Inference from large sets of radiocarbon dates: Software and methods

ABSTRACTThe last decade has seen the development of a range of new statistical and computational techniques for analysing large collections of radiocarbon (14C) dates, often but not exclusively to make inferences about human population change in the past. Here we introduce rcarbon, an open-source software package for the R statistical computing language which implements many of these techniques and looks to foster transparent future study of their strengths and weaknesses. In this paper, we review the key assumptions, limitations and potentials behind statistical analyses of summed probability distribution of 14C dates, including Monte-Carlo simulation-based tests, permutation tests, and spatial analyses. Supplementary material provides a fully reproducible analysis with further details not covered in the main paper.ER

The cultural evolution of adaptive-trait diversity when resources are uncertain and finite

In this paper, we seek to build on existing mathematical studies of cultural change by exploring how the diversity of adaptive cultural traits evolves by innovation and cultural transmission when the payoff from adopting traits is both uncertain and frequency dependent. The model is particularly aimed at understanding the evolution of subsistence trait diversity, since the payoff from exploiting particular resources is often variable and subject to diminishing returns as a result of overexploitation. We find that traits that exploit the same shared resource evolve most quickly when intermediate rates of cultural transmission promote fluctuation in trait diversity. Higher rates of cultural transmission, which promote predominantly low diversity, and lower rates, which promote predominantly high diversity, both retard the adoption of traits offering higher payoff. We also find that the distribution of traits that exploit independent resources can evolve towards the theoretical Ideal Free Distribution so long as the rate of cultural transmission is low. Increasing the rate of cultural transmission reduces trait diversity, so that a more limited number of "niches" are occupied at any given time

Risk factors for the occurrence of sexual misconduct during archaeological and anthropological fieldwork

AbstractFieldwork is crucial to advancing knowledge in archaeology and anthropology, but previous works suggests that between 64 and 68 percent of respondents experience sexual misconduct during fieldwork. Going forward, fieldwork must be made safe and inclusive. To achieve this, we must understand why sexual misconduct takes place during fieldwork. We surveyed an international sample of archaeologists and anthropologists (n=300) about their most recent fieldwork experience. We examine evidence for risk factors predicting sexual misconduct in fieldsites, and our findings suggest that length of fieldwork, presence and communication of policies and protocols, and the gender and sexuality of the individual are all significant. In particular, we find evidence for increased risk to nonmale and nonheterosexual individuals. We also gathered qualitative evidence from our respondents, who reported that in some cases they were discouraged from reporting and faced retaliation, they were dissatisfied with the handling of complaints, and fieldsite policies and protocols were not consistently or effectively implemented. Fieldwork can be a high‐risk environment for marginalized individuals to experience sexual misconduct, and when clear policies and procedures are lacking, it can also be a low‐risk environment for perpetrators in terms of consequences. To make fieldwork a safe environment for all, policies and protocols that mitigate the risk of sexual misconduct must be consistently implemented and properly communicated.</jats:p

Modifiable reporting unit problems and time series of long-term human activity.

This paper responds to a resurgence of interest in constructing long-term time proxies of human activity, especially but not limited to models of population change over the Pleistocene and/or Holocene. While very much agreeing with the need for this increased attention, we emphasize three important issues that can all be thought of as modifiable reporting unit problems: the impact of (i) archaeological periodization, (ii) uneven event durations and (iii) geographical nucleation-dispersal phenomena. Drawing inspiration from real-world examples from prehistoric Britain, Greece and Japan, we explore their consequences and possible mitigation via a reproducible set of tactical simulations. This article is part of the theme issue 'Cross-disciplinary approaches to prehistoric demography'.ERC Stg Grant (ENCOUNTER Project - 801953

Spatial and Temporal Models of Jomon Settlement

The Jomon culture is a tradition of complex hunter-gatherers which rose in the Japanese archipelago at the end of the Pleistocene (ca. 13,000 cal BP) and lasted until the 3rd millennium cal BP. Recent studies increasingly suggest how this long cultural persistence was characterised by repeated episodes of change in settlement pattern, primarily manifested as cyclical transitions between nucleated and dispersed distributions. Although it has been suggested that these events correlate with population dynamics, shifts in subsistence strategies, and environmental change, to date there have been very few attempts to provide a quantitative analysis of spatio-temporal change in Jomon settlement and its possible causes. This thesis is an attempt to fill that lacuna by adopting a twin-track approach to the problem. First, two case studies from central Japan have been examined using a novel set of methods, which have been specifically designed to handle the intrinsic chronological uncertainty which characterises most prehistoric data. This facilitated the application of a probabilistic framework for quantitatively assessing the available information, making it possible to identify alternating phases of nucleated and dispersed pattern during a chronological interval between 7000 and 3300 cal BP. Second, computer simulation (by means of an agent-based model) has been used to carry out a formal inquiry into the possible underlying processes that might have triggered the observed changes in the settlement pattern. The aim of this simulation exercise was two-fold. First, it has been used as a theory-building tool, combining several models from behavioural ecology and cultural transmission theory in order to provide explicit expectations in relation to the presence and absence of environmental disturbances. Second, the outcome of the simulation has been used as a template for linking the observed patterns to possible underlying socio-ecological processes suggested by the agent-based model. This endeavour has shown how some of the largest changes in the empirically observed settlement patterns can be simulated as emerging from the internal dynamics of the system rather than necessarily being induced by external changes in the environment

