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This text was drafted by award-winning MMW TAs Tara Carter and Beth Peterson, (Anthropology) in the summer of 2008, supported by the MMW-based research funds left in his account on the death of Prof. Donald F. Tuzin, long an instructor and supporter of MMW. The text was substantially modified by Professor David K. Jordan in summer, 2011 to fit it to the needs of MMW-11.
This text may be freely reproduced for non-commercial educational purposes.
The study of prehistoric humans and animals arose when people stumbled across their remains, or sometimes their artifacts, and realized that they were different from forms that walk the earth today. Although the differences can be interesting in themselves, what is of most concern, of course, is how prehistoric creatures actually behaved, and the evolutionary forces that shaped that behavior and, in the case of pre-human forms, that may have shaped our own behavior. Questions about behavior are difficult to answer from the physical remains, sometimes derogatorily dismissed as mere “stones and bones”
Reconstructing prehistoric behavior, and especially the behavior of our hominid ancestors, is one of the major goals of both biological anthropology and prehistoric archaeology. This essay will discuss the ways in which specialists approach the analysis of the physical remains of prehistoric hominids.
Our main data are fossilized skeletal remains. The term “fossil” can refer to a bone, a shell, or even the impression of a plant or animal which has been preserved in rock for a very long time.
Most fossils are stone. Basically, over a long period of time after death, the tissue of a hominid bone, for example, gets replaced with minerals leaching into it from the surrounding soil, creating something that still has the shape of a bone, but is now really a stone.
Fossilization is quite handy for our investigation into our hominid history, but unfortunately it rarely happens, so fossils are hard to find; even when we do find them, we never find a complete fossilized skeleton. Furthermore, usually only the harder, denser bone lasts long enough to undergo the fossilizing process. Teeth, jaws, and some of the limb bones are the most common. Other, softer bones often decay into dust, as of course do the yet softer tissues of skin, muscle, or internal organs. Fossils, in sort, provide us with a very incomplete impression of the original individual, and collectively they provide a very poor picture of a population. So how, exactly, can we coax these silent fossils to tell us anything about behavior?
Biological anthropologists can indirectly study hominid behavior through a variety of avenues, including:
By collecting data in each of these areas, specialists can construct models that help us understand what kinds of social groups our hominid ancestors probably lived in, what they probably ate, how they probably got their food, and even what kinds of cognitive abilities they probably possessed.
There are admittedly a lot of “probablies” in that sentence. That means we are never 100% certain that new data or new modes of analysis may not change the picture. But it also means that we are making a reasonable reconstruction and not an arbitrary one, and that our models take the most reasonable account we can of whatever data are available. (A separate essay discusses models. Briefly, a model is a description of a process, including its parts and their relationships, including causal relationships. )
To make these models, anthropologists rely on the “scientific method,” which allows them to come up with a particular argument for hominid behavior. “Scientific method” is not merely a grandiose name. It refers to a logical and disciplined approach to both problems and data. Accordingly, before we can get into what these models are all about, we should first review what the scientific method is and how in influences the way in which an argument can be crafted.
There are many different ways that human beings have attempted to explain the world around them, including religion, storytelling, imagination, and science. Science approaches the world by generating hypotheses (hunches) about how something works, and then testing them, that is, trying to find ways to show that they are wrong. Obviously, it is applicable only to hunches for which a possible test can be devised.
The scientific method is the basic process of science, and as a process is takes a researcher through a series of steps.
Believe it or not, arguments follow a fairly standard formula:
You must have both facts and an interpretation of those facts to make argument. Otherwise, if you only state the facts then you are reporting or describing, not arguing,. And if you only give interpretations with no facts to back anything up, no one can truly evaluate your claim, and it is merely an unpersuasive assertion. (By the way, the formula works well not just in scientific investigations, but also in writing term papers and exams. Hint, hint!)
While this all seems fairly straightforward, we are sorry to report that sometimes it is difficult to know what is a fact and what is an interpretation. Facts are data: they are observable realities of the world around us. For example, it is a fact that there are dogs and cats living in La Jolla. Interpretations of facts are used to create a theory. A theory is a broad, generalized framework that makes sense of facts and can be tested against evidence. One theory might be that dogs make better swimmers than cats. A good rule of thumb is to ask yourself, “could anyone disagree with this statement?” If they can, then it is probably your interpretation or theory. If no one could disagree with you, then it is probably a fact.
