A Companion to Paleoanthropology

David R. Begun, David R. Begun

• Publisher: Wiley-Blackwell
• Year: 2012
• ISBN:
  9781118332375
• Edition: 1
• Topic: Social Sciences
• Subtopic: Physical Anthropology
• Index: Social Sciences

A Companion to Paleoanthropology presents a compendium of readings from leading scholars in the field that define our current knowledge of the major discoveries and developments in human origins and human evolution, tracing the fossil record from primate and hominid origins to the dispersal of modern humans across the globe.

• Represents an accessible state-of-the-art summary of the entire field of paleoanthropology, with an overview of hominid taxonomy
• Features articles on the key discoveries in ape and human evolution, in cranial, postcranial and brain evolution, growth and development
• Surveys the breadth of the paleontological record from primate origins to modern humans
• Highlights the unique methods and techniques of paleoanthropology, including dating and ecological methods, and use of living primate date to reconstruct behavior in fossil apes and humans

CHAPTER 1

The Past, Present and Future of Paleoanthropology

David R. Begun

Paleoanthropology is the study of human evolution and that of our closest living relatives, the other primates. Humans of course are primates, and paleoanthropologists recognize the importance of understanding primate evolution as a necessary condition to understanding human evolution. This is the reason primate evolution is most commonly considered a part of paleoanthropology as opposed to the larger field of vertebrate paleontology. Paleoanthropology also includes a variety of other fields that tremendously inform the study of paleoanthropology. These include primate biology, systematics, ecology, genetics and geology. And of course, since paleoanthropologists are interested in the behavior of fossil humans, and since many of these humans left material evidence of their behavior in the fossil record, the analysis of this record, Paleolithic archeology, is also a major part of paleoanthropology. Because the material evidence of the behavior of fossil humans is so ubiquitous, while it is essentially non-existent in other animals, paleoanthropology is unique among the historical sciences.

The chapters in this book are organized around the themes that represent major areas of research in paleoanthropology. After an introductory chapter on the history of paleoanthropology, the first section of the book is on method and theory (experimental approaches, quantitative methods and life history theory). The second section on individual anatomical regions includes reviews of the evolution of the skull, brain, dentition and diet, and the limbs. The third section is devoted to environment and behavior, and includes chapters on paleoecology, geochronology, the reconstruction of social behavior using primate models, and Paleolithic archeology. In the fourth ­section, on genetics and race, there are chapters on the genetics of primate evolution and the genetic determinants of morphology, as well as a chapter on the race concept historically and today in paleoanthropology. The final three sections of the book ­consist of chapters describing the fossil evidence of primate evolution from their ­origins through the Quaternary period to the emergence of modern humans.

The history of paleoanthropology, in the sense of a general interest in understanding where we came from and how we fit within, or what our role is in the known world, is quite ancient, but the science of paleoanthropology is relatively recent (Goodrum, Chapter 2). At the end of the 18th century and especially in the first half of the 19th century, ideas of the antiquity of the earth (geologic time), transformationism (evolution), comparative anatomy and even the precursors of structural biology (unity of plan) were contributing to a new vision of natural history (or natural philosophy). For some time before that explorers brought back with them from exotic locals animals that looked strangely human-like, and our knowledge of these creatures (non-human primates) increased considerably in the 19th century. By the second half of the 19th century, Darwin had published on natural selection and human evolution, Huxley had documented the anatomical similarities between apes and humans, Mendel had discovered the basic principles of genetics, and early archeologists were beginning to amass impressive collections of artifacts of apparently great antiquity.

The first practitioners of paleoanthropology were comparative anatomists, archeologists and people willing to explore the far-reaching corners of the world in search of evidence of human evolution. The first of these were not trained in paleontology and were most commonly anatomists or physicians. Beginning in the 19th century and well into the first half of the 20th century, researchers explored the habitats of living primates, and over the years they also “harvested” vast numbers of primates. Although it has been a long time since this practice was repudiated by researchers (except in special cases such as culling), the resulting collections are among the most valuable resources of comparative data for paleoanthropologists. These same researchers began to document the behavior of primates in their natural habitats.

