Skeletal biologists are very much interested in learning how prehistoric peoples behaved and how various behaviors influenced their health. In the last two decades many skeletal experts have identified this approach with the term bioarchaeology, the use of which actually dates back to the 1970s (Buikstra, 1977). In current practice, most bioarchaeologists use a broad-based approach (Buzon, 2012). There are, however, some researchers who regard bioarchaeology from a more limited perspective, especially where attempts are made to reconstruct activity patterns in the past (Jurmain, 1999).
Reconstructing Prehistoric Activities
Understanding what sorts of activities ancient peoples practiced is obviously a fascinating area of research. Can we learn about specific activities from skeletons? The answer is that sometimes it’s possible but frequently it isn’t. The ways in which bone responds to activity (and other influences) involve complex physiological and biochemical processes and are best approached using rigorous scientific methods. Thus the study of evidence of activity in skeletons provides a good example of hypothesis testing and verification.
Three different types of skeletal changes have been especially popular with bioarchaeologists attempting to reconstruct prehistoric activities: osteoarthritis, areas where muscles attach to bones, and bone geometry (i.e., bone shape). Osteoarthritis (OA) is a very common condition seen in all human populations. A simple conclusion that is frequently made assumes that osteoarthritis results mainly from activity; following this logic, people who work harder should end up with more OA in their skeletons. Think about this interpretation as a hypothesis. Let’s say we see more OA in the skeletons of some individuals than others in an ancient population. Did those with OA work harder? Did they participate in some particular activity that increased the amount of arthritic bone change? The answer may be “yes,” but most likely it’s “no.” The safest conclusion is that we really cannot say. The problem arises because we know from biomedical research (including thousands of published studies) that OA is caused by structural and biochemical changes to the cartilage at the ends of bones and that these changes are primarily caused by advancing age, genetic influences (varying considerably among individuals), and possibly previous injury. Because of the importance of age as a contributing factor to the development of OA, any comparison between groups must first consider age differences between them. If one group is primarily composed of younger individuals, then the prevalence of OA should be lower than it would be in a group composed mainly of older ones. Also, comparisons among groups require statistical testing, and this fact dictates that samples should be large enough for tests to be valid.
Many bio archaeologists assume that OA (and other bone changes discussed below) results from regular adult activities such as climbing, carrying heavy loads, grinding grain, etc. But once we consider particularly the influences of age and genes, there is vey little remaining evidence to suggest that activity was the main cause of arthritic bone changes (Fig. 15-20). There are, however, a few exceptions. For example, elbow arthritis in Eskimo (Inuit) skeletons likely reflect, at least in part, extreme activities (Merbs, 1983; Jurmain, 1999).
Another type of skeletal change that has been related to specific activities is alterations to the areas where muscles attach to bones. In this type of research the basic assumption seems clear. That is, increased activity that repeatedly uses certain muscles produces changes to points of attachment. This certainly can be the case for acute injury (such as a torn muscle). But what can we say about more typical long-term adult activities? Once again, evidence from medical research indicates that the causes of such bone changes are numerous and include age and genetic influences (Milella et al., 2012).
One very useful way to test hypotheses and help control for these various influences (which medical experts call“confounders”) is through investigation of contemporary skeletal collections where age and sex are known.* Research of this kind has helped to standardize methods, test specific hypotheses, and demonstrate that the underlying biological influences on muscle attachment sites are complex (Alves Cardoso and Henderson, 2010; Milella et al., 2012; Jurmain et al., 2012). Study of bone geometry is the third method that can potentially shed light on prehistoric activities. This approach has tended to be more biomedically oriented than the others discussed so far and has also been more successful in testing hypotheses. In particular, a study of student athletes at Cambridge University compared with a set of nonathletes provided strong confirmation that certain types of very strenuous activities can alter bone geometry (that is, the shape and strength of the bone) (Shaw and Stock, 2009a, b).
Reconstructing Prehistoric Diets
Skeletal biologists also study prehistoric diets. In the last several years chemical techniques have been developed that provide good information about what people were eating in the past. Stable isotope analysis has proven to be a very useful way to reconstruct the diets of ancient humans and has become widely used. As discussed in Chapter 9, stable isotopes are different versions are vital to life. Squamous cell carcinoma (Scc) of the same element that vary in their structure (that is, in their atomic weight). For example, carbon has two stable isotopes, ¹³C and ¹²C, which differ in atomic weight. Humans incorporate different amounts of these isotopes into their tissues from foods that vary in isotopic composition. Stable isotopes in teeth specifically record childhood diet, and they do not change after they are formed; in adul stress In a physiological context ts, isotopic analysis of the organic and mineral content of bone provides a record of diet over the last several years of life.
Stable carbon and nitrogen isotope analyses of human bone provide the most information about diet. Carbon isotope ratios in plants vary based on one of three possible chemical pathways; these ratios are incorporated into the bones and teeth of the people who ate these foods. In addition, marine organisms (for example, fish and sea mammals) have isotope ratios that differ from those of most terrestrial plants and animals. Stable nitrogen isotope ratios provide another source of information on diet. Plants typically have the lowest nitrogen isotope ratios, and these ratios increase in animals at each higher level in the food chain. Analysis of carbon and nitrogen isotopes together helps not only to identify the source of food (for example, marine or terrestrial), but can also indicate the general position of human societies within a local food web.
For example, stable carbon and nitrogen isotope analysis has revealed that early prehistoric Native Americans from the San Francisco Bay area ate significant amounts of salmon and marine mammals, which are near the top of the food chain. However, later in time, bone isotope ratios record a change in diet toward greater consumption of land animals and plant foods (for example, deer and acorns). These changes in diet may reflect increasing resource stress associated with population growth in the region (Bartelink, 2009).