With these tools in mind, we are now ready to take a look at how anthropologists can make fossils talk.
Studying the behavior of living primates is one of the most important tools we have for reconstructing hominid behavior because they are our closest living relatives. While Western philosophy has traditionally drawn a stark line separating humans from animals, it is important to remember that human beings are animals, too, and that the same natural and ecological forces that act on other animals act on us. Primatologists are researchers who study living non-human primate behavior with the explicit goals of reconstructing hominid behavior and understanding modern human behavior. Many primatologists are anthropologists, but they are also found in psychology and biology departments.
Behavioral Ecology. Most primatologists today study primates from a perspective known as “behavioral ecology.” Behavioral ecology is the study of the relationship between behavior, the ecological environment, and biological organisms. When it introduces the element of time, it is the study of the evolution of behavior that emphasizes the role of ecological factors as agents of natural selection. The behaviors and behavioral patterns that are exhibited by animals in the world today are a result of natural selection; they have been selected because they increase the reproductive success of individuals.
There are many misunderstandings about behavioral ecology and what it means to study the evolution of human behavior from this framework. Behavioral ecology does not make explicit claims about the relationship between genes and behavior; other fields such as behavioral genetics, try to learn more about that. The relationship between genetics and behavior is not very well understood, and for most animals there is not a simple one-to-one relationship between genes and behavior. In most insects and other invertebrates, behavior is largely controlled by genes, but in vertebrates such as birds and mammals, much behavior is learned and not under the direct control of genes.
Behavior is a complex and dynamic trait that emerges out of the interaction between genes and the environment, and the environment includes not only the physical world but also other species and other members of one’s own species. Among different animal species there is a great deal of variation in how much behavior is learned and how much flexibility an animal has in responding to different circumstances (a trait known as “plasticity”). Genes are, of course, extremely important in shaping an organism; they can be thought of as a limiting factor for behavior. Genes set the boundaries for the learning potential of a species or individual. But the developmental process plays an equally essential role in shaping an individual organism. Humans have very plastic behavior, but so do other primates, who have to learn how to be successful members of their species. This is one of the reasons that primate models are so important in studying human evolution —we can look at how they live and respond to the problems presented to them in order to gain an understanding about how our fossil ancestors might have solved similar problems.
Non-human primates are good candidates for modeling human evolution because they are our closest living relatives. Because of our close genetic relationship, many researchers argue that there must also be similarities in our behavior. We share 95-98% of our genetic material with chimpanzees and bonobos. That does not mean that chimpanzees or bonobos will give us all of the answers about human evolution. After all, there have been about 5 million years since our last common ancestor with chimps and bonobos, and we have all done a lot of evolving since then. Today’s bonobos and chimps are adapted to different social and physical environments than our ancestors were, and so are we.
But we shared a common ancestor with chimps and bonobos, meaning that some of what they do and some of what we do has a common origin. In the behavior of chimps and bonobos (and other primates) we can see some striking similarities with our own behavior. For example, most primates have a long period of infantile dependence, both physical and psychological, on their mothers, when they not only are nourished by food from their mothers but also learn a great deal about how to be a successful primate. Chimpanzees are accomplished tool makers and tool users, using tools to fish for ants and termites (modified sticks), crack open palm nuts (stone hammer and anvil), and sponge up water (chewed up leaves). What primatologists look for in studying primates are these kinds of behavioral patterns and the selective pressures that may have led to the evolution of those patterns.
An example of a comparative study of humans and chimps is provided as Appendix 2 in this set of essays.
For many of the same reasons that we study primate behavior to learn more about the evolution of human behavior, it is important to study primate (and other animal) anatomy in order to understand the evolution of human anatomy and how it relates to behavior. The link between anatomy and behavior may not be apparent on first blush, but if we think about the fact that all of our behavior is constrained by the form and function of our bodies, we can see how the way our bodies are put together has a big impact on how we behave. For example:
If we study anatomy across living species and apply that knowledge to understanding the behavior of forms represented by fossils, we can examine how different primate species are put together anatomically and how that influences their behavior. Baboons are quadrupedal (walk on for legs). This influences how fast they can run, what positions their body can be in when they sit or stand, how they process food, and how they engage in social interactions from friendly grooming to fighting. Chimpanzees are knuckle-walkers, meaning that they walk on their back feet while leaning on the outer surface of the middle fingers on their hands. Somewhere in our evolutionary history, we went from a chimpanzee-like knuckle-walking animal to a bipedal animal and the only way to study when this monumental event occurred in human evolution is to study the fossil record. Understanding how bones are put together in quadrupedal, knuckle-walking primates in contrast to bipedal primates, we can look at the fossil record to discover when the skeletal characteristics of fossil hominids became bipedal. It is only by knowing how the different bones fit together and what that means for range of motion in joints or how ligaments attach bones to muscles that we can reconstruct the locomotor (movement) behavior of fossils.