Revealing patterns of cultural transmission from frequency data: equilibrium and non-equilibrium assumptions

A long tradition of cultural evolutionary studies has developed a rich repertoire of mathematical models of social learning. Early studies have laid the foundation of more recent endeavours to infer patterns of cultural transmission from observed frequencies of a variety of cultural data, from decorative motifs on potsherds to baby names and musical preferences. While this wide range of applications provides an opportunity for the development of generalisable analytical workflows, archaeological data present new questions and challenges that require further methodological and theoretical discussion. Here we examine the decorative motifs of Neolithic pottery from an archaeological assemblage in Western Germany, and argue that the widely used (and relatively undiscussed) assumption that observed frequencies are the result of a system in equilibrium conditions is unwarranted, and can lead to incorrect conclusions. We analyse our data with a simulation-based inferential framework that can overcome some of the intrinsic limitations in archaeological data, as well as handle both equilibrium conditions and instances where the mode of cultural transmission is time-variant. Results suggest that none of the models examined can produce the observed pattern under equilibrium conditions, and suggest. instead temporal shifts in the patterns of cultural transmission.The authors acknowledge the use of the UCL Legion High Performance Computing Facility (Legion@UCL), and associated support services, in the completion of this work. This work was financially supported by the McDonald Institute for Archaeological Research and by an European Research Council Advanced Grant, project #249390(EUROEVOL, Cultural Evolution of Neolithic Europe)

How Cultural Transmission Through Objects Impacts Inferences About Cultural Evolution

The cross-fertilisation between biological and cultural evolution has led to an extensive borrowing of key concepts, theories, and statistical methods for studying temporal variation in the frequency of cultural variants. Archaeologists have been among the front-runners of those engaging with this endeavour, and the last 2 decades have seen a number of case studies where modes of social learning were inferred from the changing frequencies of artefacts. Here, we employ a simulation model to review and examine under-discussed assumptions shared by many of these applications on the nature of what constitutes the 'population' under study. We specifically ask (1) whether cultural transmission via 'objects' (i.e. public manifestations of cultural traits) generates distinct patterns from those expected from direct transmission between individuals and (2) whether basing inference on the frequency of objects rather than on the frequency of mental representations underlying the production of those objects may lead to biased interpretations. Our results show that the rate at which ideational cultural traits are embedded in objects, and shared as such, has a measurable impact on how we infer cultural transmission processes when analysing frequency-based archaeological data. At the same time, when cultural transmission is entirely mediated by the material representation of ideas, we argue that copying error should be interpreted as a two-step process which may occur in either one or both of embedding information in objects and retrieving it from them

Culture, space, and metapopulation: a simulation-based study for evaluating signals of blending and branching

This paper explores the robustness of phylogenetic methods for detecting variations in branching and blending signals in the archaeological record. Both processes can generate a spatial structure whereby cultural similarity between different sites decays with increasing spatial distance. By generating a series of artificial records through the controlled and parameterised environment of an agent-based simulation, we: a) illustrate the weakness and the strength of different analytical techniques (empirical distogram, Mantel test, Retention Index, and d-score); b) determine whether they are capable of assessing how spatial isolation determines cultural diversity; and c) establish whether they can detect variations in the nature of horizontal transmission over time. Results suggest that variables other than the spatial range of interaction (e.g. the frequency of fission events, population dynamics, and rates of cultural innovation) have different effects on the output of some phylogenetic analyses

A House with a View? Multi-model inference, visibility fields, and point process analysis of a Bronze Age settlement on Leskernick Hill (Cornwall, UK)

This paper combines point-process modelling, visibility analysis and an information criteria approach to infer the reasons behind the Bronze Age settlement pattern of Leskernick Hill in Cornwall, UK. We formalise three alternative hypotheses as point process models characterised by different combinations of covariates. In addition to using traditional topographic variables, we use a form of affordance viewsheds, which we refer to as visibility fields, to investigate the visual properties of different parts of the landscape, both cultural and natural. We compare these three models by means of information criteria, and generate a fourth hybrid model by recombining variables drawn from each. The results reveal that a mixture of covariates drawn from the three hypotheses combined with a spatial interaction model provides the best overall model for the settlement pattern. We show that the settlement on Leskernick Hill was most likely the result of two separate decision-making processes, one to optimise the visibility of ritual monuments and important natural landmarks, and the other to optimise the visibility of nearby tin-extraction areas. We conclude that by using an information criterion approach it is possible to easily compare the models and identify which among these is the most satisfying in the present state of our knowledge

Spatio-temporal approaches to archaeological radiocarbon dates

Summed probability distributions of radiocarbon dates are an increasingly popular means by which to reconstruct prehistoric population dynamics, enabling more thorough cross-regional comparison and more robust hypothesis testing, for example with regard to the impact of climate change on past human demography. Here we review another use of such summed distributions – to make spatially explicit inferences about geographic variation in prehistoric populations. We argue that most of the methods proposed so far have been strongly biased by spatially varying sampling intensity, and we therefore propose a spatial permutation test that is robust to such forms of bias and able to detect both positive and negative local deviations from pan-regional rates of change in radiocarbon date density. We test our method both on some simple, simulated population trajectories and also on a large real-world dataset, and show that we can draw useful conclusions about spatio-temporal variation in population across Neolithic Europe