Evolutionary Biological Methods and Cultural Data
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CHAPTER 13 Evolutionary Biological Methods and Cultural Data MARK COLLARD, STEPHEN SHENNAN, BRIGGS BUCHANAN, AND R. ALEXANDER BENTLEY As BENTLEY ET AL. note in chapter 8 of this volume, reproductive success or primarily through phenotypic Darwinian approaches to archaeology are rapidly plasticity. The former simply involves some individu gaining popularity, fueled in part by the recognition als outreproducing others; the latter is the ability ofor that cultural evolution can be fruitfully studied by ganisms to produce different phenotypes in response adapting the analytical tools that evolutionary biolo to different environmental conditions (Pigilucci 1996). gists and paleobiologists use to study biological evolu The schools of thought also differ over the role played tion. The goal of this chapter is to illustrate how two by population-level phenomena in cultural evolution. of these methods, population genetics modeling and These differences impact the way proponents of the cladistic techniques of phylogenetic reconstruction, three schools of thought envisage the relationship can be used to explain temporal and geographic varia between cultural evolution and genetic evolution, and tion in cultural phenomena as a result oftransmission, also affect their attitude toward adaptively neutral and innovation, and selection. We will begin by discussing maladaptive cultural behaviors. the conceptual foundations ofthis novel approach. We The central tenet ofevolutionary archaeology is that will then outline some of the ways in which models artifacts are as much a part of the human phenotype rooted in population genetics theory have been used as are bones, muscle, and skin (Dunnell 1989; Leonard to investigate cultural evolution. Lastly, we will discuss 2001; Lyman and O'Brien 1998; O'Brien and Holland some cultural evolutionary applications of the cladis 1995). The corollary of this is that evolutionary ar tic method of phylogenetic reconstruction. chaeologists seek to describe the archaeological record using classes amenable to evolutionary explanation CONCEPTUAL FOUNDATIONS (Cochrane 2001; Dunnell 1978, 1995; Tschauner 1994) Proponents of three schools of thought have applied and then account for the class distributions in terms of population genetics modeling and cladistic techniques what they consider to be the primary mechanisms of to cultural data. The first is evolutionary archaeology, evolution, namely natural selection and drift (Abbott which is also occasionally referred to as selectionist et aI. 1996; Braun 1987; Dunnell and Feathers 1991; archaeology (Abbott et aI. 1996; Dunnell 1980, 1989; Leonard 2001; Lyman and O'Brien 1998; O'Brien and Leonard and Jones 1987; Leonard 2001; Lipo et aI. Lyman 2000; Ramenofsky 1995). 1997; Lyman and O'Brien 1998; Neff 1992; O'Brien Explaining what evolutionary archaeologists mean and Holland 1995; O'Brien and Lyman 2000, 2002, by the terms "natural selection" and "drift" is not easy 2003a; Ramenofsky 1995). The second is gene culture because the definitions they have put forward differ in coevolution theory or dual inheritance theory (Ames subtle but potentially important ways. This point can 1996; Bettinger 1991; Boyd and Richerson 1985, 1993; be illustrated by comparing the definitions of natural Cavalli-Sforza and Feldman 1981; Durham 1979, 1982, selection and drift provided by Wilhelmsen (200 1) and 1990, 1991, 1992; Pulliam and Dunford 1980; Richer O'Brien and Lyman (2000), which seem to represent the son and Boyd 1992; Runciman 2002; Shennan 1991, extremes of a range ofviews. According to Wilhelmsen 2000,2002). The third is known as human behavioral (2001), natural selection is "the differential reproduc ecology (Borgerhoff Mulder 1991; Cronk 1991; Shen tion of organisms which, at the scale of population, nan 2002; Smith 2000; Smith and Winterhalder 1992; results in a directional change in trait frequencies over Smith et aI. 2001; Winterhalder and Smith 2000). time that correlates to external environmental condi These schools of thought differ over whether cultural tions" (p. 99), and drift is the differential reproduction evolution is effected primarily through differential of organisms as a result of "sampling error and the 203 stochastic patterns oftransmission" (p. 100). According where the forms are artifacts and the increase is brought to O'Brien and Lyman (2000), selection is the "process about through cultural transmission. In other words, it by which certain forms in a population that are better is possible that some evolutionary archaeologists take adapted to a particular environment increase in pro seriously the possibility that change in the archaeologi portion to less well-adapted forms" (p. 