Research update (110920): The above paragraph should have been revised when this article went to press in the Soucebook, but was somehow missed. The latest research strongly suggests that no human ancestor was a knuckle-walker, but rather that knuckle-walking probably evolved in the non-human primate line after the separation of the line that led to us from the line that led to modern apes. For a picture, see the glossary of the Essential Fossils collection. (Direct link)
When archaeologists find stone tools or other artifacts during excavations, it is often difficult to determine what they were or what they would have been for. Archaeologists have to use the scientific method to generate and test hypotheses about the construction and function of tools. Experimental archaeology attempts to reconstruct the process that produced the artifacts that archaeologists study in order to understand how artifacts were made, how they were used, and who constructed them. In other words, we pretend to be prehistoric, making tools, gathering and processing plant material, hunting and butchering animals, and building houses using the same materials and processes used by fossil hominids. It can be fun, of course, but it is not a game. The goal is to discover all we can about the behavior and cognitive capacity of our fossil ancestors. Experimental archaeology, sometimes called “middle range research,” can help
Flint knapping is a type of experimental archeology where researchers produce stone tools that are the same as stone tools in the fossil record. Not surprisingly, there is nothing quite like trying to butcher an animal with a chipped stone tool to discover that some kinds of stone or some kinds of chipping are more appropriate to the task than others. If a flint knapper can produce a flake identical in design and structure to an artifact, we can be pretty sure that the same process produced both tools. But there is another aspect to flint knapping. Stone is not indestructible, and just as it can be chipped, it can also be abraded, and the actual use of a stone blade, say, produces microscopic scarring along the cutting edge. When stone tools are used in different activities, such as cutting deer meat from the bone, different types of abrasion occur. By comparing wear patterns from prehistoric artifacts with imitations produced through modern flint knapping, archaeologists can test hypotheses about how the prehistoric tools were used.
Taphonomy is the study of burials and of how organisms decompose over time. Since the principle of uniformitarianism (of which more in Essay 3) states that the natural forces that affect the earth today operated the same way in the past, taphonomists can reconstruct the process of decomposition and fossilization, thus providing essential contextual information about fossil and artifactual deposits. There are, of course, any number of ways a hominid ancestor could have died —disease, predation, or injury— and, if researchers are lucky, evidence of the cause of death may remain.
For example, say a prehistoric hominid female was out one day getting a drink of water by a stream and was attacked and killed by a giant hyena. The killing and chewing by the hyena would leave distinct marks on the bones of the hominid that would remain after death. Once she was dead and the hyenas were done eating, decomposition would begin with scavengers, insects, microorganisms coming along and doing their jobs, accelerating the decay of the hominid. Over time, all that would remain of the hominid would be her bones.
Over time, her bones would come to be covered by soil, perhaps trampled by a herd of boars, and maybe even moved downstream and buried under sediment from a flood after heavy rains. Half a million years later, parts of the skeleton might be discovered by anthropologists excavating the ancient stream. Based on the marks left on the bones, the breakage patterns, and their arrangement and context in the deposit, the anthropologists might be able to determine the cause of death and even that she was washed downstream (because some of the soil surrounding her would be similar to the soil upstream where she died and not where she was eventually deposited).
This is hypothetical. A real-life example of taphonomy in action is available as Appendix 3 in this set of essays. (Link)
In summary, the study of prehistoric hominid behavior is difficult and often frustrating, and many of the questions we most want to ask can’t be formulated in ways for which evidence is available. But by the constant formulation of hypotheses, the repetitive testing of them, and the incorporation of the results into ever more comprehensive models, scientists have been able to create a probabilistic model of hominid behavioral evolution that is ever more convincing.
The following review quizzes are available for this reading:
Essay 1 Quiz
Wimp Version (1), Wimp Version (2),
Hero Version.
The hero version contains all the questions from both wimp versions, combined into a single quiz.