During the 20th century the disciplines of archeology, comparative anatomy and primatology, and fossil-collecting techniques, became more refined and sophisticated. Experimental approaches appear in the 1940s and 1950s, exploring the functional anatomy of the musculo-skeletal system and the behavior of primates in captivity. Our knowledge of genetics exploded following the discovery of heritable material (chromosomes) in cells in the beginning of the 20th century. Researchers began to embrace the idea of combining all of these approaches into the unified discipline of paleoanthropology, and by the 1970s it became increasing routine for paleoanthropological projects to combine the collection of fossils with archeology, geology, paleoecology (developed from vertebrate paleontology) in the field, and comparative anatomy and experimental biology in the lab.

The first chapter of the section on method and theory is on systematics (Strait, Chapter 3). Though limited to hominin systematics, this chapter makes it clear that there is much disagreement among researchers on the precise pattern of relationships among hominins, and even disagreement on what to call this group.¹ As Strait says, the words consensus and paleoanthropology are rarely used in the same sentence. While I am a bit less pessimistic, and see more consensus now than ten years ago, we have a very long way to go before we have the fossils and the analyses of them necessary to fully resolve the mysteries of the human fossil record. And this does not even include debate about the primate fossil record, which is at least as contentious. Although it would be satisfying to have all the answers, this would put many of us out of business. Actually, science does not work that way. There is always uncertainty in science, but in the historical sciences it is a real challenge to make convincing cases for events that occurred well before anyone who ever lived could have witnessed them. To me, that is precisely what makes paleoanthropology so exciting.

One clear pattern that emerges from an analysis of the human fossil record is that it is very complex. No one today would hold, as in the past, that humans evolved as a single lineage from a chimp-like ancestor to modern humans. It is clear that there are many branches, most of which were dead ends, experiments in being bipedal. Given the number of false starts, it is very difficult to know which among these early bipeds led to modern humans. In fact, we do not even know if any of the known fossil hominins are directly related to modern humans, and I would argue that there is a good chance that none of them are. But one of the known early hominins is probably more closely related to the genus Homo than are the others. Deciding which one is the best candidate is going to take some more time.

Another clear aspect of the study of hominid systematics is the nearly universal application of the principles of cladistics analysis (Strait, Chapter 3). While there remain some detractors, the majority of researchers recognize the value of cladistic methodology in revealing patterns of evolutionary change.

The next chapter in the methods section describes experimental approaches in paleoanthropology (Ravosa, Congdon and Menegaz, Chapter 4). Since Washburn called out to biological anthropologists, in the middle of the last century, to incorporate more experimental research, lab research has developed as a major aspect of paleoanthropology. Much of this involves testing hypotheses of muscle recruitment or the nature and magnitude of strains produced by various activities, whether dietary or locomotor, which serve ultimately to test ideas of selection pressures for certain changes observed in the fossil record. Experimental research tests ideas such as “­powerful brow ridges are a response to powerfully chewing: false”; “mandibular morphology responds in predictable ways to diet and the mechanical properties of food: true”. Experimental approaches have allowed us to test in repeatable ways many mechanical implications that emerge from speculations ranging from the origins of bipedalism to the manufacturing of stone tools.

Chapter 5 in the method and theory section is devoted to a review of commonly applied methods of quantitative analysis in paleoanthropology (Schillaci and Gunz, Chapter 5). While multivariate methods have been applied to paleoanthropological questions for years, they are now more or less de rigueur. The authors divide their chapter into multivariate techniques used to analyze traditional (linear or angular) data and techniques for geometric morphometric data. The latter has experienced an explosion in popularity. Many researchers, myself included, have some difficulty understanding the assumptions and limitations of many of these methods, and this chapter serves to clarify some of these mysteries.

The final chapter in this section is on life history, growth and development (Kelley and Bolter, Chapter 6). The importance of these issues in interpreting the hominid fossil record has also expanded greatly in recent years, mainly, I think, due to the development of techniques to assess patterns of growth and development, especially in the dentition. Major developments in life-history research based on the fossil record have led to the recognition that the earliest hominins grew much more like great apes than humans, and that even more recent fossil humans, such as Homo erectus and Neandertals² differ from modern humans. It is clear that researchers are increasingly interested in understanding the life history of the fossil taxa they study, and that growth and development are significant if not the major processes that contribute to evolutionary change.

