Convergent Evolution in Stone-Tool Technology by Convergent Evolution in Stone-Tool Technology

Author:Convergent Evolution in Stone-Tool Technology [Retail]
Language: eng
Format: epub
Tags: archaeology; paleontology; paleoanthropology; convergence; evolutionary convergence; evolution of behavior; lithic; evolution of technology; Paleolithic; Holocene; social learning; hominin
Publisher: MIT Press
Published: 2018-05-18T00:00:00+00:00

How Do We Solve the “IUP Problem”?

Fortunately, a range of conceptual and analytical models exist for distinguishing among the effects of population movement, diffusion of cultural knowledge, and independent invention, although it is not our intention to review them here. Our concern here is more basic, namely the selection of appropriate models and variables on which to base the analysis.

Transmission, Parsimony, and Other Models

As some participants in the Konrad Lorenz Institute workshop noted, phylogenetic analyses based on phenotypic traits can be unreliable compared to the gold standard of studies based on genetics (e.g., Collard and Wood 2000). For one thing, phenotypic traits are not what is actually inherited, and many phenotypic characters map imperfectly onto genetic units. To cite a much-discussed example, the phenotypes of chimpanzees are rather similar, but the species’ genome is relatively diverse. The opposite can be observed among humans, who show high morphological diversity but low genetic diversity. These differences suggest that selection and especially plasticity play large roles in structuring the phenotypic diversity observed among current and past populations.

Maximum parsimony, one commonly used method in phylogenetic analysis, implies that homologies are more common than convergences. It builds trees with the least complex branching, and the most parsimonious trees minimize the amount of convergence. Although it has proven to be misleading, parsimony may work in situations where rates of change are known. And that could be a major concern when dealing with material culture. Phylogenetic analyses based on morphological traits of extant species are often combined with genetic analysis, where assumptions about coalescence times are based on mutation rates. In such cases, the phenotype is used as proxy for detecting selection, whereas the model of transmission is based on genetic transmission. With the fossil record, traits are supposed to be—at least for the most part—transmitted along with the coded part of the genome, and traits observed on bones are used as a proxy to infer a phylogeny in the absence of genetic data. When dealing with material culture, we have no analogue for the genetic models. It is unlikely that we will ever know exactly what people learned in the past and from whom they learned it. So if we are to ask questions about phylogenetic connections and convergence among archaeological assemblages, we have the choice of either (a) designing an overly simplistic model specific to cultural transmission or (b) using parsimony and assuming that traits were typically transmitted gradually and vertically. Here, we use artifacts as analogues for phenotypic information.

It sounds like a difficult dilemma, but just because the tool is imperfect does not mean we should not use it, especially when it is the only device available. The more important point is that phylogenetic analyses can be used to build hypotheses and compare those with what we know about the dates and locations of assemblages. While we do not have genetics to fall back on, we do have some independent control over relationships among the makers of the various assemblages, namely the dimensions of time and space.

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