Matt Grove

From Individual Neurons to Social Brains

The manufacture of stone tools is an integral part of the human evolutionary trajectory. However, very little research is directed towards the social and cognitive context of the process of manufacture. This article aims to redress this balance by using insights from contemporary neuroscience. Addressing successively more inclusive levels of analysis, we will argue that the relevant unit of analysis when examining the interface between archaeology and neuroscience is not the individual neuron, nor even necessarily the individual brain, but instead the socio-cognitive context in which brains develop and tools are manufactured and used. This context is inextricably linked to the development of unique ontogenetic scheduling, as evidenced by the fossil record of evolving hominin lineages.

Food and social complexity at Çayönü Tepesi, southeastern Anatolia: Stable isotope evidence of differentiation in diet according to burial practice and sex in the early Neolithic

Highlights ► People from secondary burials (Skull Building) had different diets to those buried beneath houses. ► In the later Cell Plan sub-phase of occupation males and females had different diets. ► Dietary variation resulted from different types and/or amounts of meat and plant protein. ► The isotope results follow sex and burial practice suggesting food reinforced social behaviours.

Space, time, and group size: a model of constraints on primate social foraging

Group size is a fundamental aspect of the adaptation of a social animal to its environment. There have thus been numerous attempts to infer optimal group sizes based on both empirical studies of specific taxa and theoretical models that aim to establish generalities. One such generality is that larger groups experience greater within-group foraging competition because of either direct interference by other group members or the rapid exploitation of resources. The ecological constraints hypothesis proposes that increases in group size will increase intragroup feeding competition, thus forcing individuals to visit more patches and to cover greater areas than they would in smaller groups. This paper provides a simple formal model of this constraint, suggesting that two types of constraint limit group sizes in this scenario. First, a constraint on time available to reach an energetic threshold may limit groups to sizes that allow each individual forager to attain that threshold. Second, the balance of foraging costs to benefits may curtail group size even in the absence of a temporal constraint. Both these constraints can be obviated by the adoption of fission–fusion social systems in which a group divides into subgroups during foraging. This latter finding is discussed in relation to primate social systems with an emphasis on time budget approaches.

Climatic variability, plasticity, and dispersal: A case study from Lake Tana, Ethiopia

The numerous dispersal events that have occurred during the prehistory of hominin lineages are the subject of longstanding and increasingly active debate in evolutionary anthropology. As well as research into the dating and geographic extent of such dispersals, there is an increasing focus on the factors that may have been responsible for dispersal. The growing body of detailed regional palaeoclimatic data is invaluable in demonstrating the often close relationship between changes in prehistoric environments and the movements of hominin populations. The scenarios constructed from such data are often overly simplistic, however, concentrating on the dynamics of cyclical contraction and expansion during severe and ameliorated conditions respectively. This contribution proposes a two-stage hypothesis of hominin dispersal in which populations (1) accumulate high levels of climatic tolerance during highly variable climatic phases, and (2) express such heightened tolerance via dispersal in subsequent low-variability phases. Likely dispersal phases are thus proposed to occur during stable climatic phases that immediately follow phases of high climatic variability. Employing high resolution palaeoclimatic data from Lake Tana, Ethiopia, the hypothesis is examined in relation to the early dispersal of Homo sapiens out of East Africa and into the Levant. A dispersal phase is identified in the Lake Tana record between c. 112,550 and c. 96,975 years ago, a date bracket that accords well with the dating evidence for H. sapiens occupation at the sites of Qafzeh and Skhul. Results are discussed in relation to the complex pattern of H. sapiens dispersal out of East Africa, with particular attention paid to the implications of recent genetic chronologies for the origin of non-African modern humans.

Evolution and dispersal under climatic instability: a simple evolutionary algorithm

It has long been known that temporally unstable environments are likely to promote the evolution of plastic adaptations, whilst it is equally clear that such adaptations are precisely those that characterize successful colonizers. These two established findings, however, are rarely related within a single framework. This article bridges this gap via the development of a very simple evolutionary algorithm that tracks both directional selection and the evolution of plasticity under various synthetic climatic regimes. The output of the model allows for the construction of a dispersal index that provides a measure of population-level dispersal potential under each particular climatic regime. The output thus establishes both the timing and extent of selection for plasticity and the consequences of that plasticity for the timing of probable dispersal events in the context of climatic instability. Results suggest that periods of low climatic instability abruptly following extended periods of higher climatic instability are particularly conducive to dispersal, leading to the formulation of the Accumulated Plasticity Hypothesis. These results, and the hypothesis they support, are discussed in relation to the varied manifestations of plasticity in biological systems and their relevance to human evolution.