The next section of this book explores the evolution of various regions of the body. Shea (Chapter 7) reviews what we know about the evolution of the cranium in hominoids. He makes the important point that more needs to be done to understand the nature of the hylobatid (gibbons and siamangs) cranium and how it informs us about the evolution of the cranium in the hominids (great apes and humans). There is a tremendous range in the body mass of hominoids, with the smallest ones (gibbons) on average about 30–35 times smaller than the largest ones (male gorillas). This makes it a challenge to compare hominoid crania, as the effects of size must be accounted for. The range of variation in morphology is also spectacular, especially when fossil hominoids are included. In addition to diet and brain size, which are the most common mechanical constraints thought to mold the cranium, allometry (size and shape relationships), sexual dimorphism and other aspects of social adaptation need to be incorporated into analyses of cranial morphology.

Chapter 8 (Schoenemann) is a review of the evidence of the evolution of the hominid brain. Brains are of obvious interest in paleoanthropology given the remarkable size of the human brain. This needs explaining, but this endeavor is complicated by the fact that the brain is an extremely expensive and very poorly understood organ and that it is not preserved in the fossil record. We have the general sense that the bigger the brain, the “brainier” the species, but we also know that diversity in brain size within a species is not correlated to intelligence. It is well known that there is no correlation between intelligence and brain size in humans, the latter of which varies in normal individuals by a ratio of 1 : 2 (roughly 1000 cc to 2000 cc). The causes and consequences of brain size increase in the human lineage is a fascinating area of study. New techniques of analysis of fossils, such as high-­resolution CT imaging, and a deeper understanding of the function of the brain will help us to understand more completely the reasons behind the spectacular ­evolution of the human brain.

Chapter 9 (Ungar and Sponheimer) focuses on research related to reconstructing the diet of our fossil ancestors, based on the anatomy of the jaws and teeth and from the dueling perspectives of the effects of the mechanical properties of food on our teeth and the chemical signals left behind by the foods we eat. All mammals, which have complex teeth and complicated dentitions, have evolved tooth forms that serve them well in processing the foods they normally eat (or they would not survive). Thus, tooth form is strongly related to broad aspects of diet, such as whether an organism routinely crushes hard or tough foods, slices through fibrous foods, or grinds more pulpy foods. Even the histology of teeth (the internal organization of cells and molecules that make up the tooth) affect the way a tooth responds to strains, and this can also be used to reconstruct diet in our ancestors. Moving away from structure, the chemical composition of teeth (and bone) reflects the aphorism that you are what you eat. There are numerous chemical indicators of diet that can be recovered from fossils. In addition, of course, what we find at sites with fossil hominins (and in some cases other fossil primates) tells us something about what they ate, whether it is the plant or animal remains found with them, food residue on their teeth or stone tools, or a general understanding of the ecology of the places in which they lived.

Chapter 10 reviews the evolution of the postcranial skeleton from apes to humans. The goal here is to, firstly, set the stage for the evolution of bipedalism by discussing the evolution of the trunk and limbs in fossil apes, and then to survey major transformations in the postcranium of hominins. It is almost universally agreed that humans evolved from a suspensory ancestor. There are a large number of features of the skeleton of apes and humans that are unique, and plausibly related to suspensory behaviors (hanging below the branches of trees). These features develop gradually from more monkey-like anatomy in the earliest apes (pronograde quadrupedalism, or walking on the tops of branches), to an essentially modern ape morphology in the apes that lived just before the chimpanzee–human divergence. While the wonderfully complex fossil record of apes shows that many similar looking anatomies evolved in parallel a number of times, there is no doubt that there is a consistent trend toward a shift from monkey-like to ape-like in the plausible ancestors of the living apes and humans. By 6–7 Ma (mega-annum, or millions of years ago), fossils representing taxa with some, as yet unknown, form of human bipedalism are known from Africa, and by 6–4 Ma these evolve into Ardipithecus, with a curious mixture of bipedal and climbing characters (Simpson, Chapter 22). The transition to modern human postcranial form, however, is reasonably well documented in the fossil record from Australopithecus to Homo erectus (Hammond and Ward, Chapter 23; Antón, Chapter 26). After Homo erectus, the changes in the postcranium leading to modern humans are more or less fine-tuning, though there are important differences, especially between fossil Homo and modern humans, who are essentially domesticated (wimpy and less robust) versions of our ancestors, as far as our skeletons go.

