of the Pliocene-Pleistocene transition, the establishment of the roots of the Indus civilization in cultures established by 7000 B.C. and long before the period of the third millennium B.C. settlement and cultural diffusion, the fall of the Aryan migration myth and its racial and caste implications, and a reevaluation of population genetic affinities using DNA and more powerful statistical types of analysis of the skeletal record. This paper summarizes these and other recent advances in South Asian palaeoanthropology by noting transitions in scientific perspectives and present-day issues of research, and discusses prospects for the development of palaeoanthropology in South Asia at the dawn of the new millennium in the light of specific crises that will be encountered by its future practitioners.

Hypoglossal canal size in living hominoids and the evolution of human speech.

The relative size of the hypoglossal canal has been proposed as a useful diagnostic tool for the identification of human-like speech capabilities in the hominid fossil record. Relatively large hypoglossal canals (standardized to oral cavity size) were observed in humans and assumed to correspond to relatively large hypoglossal nerves, the cranial nerve that controls motor function of the tongue. It was suggested that the human pattern of tongue motor innervation and associated speech potential are very different from those of African apes and australopithecines; the modern human condition apparently appeared by the time of Middle Pleistocene Homo. A broader interspecific analysis of hypoglossal canal size in primates conducted in 1999 has rejected this diagnostic and inferences based upon it. In an attempt to resolve these differences of opinion, which we believe are based in part on biased size-adjustments and/or unwarranted assumptions, a new data set was collected and analyzed from 298 extant hominoid skulls, including orangutans, gorillas, chimpanzees, bonobos, siamang, gibbons, and modern humans. Data on the absolute size of the hypoglossal nerve itself were also gathered from a small sample of humans and chimpanzee cadavers. A scale-free index of relative hypoglossal canal size (RHCS) was computed as 100 x (hypoglossal canal area(0.5)/oral cavity volume(0.333)). No significant sexual dimorphism in RHCS was discovered in any species of living hominoid, but there are significant interspecific differences in both absolute and relative sizes of the hypoglossal canal. In absolute terms, humans possess significantly larger canals than any other species except gorillas, but there is considerable overlap with chimpanzees. Humans are also characterized by large values of RHCS, but gibbons possess an even larger average mean for this index; siamang and bonobos overlap appreciably with humans in RHCS. The value of RHCS in Australopithecus afarensis is well within both human and gibbon ranges, as are the indices computed for selected representatives of fossil Homo. Furthermore, the size of the hypoglossal nerve itself, expressed as the mass of nerve per millimeter of length, does not distinguish chimpanzees from modern humans. We conclude, therefore, that the relative size of the hypoglossal canal is neither a reliable nor sufficient predictor of human-like speech capabilities, and paleoanthropology still lacks a quantifiable, morphological diagnostic for when this capability finally emerged in the human career.

Identifying metameric variation in extant hominoid and fossil hominid mandibular molars.

Landmark data were collected from cross sections and occlusal images of mandibular molar crowns, and Euclidean distance matrix analysis (EDMA) was used to identify metameric morphological variation between the first and second mandibular molars of living taxa: Gorilla gorilla (n = 30), Pan troglodytes (n = 34), and Homo sapiens (n = 26). Two patterns of metameric variation were identified, one unique to humans and the other shared by chimpanzees and gorillas. In order to assess the utility of this type of analysis for the interpretation of the hominid fossil record, 19 mandibular molars from Sterkfontein Member 4, South Africa, were examined. The pattern of metameric variation of the Sterkfontein molars resembled that of the African great apes, and differed from the modern human pattern. These results demonstrate that data on metameric variation may provide information regarding function or developmental processes previously indiscernible from fossil material.

人類進化と新生代後期の環境変化 中新世末から鮮新世の化石人類 最近の動向

The past decade has seen an incredible amount of new hominid fossils recovered from the late Miocene and Pliocene of Africa. This paper reviews these discoveries. It is suggested that there exists little support for the often stated view of considerable phyletic diversity in the hominid fossil record.

The revolution that wasn't: a new interpretation of the origin of modern human behavior

Proponents of the model known as the “human revolution” claim that modern human behaviors arose suddenly, and nearly simultaneously, throughout the Old World ca.40–50ka. This fundamental behavioral shift is purported to signal a cognitive advance, a possible reorganization of the brain, and the origin of language. Because the earliest modern human fossils, Homo sapiens sensu stricto, are found in Africa and the adjacent region of the Levant at >100ka, the “human revolution” model creates a time lag between the appearance of anatomical modernity and perceived behavioral modernity, and creates the impression that the earliest modern Africans were behaviorally primitive. This view of events stems from a profound Eurocentric bias and a failure to appreciate the depth and breadth of the African archaeological record. In fact, many of the components of the “human revolution” claimed to appear at 40–50ka are found in the African Middle Stone Age tens of thousands of years earlier. These features include blade and microlithic technology, bone tools, increased geographic range, specialized hunting, the use of aquatic resources, long distance trade, systematic processing and use of pigment, and art and decoration. These items do not occur suddenly together as predicted by the “human revolution” model, but at sites that are widely separated in space and time. This suggests a gradual assembling of the package of modern human behaviors in Africa, and its later export to other regions of the Old World. The African Middle and early Late Pleistocene hominid fossil record is fairly continuous and in it can be recognized a number of probably distinct species that provide plausible ancestors for H. sapiens. The appearance of Middle Stone Age technology and the first signs of modern behavior coincide with the appearance of fossils that have been attributed to H. helmei, suggesting the behavior of H. helmei is distinct from that of earlier hominid species and quite similar to that of modern people. If on anatomical and behavioral grounds H. helmei is sunk into H. sapiens, the origin of our species is linked with the appearance of Middle Stone Age technology at 250–300ka.