Recurrent patterning in the daily foraging routes of hamadryas baboons (Papio hamadryas): Spatial memory in large-scale versus small-scale space

The benefits of spatial memory for foraging animals can be assessed on two distinct spatial scales: small‐scale space (travel within patches) and large‐scale space (travel between patches). While the patches themselves may be distributed at low density, within patches resources are likely densely distributed. We propose, therefore, that spatial memory for recalling the particular locations of previously visited feeding sites will be more advantageous during between‐patch movement, where it may reduce the distances traveled by animals that possess this ability compared to those that must rely on random search. We address this hypothesis by employing descriptive statistics and spectral analyses to characterize the daily foraging routes of a band of wild hamadryas baboons in Filoha, Ethiopia. The baboons slept on two main cliffs—the Filoha cliff and the Wasaro cliff—and daily travel began and ended on a cliff; thus four daily travel routes exist: Filoha–Filoha, Filoha–Wasaro, Wasaro–Wasaro, Wasaro–Filoha. We use newly developed partial sum methods and distribution‐fitting analyses to distinguish periods of area‐restricted search from more extensive movements. The results indicate a single peak in travel activity in the Filoha–Filoha and Wasaro–Filoha routes, three peaks of travel activity in the Filoha–Wasaro routes, and two peaks in the Wasaro–Wasaro routes; and are consistent with on‐the‐ground observations of foraging and ranging behavior of the baboons. In each of the four daily travel routes the “tipping points” identified by the partial sum analyses indicate transitions between travel in small‐ versus large‐scale space. The correspondence between the quantitative analyses and the field observations suggest great utility for using these types of analyses to examine primate travel patterns and especially in distinguishing between movement in small versus large‐scale space. Only the distribution‐fitting analyses are inconsistent with the field observations, which may be due to the scale at which these analyses were conducted. Am. J. Primatol. 76:421–435, 2014.

Counting sheep: sample size and statistical inference in stable isotope analysis and palaeodietary reconstruction

Abstract The analysis of stable isotopes from biological remains has contributed greatly to archaeological knowledge in recent decades, with major contributions to areas such as prehistoric diet and mobility. The increasing importance of isotopic studies within archaeology has been paralleled by an increasing sophistication of laboratory techniques. At present, however, the relationship between sample size and the strength of the conclusions that can be drawn about the underlying population has received insufficient attention. In this paper we undertake to provide a series of statistical analyses that demonstrate the strength of inference in relation to sample size using a large corpus of carbon and nitrogen isotope measurements of bone collagen from a single species at one site (n = 174). We employ a sub-sampling approach to establish sample sizes at which estimated mean values asymptote, and derive confidence intervals accordingly. Our study quantifies the probability that means calculated from samples of various sizes would contain the estimated true value of the population mean with their 95 per cent confidence limits. Using these results, we suggest that large discrepancies should be expected where fewer than eight samples are used to estimate the population mean, but that sampling redundancy occurs with more than forty samples. We would encourage isotope specialists working with other types of material to undertake similar studies in order to better understand the strengths and limitations of stable isotope data.

Did our species evolve in subdivided populations across Africa, and why does it matter?

We challenge the view that our species, Homo sapiens, evolved within a single population and/or region of Africa. The chronology and physical diversity of Pleistocene human fossils suggest that morphologically varied populations pertaining to the H. sapiens clade lived throughout Africa. Similarly, the African archaeological record demonstrates the polycentric origin and persistence of regionally distinct Pleistocene material culture in a variety of paleoecological settings. Genetic studies also indicate that present-day population structure within Africa extends to deep times, paralleling a paleoenvironmental record of shifting and fractured habitable zones. We argue that these fields support an emerging view of a highly structured African prehistory that should be considered in human evolutionary inferences, prompting new interpretations, questions, and interdisciplinary research directions.

Visualisation and permutation methods for archaeological data analysis

Archaeologists routinely analyse bivariate data, whether in raw form or as output from principal components or discriminant function analyses. Often, the aim is to test hypotheses regarding the relationships between two or more groups of data. This paper demonstrates two techniques that are rarely used in archaeology yet, together, refine the presentation and testing of such relationships. Confidence ellipses provide statistically meaningful summaries of location and dispersion, and allow the analyst to judge the feasibility of hypotheses. Permutation tests provide analogues of parametric statistics but do not require the sampling or distributional assumptions that such tests demand; further to this, they have greater statistical power than non-parametric statistics. The value of these two methods in combination is illustrated via a case study of stable isotope ratio data.

Strong conformity requires a greater proportion of asocial learning and achieves lower fitness than a payoff-based equivalent

There is a growing interest in the relative benefits of the different social learning strategies used to transmit information between conspecifics and in the extent to which they require input from asocial learning. Two strategies in particular, conformist and payoff-based social learning, have been subject to considerable theoretical analysis, yet previous models have tended to examine their efficacy in relation to specific parameters or circumstances. This study employs individual-based simulations to derive the optimal proportion of individual learning that coexists with conformist and payoff-based strategies in populations experiencing wide-ranging variation in levels of environmental change, reproductive turnover, learning error and individual learning costs. Results demonstrate that conformity coexists with a greater proportion of asocial learning under all parameter combinations, and that payoff-based social learning is more adaptive in 97.43% of such combinations. These results are discussed in relation to the conjecture that the most successful social learning strategy will be the one that can persist with the lowest frequency of asocial learning, and the possibility that punishment of non-conformists may be required for conformity to confer adaptive benefits over payoff-based strategies in temporally heterogeneous environments.