Chapter 11 introduces the next section of the book, on environment and behavior. Though behavior is discussed in other chapters, here we are looking mainly at data from fields outside of morphology. The first chapter, by Reed, covers the rich and highly informative field of paleoecology. As Reed describes it, modern paleoecology takes a multiproxy approach that applies as many sources of information as possible to reconstruct the paleoecology of fossil localities. These include comparisons of species composition with modern communities and distributions of adaptations present in a site, regardless of species composition (running, digging, climbing, diet, etc.), known as ecomorphology. They also include evidence from the sediments in which fossils are found, the landscapes in which sites are found, and the chemicals (isotopes) found in both the sediments and the fossils themselves. Paleoecologists also employ information from larger-scale processes such as orogeny (mountain-building), glaciation and continental drift. A paleoecological analysis of a fossil locality would not be complete without an understanding of its taphonomy, that is, a reconstruction of the circumstances by which the fossils found in a spot came to be deposited there. Sometimes it is because the organisms died in that spot, but many times it is because their remains were transported, most commonly by water, from more distant spots. It is the taphonomist’s job to determine to what extent the assemblages of organisms at a site are autochthonous (local and representing a moment in time) or allochthonous (mixed, both in time and space).

Chapter 12 (Plavcan) tackles the challenging topic of reconstructing social behavior from the fossil record. Social behavior has been implicated in everything from basic survival to brain-size increase and the emergence of culture and language. There have always been speculations about the evolution of these features of humans and this chapter describes the limitations of the evidence and the extent to which a rigorous approach can reveal very interesting patterns. As with paleoecology, the ­reconstruction of behavior uses the approach of analogy to living species, with the idea that if patterns of, for example, sexual dimorphism in body mass or canine size, are the same in a sample of fossils of a particular taxon and a living taxon, a reasonable hypothesis is that the living and extinct species share aspects of their social behavior related to sexual dimorphism (sex ratios, relations within and between the sexes, care of infants, etc.). Other morphological features implicated in the reconstruction of behavior (other than diet and positional behavior) include brain size and orbital dimensions (nocturnal primates have larger eye sockets on average). There are many caveats to reconstructing behavior from the fossil record when there lacks a direct mechanical explanation linking behavior and anatomy (like powerfully built jaws and powerful chewing), but this does not make it less worthwhile or important. Consider how much we have learned about dinosaurs from the discovery of their nests and grouping patterns and the surprising insights this has provided about their strategies for rearing their young. The advances in reconstructing social behavior in primates and humans is at least an order of magnitude more advanced, but also more complicated.

Chapter 13 (Deino) covers the world of geochronology as applied to paleoanthropology. Geochronology is simply the telling of time using data preserved in the geological record, including rocks and fossils (which actually are also rocks). The age of fossils is one of the most sought after pieces of information about them, even if it is sometimes misinterpreted. There is no doubt that we need to place fossils in a chronological sequence to understand the evolution of a lineage, but the fact that a fossil taxon from a particular site may be older than another from another site does not necessarily mean that the fossil taxa actually evolved in that order. In other words, we cannot assume that the ages of fossils represent the actual origins and extinctions of species. We call the order of appearance of fossil species in the fossil record first and last occurrences, meaning the oldest and youngest known ages, to distinguish from their real biological origin and extinction, which are basically unknowab...

Table of contents

• Cover
• Series page
• Title page
• Copyright page
• List of Illustrations
• List of Tables
• Notes on Contributors
• Acknowledgments
• CHAPTER 1: The Past, Present and Future of Paleoanthropology
• CHAPTER 2: History
• PART I: Background to Paleoanthropology
• PART II: The Fossil Record
• Index