Adaptation in Archaeology
The theory of evolution is inherently attractive for archaeologists, who are concerned with the long-term history of humankind (Dunnell 1980). Changes through time during the long process of hominization are, by definition, adaptive. Adaptation is clearly one basic constituent of evolution. For that reason, the concept of adaptation – including the capacity for a cultural system to adjust to changes – is important in many approaches, particularly in ecologically oriented archaeology and, more recently, in evolutionary archaeology.
Basically, adaptation refers to “the idea that organisms are fitted for the particular environments in which they live” (Alexander 1962: 826) or more directly to the “conformity between the organism and its environment” (Pianka 1983: 85).
It is accepted that an adaptation refers to both the state of being adapted and the process that produces the adaptation. However, even biologists have found it difficult to recognize adaptations, and the acceptance that natural selection is not the only mechanism behind evolutionary processes was one result of this difficulty (Vrba and Eldredge 1984).
The concept of adaptation used by many archaeologists was based on the work of classic evolutionary anthropologists like Leslie White (1949) and Julian Steward (1955). In these approaches, tools are seen basically as extrasomatic means of adaptation. The assignation of functions to archaeological tools and features is the key concept to understand and discuss adaptations, an activity that falls within the approach known as cultural evolution, which is extremely popular. Circularity is the main interpretative problem of this approach. Effectively, the role of adaptation as an ex post facto argument invoked as the cause of both the appearance and the persistence of archaeological traits was and is an impediment in most applications (O’Brien and Holland 1992).
On a slightly different vein, Patrick Kirch wrote about “the continuous modification of … behavioral patterns in response to changing environments, by means of selective retention of behavior” (Kirch 1980: 110). He explained that it is this selective retention which serves the adaptation of individuals. In a sense, in this approach, artifacts are the result of adaptations. One famous example provided by Kirch refers to the different types of fishhooks recovered at the different Pacific Islands (Kirch 1980). Using this approach to define tactics and strategies which involve tools and features, it is possible to discuss how large parts of past societies functioned in the past, and Kirch used it – in conjunction with historical linguistics – to explain the process of human colonization of the Pacific Islands (Kirch 2010).
One observation is that many times these approaches assumed that cultural systems were in equilibrium and adaptations were simply seen as including those behaviors “that seemed a reasonable way to maintain the status quo” (Kelly 1995: 47). In the end, it is true that the concept of adaptation is trapped in circular thinking.
Since the 1980s, adaptation is also a core concept of Darwinian or selectionist archaeology. In this approach, tools are seen as the hard parts of the human phenotype, and they are treated as adaptations resulting from the action of natural selection (O’Brien and Holland 1992). The problem is that showing that any given trait was under natural selection is a difficult task at best. Most published applications are restricted to highly specific aspects of past societies, like changes in the shape of projectile points or in the wall thickness of pottery (Neff 1992; O’Brien and Holland 1992). These are attractive and useful examples, but wider applications are still difficult to achieve.
Key Issues/Current Debates
In the twenty-first century, different approaches with a focus on the concept of adaptation are disputing their capacity to deal with the archaeological record. Among these approaches, human behavioral ecology (Bird and O’Connell 2006), selectionism (Dunnell 1980), and cultural macroevolution (Prentiss et al. 2009) are among the best known. Behavioral ecology is “the subset of evolutionary ecology that studies the fitness-related behavioral trade-offs that organisms face in particular environments” (Bird and O’Connell 2006: 144) and includes widely used subfields like costly signaling theory. Basic to these approaches is that natural selection provides the flexibility to adapt to a variety of situations. Extensive ethnoarchaeological and experimental research was done in order to understand the costs and benefits of different tools and strategies. These results are in turn used to discuss diverse aspects of the archaeological record that are not focused in adaptations but result from the process of decision-making allowed by natural selection. Ethnographic data is used not only to develop methodological tools but also to test some of the basic assumptions of behavioral ecology.
Selectionism, on the other hand, tries to explain the archaeological record in terms of the direct action of natural selection (Dunnell 1980; Neff 1992). Adherents to this approach believe that ethnoarchaeology is not useful, since recent societies should be the result of evolutionary forces. For that reason, they should not be adequate to provide good analogs for the past. However, there is a role for experiments, especially those designed to develop engineering principles that can be used to understand the performance of archaeological tools. Many of the most attractive discussions about adaptation produced by selectionists derive from this kind of studies.