404), and drift cal record may be the result of phenotypic plasticity as is "random changes in trait frequency in a population well as differential reproductive success rather than just resulting from the vagaries of transmission" (p. 399). the result ofthe latter. In keeping with this, O'Brien and One of the differences between the definitions is that Lyman (2000) have noted that explanations of artifact Wilhelmsen's (200l) focuses on "organisms" whereas class distributions and human biological reproduction O'Brien and Lyman's (2000) definition of selection may be generated at different analytical scales. Likewise, and, by extension, their definition of drift, focuses on Leonard and Jones (1987; Leonard 200l) have drawn a "forms." The other difference concerns the mechanisms distinction between the replicative success of cultural of change involved in selection and drift. Wilhelmsen's traits and the reproductive success of individuals, and (2001) definition ofselection explicitly links it with dif argued that the former should not be assumed to be ferential reproduction. That is, his definition suggests reducible to the latter. that in the case ofselection, changes in trait frequencies However, having reviewed a good deal of the work over time are the result of some individuals producing that has been produced by evolutionary archaeologists more offspring than others. In contrast, O'Brien and over the past thirty years, we are ofthe opinion that the Lyman's (2000) definition of selection does not men differences between the definitions offered by Wilhelm tion differential reproduction. Indeed, no mechanism sen (2001) and O'Brien and Lyman (2000) are notin fact of change is specified. Selection is suggested to involve significant. O'Brien and Lyman (2000) and most other better adapted forms increasing in frequency at the evolutionary archaeologists normally dismiss the possi expense of less well-adapted forms, but the manner in bility ofchange occurring as a consequence ofindividu which this occurs is not specified. The situation is simi als copying behaviors and then modifying them in light lar with drift; Wilhelmsen's (200l) definition explic ofexperience before passing them on. They also usually itly links drift with differential reproduction, whereas treat transmission as if it occurs solely from parents to O'Brien and Lyman's (2000) definition does not men offspring, ignoring the various other forms of cultural tion differential reproduction. Rather, for O'Brien and transmission, which, as noted earlier, can in principle Lyman (2000) drift is the consequence of the "vagaries lead to the oblique and horizontal movement ofcultural oftransmission." traits among individuals and populations in the absence These differences are potentially important because, of gene flow (e.g., Abbott et al. 1996; Leonard 2001; together, they bear on the way in which evolutionary O'Brien and Lyman 2000; Ramenofsky 1995). Thus in archaeologists conceptualize the relationship between practice, evolutionary archaeologists treat cultural evo genetic evolution and cultural evolution. By linking lution as if it is effected primarily through differential selection directly with differential reproduction of or reproductive success, and therefore do not allow for the ganisms, Wilhelmsen's (2001) definitions of natural se possibility that genes and culture may have different lection and drift imply that culture evolves in exactly evolutionary dynamics. Significantly, our characteriza the same manner as genes, and that cultural evolution tion ofevolutionary archaeology seems to be in line with is therefore reducible to genetic evolution. In contrast, that of O'Brien and Lyman (2002:35), who note that O'Brien and Lyman's (2000) focus on forms rather than whereas "some behavioral ecologists argue that much of organisms and their decision to leave the mechanism of the change we see archaeologically is attributable to phe change unspecified opens up the possibility that O'Brien notypic plasticity ... most evolutionary archaeologists and Lyman (2000) recognize that genetic evolution and would argue that much ofit is attributable to selection." cultural evolution involve different mechanisms and In contrast to evolutionary archaeology, dual inher therefore potentially have different dynamics. Thus it itance theory treats cultural evolution as ifit is primar is possible that O'Brien and Lyman (2000) and some ily effected through phenotypic plasticity rather than other evolutionary archaeologists consider selection to differential reproductive success. In dual inheritance involve not onlyincrease in relative frequency ofadapted theory, genes and culture are viewed as two distinct forms where the forms are organisms and the increase but interacting systems of information transmission