On some statistical and cerebral aspects of the limits of working memory capacity in anthropoid primates, with particular reference to Pan and Homo, and their significance for human evolution.

Some comparative ontogenetic data imply that effective working-memory capacity develops in ways that are independent of brain size in humans. These are interpreted better from neuroscientific considerations about the continuing development of neuronal architecture in adolescents and young adults, than from one about gross brain mass which already is reached in childhood. By contrast, working-memory capacity in Pan never develops beyond that of three- or four-year-old children. The phylogenetic divergence begs the question of whether it is any longer plausible to infer from the fossil record, that over the past two million years, an ostensibly gradual increase in endocranial volumes, assigned to the genus Homo, can be correlated in a scientifically-meaningful manner with the gradual evolution of our effective executive working memory. It is argued that whereas Pan's effective working-memory capacity is relatively similar to that of its storage working-memory, our working memory is relatively larger with deeper executive control.

On the working memory of humans and great apes: Strikingly similar or remarkably different?

In this article we review publications relevant to addressing widely reported claims in both the academic and popular press that chimpanzees working memory (WM) is comparable to, if not exceeding, that of humans. WM is a complex multidimensional construct with strong parallels in humans to prefrontal cortex and cognitive development. These parallels occur in chimpanzees, but to a lesser degree. We review empirical evidence and conclude that the size of WM in chimpanzees is 2 ± 1 versus Miller's famous 7 ± 2 in humans. Comparable differences occur in experiments on chimpanzees relating to strategic and attentional WM subsystems. Regardless of the domain, chimpanzee WM performance is comparable to that of humans around the age of 4 or 5. Next, we review evidence showing parallels among the evolution of WM capacity in hominins ancestral to Homo sapiens, the phylogenetic evolution of hominins leading to Homo sapiens, and evolution in the complexity of stone tool technology over this time period.

Behavioural mimicry as an indicator of affiliation.

Previous research has shown that behavioural mimicry fosters affiliation, and can be used to infer whether people belong to the same social unit. However, we still know very little about the generalizability of these findings and the individual factors involved. The present study intends to disentangle two important variables and assess their importance for affiliation: the matching in time of the behaviours versus their matching in form. In order to address this issue, we presented participants with short videos in which two actors displayed a set of small movements (e.g. crossing their legs, folding their arms, tapping their fingers) arranged to be either contingent in time or in form. A dark filter was used to eliminate ostensive group marks, such us phenotype or clothing. Participants attributed the highest degree of affiliation to the actors when their subsequent movements matched in form, but were delayed by 4-5 seconds, and the lowest degree when the timing of their movements matched, but they differed in form. To assess the generalizability of our findings, we took our study outside the usual Western context and tested a matching sample of participants from a traditional small-scale society in Kenya. In all, our results suggest that movements are used to judge the degree of affiliation between two individuals in both large- and small-scale societies. While moving in different ways at the same time seems to increase the perceived distance between two individuals, movements which match in form seem to invoke closeness.

The rich detail of cultural symbol systems.

The goal of forming a science of intentional behavior requires a more richly detailed account of symbolic systems than is assumed by the authors. Cultural systems are not simply the equivalent in the ideational domain of culture of the purported Baldwin Effect in the genetic domain.

The substance of cultural evolution: culturally framed systems of social organization.

Models of cultural evolution need to address not only the organizational aspects of human societies, but also the complexity and structure of cultural idea systems that frame their systems of organization. These cultural idea systems determine a framework within which behaviors take place and provide mutually understood meanings for behavior from the perspective of both agent and recipient that are critical for the coherence of human systems of social organization.

Emergent properties in small-scale societies.

A multi-agent simulation is used to explore the relationship between the micro and the macro levels in small-scale societies. The simulation demonstrates, using an African hunter-gatherer group (the !Kung san) as a case study, the way in which population stability may arise from culturally framed, micro-level decision making by women about spacing of births. According to the simulation, population stability as an emergent property has different implications, depending on resource density. Data on Australian hunter-gatherer groups are presented that support the implications of the simulation. !Kung san micro-level cultural rules on incestuous marriages are shown to have macro-level consequences in the form of marriages between residential camps. Between-camp marriages have significant implications for access to resources and thereby for population dynamics of the group as a whole.

A multitrajectory, competition model of emergent complexity in human social organization.

The repeated pattern of emergent human organization at a societal level going from small-scale, egalitarian decentralized societies to complex, stratified, and centralized societies is well-documented in the archaeological record of past societies. In this paper, I outline a multitrajectory model that relates to the broad features of this sequence of societal change. Competition is shown to play a critical role in the way interaction--among decision making, demographic parameters, and social units that organize resource ownership and procurement--either promotes or inhibits change in social organization. Multiagent simulation is discussed as a way to link culturally embedded decision making to emergent properties in the multitrajectory model.