Researchers working under the cultural macroevolution brand are concentrating in the study of higher-level cultural entities. This is their basis for the construction of an inclusive macroevolutionary approach to archaeology, which is used to study the evolution of whole cultural systems (Prentiss et al. 2009).
Examples of the identification of archaeological and ethnographic adaptations exist, but there are critiques, importantly that most of the so-called adaptations recorded by ethnographic research cannot be the result of natural selection, because they occurred within one human generation. The main example is the use of snowcats by the Cree that replaced snowshoes in a few years (Boone and Smith 1998). It is indeed difficult to implicate natural selection – a benefit in differential survival – to explain a process that occurred in less than one generation. As a result of all these disagreements, nothing close to an operative application of the concept of adaptation for archaeology emerged. Scheinsohn (2011) maintains that the published examples presented as adaptations are many times in fact either aptations or exaptations, that is, “features coopted for a current utility following an origin for a different function (or for no function at all)” (Gould 2002: 1246). In the end, it appears that it is not reproductive but replicative success that is useful in archaeological studies (Leonard and Jones 1987). Tools can be counted through space and time, and the results can be compared. The assumption is that replicative success derives from the better performance properties of tools, and this is something that we can study in a number of ways. Studies of the resistance of materials, that is, the resistance of ceramics to thermal shock, or the shape of tools, that is, the distribution of cutting edges in lithic tools, can be used to understand the performance potential of different materials. Given the fact that the selective environment is constantly changing, when replication is successful, a number of exaptations are to be expected (Van Pool 2002). For example, most of the morphological transformations of lithic tools are expected to be exaptive. For that reason, it can be suggested that many lithic tools follow an inexorable trend of exaptive transformation. Functional studies, or residue analysis, are adequate ways to study and understand the scope of these variations.
Also, in order to study replicative success per se, engineering studies are useful. These studies are basic components within both the Darwinian or selectionist and behavioral approaches to archaeology. Behavioral archaeology is an approach based on human-artifact interactions that seek to understand cultural change in the long term. In part, this similarity and the idea that “nothing in Darwinian theory per se nor in modern evolutionary biology precludes framing theory and models in behavioral terms” (Schiffer 1996: 96) led Michael Schiffer to propose the existence of important overlaps between both research programs. The answer from the selectionist camp was that differences were still important, including the nomothetic interest which is manifested in the behavioral approach and the corresponding place for historical contingency in the selectionist approach (O’Brien et al. 1998). Beyond these discrepancies, it can be sustained that an understanding of the forces and tensions to which pottery, lithics, or bones are subjected surely helps in the construction of credible adaptive scenarios. These scenarios, in turn, should be able to capture the whole complexity of the cultural systems that produced them.
The study of human bones should be a basic component of any approach that is trying to tackle adaptations in the archaeological record. However, bioanthropology usually appears only through applications of the results of population genetics and molecular biology. This is particularly true in highly speculative scenarios of human colonization of the different regions of the planet. But human bones rarely appear in archaeological discussions of adaptation (but see O’Brien 1987). This is odd, since humans are the carriers of the supposedly adaptive tools and behaviors that we are studying.
One important conclusion is that tools are just means purposefully designed to perform functions. However, intentions can be considered proximate causes at best, and their main role is to generate variation (O’Brien and Holland 1992). Some of the tools recovered in the archaeological record can be seen as exaptations, cases in which the design is not necessarily related with the function but, instead, in the nomenclature of Gould (2002), with its effects. In other words, tools can be used in many unplanned contexts. In one way or the other, it may be true that exaptations can be seen as basic to the understanding of long-term human processes. More specifically, the explicit search for exaptive examples appears today as an archaeologically relevant task, since functions and effects can be understood and temporal changes can be evaluated (Scheinsohn 2011). In a more sophisticated level, exaptations can be invoked even to explain issues like the origins of social inequality or socioeconomic change (Prentiss et al. 2009).
Finally, it is only with the intensive use of bioanthropological information that archaeological discussions of adaptation will find the much desired depth. There is promise in a study that starts with the study of adaptations of the human individual – functional pathologies, stress indicators, stable isotope information, etc. – and then searches for related changes in the frequency of tools or designs. In doing this, we are dealing with conscious or unconscious modifications of behavior (Van Pool 2002: 16) that respond to changes in the social and natural environment. In other words, behaviors, technologies, and phenotypes can be related in complex and difficult to understand loops. Then, an exploration of exaptations, which may be related or not with previous adaptations, appears to be an attractive and promising way to understand the dynamics of past societies.
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