Research in anthropology has shown that kin terminologies have a complex combinatorial structure and vary systematically across cultures. This article argues that universals and variation in kin terminology result from the interaction of (1) an innate conceptual structure of kinship, homologous with conceptual structure in other domains, and (2) principles of optimal, “grammatical” communication active in language in general. Kin terms from two languages, English and Seneca, show how terminologies that look very different on the surface may result from variation in the rankings of a universal set of constraints. Constraints on kin terms form a system: some are concerned with absolute features of kin (sex), others with the position (distance and direction) of kin in “kinship space,” others with groups and group boundaries (matrilines, patrilines, generations, etc.). Also, kin terms sometimes extend indefinitely via recursion, and recursion in kin terminology has parallels with recursion in other areas of language. Thus the study of kinship sheds light on two areas of cognition, and their phylogeny. The conceptual structure of kinship seems to borrow its organization from the conceptual structure of space, while being specialized for representing genealogy. And the grammar of kinship looks like the product of an evolved grammar faculty, opportunistically active across traditional domains of semantics, syntax, and phonology. Grammar is best understood as an offshoot of a uniquely human capacity for playing coordination games.

Recent application of theories of embodied or grounded cognition to the recognition and interpretation of facial expression of emotion has led to an explosion of research in psychology and the neurosciences. However, despite the accelerating number of reported findings, it remains unclear how the many component processes of emotion and their neural mechanisms actually support embodied simulation. Equally unclear is what triggers the use of embodied simulation versus perceptual or conceptual strategies in determining meaning. The present article integrates behavioral research from social psychology with recent research in neurosciences in order to provide coherence to the extant and future research on this topic. The roles of several of the brain's reward systems, and the amygdala, somatosensory cortices, and motor centers are examined. These are then linked to behavioral and brain research on facial mimicry and eye gaze. Articulation of the mediators and moderators of facial mimicry and gaze are particularly useful in guiding interpretation of relevant findings from neurosciences. Finally, a model of the processing of the smile, the most complex of the facial expressions, is presented as a means to illustrate how to advance the application of theories of embodied cognition in the study of facial expression of emotion.

Behavioral scientists routinely publish broad claims about human psychology and behavior in the world's top journals based on samples drawn entirely from Western, Educated, Industrialized, Rich, and Democratic (WEIRD) societies. Researchers – often implicitly – assume that either there is little variation across human populations, or that these “standard subjects” are as representative of the species as any other population. Are these assumptions justified? Here, our review of the comparative database from across the behavioral sciences suggests both that there is substantial variability in experimental results across populations and that WEIRD subjects are particularly unusual compared with the rest of the species – frequent outliers. The domains reviewed include visual perception, fairness, cooperation, spatial reasoning, categorization and inferential induction, moral reasoning, reasoning styles, self-concepts and related motivations, and the heritability of IQ. The findings suggest that members of WEIRD societies, including young children, are among the least representative populations one could find for generalizing about humans. Many of these findings involve domains that are associated with fundamental aspects of psychology, motivation, and behavior – hence, there are no obvious a priori grounds for claiming that a particular behavioral phenomenon is universal based on sampling from a single subpopulation. Overall, these empirical patterns suggests that we need to be less cavalier in addressing questions of human nature on the basis of data drawn from this particularly thin, and rather unusual, slice of humanity. We close by proposing ways to structurally re-organize the behavioral sciences to best tackle these challenges.

What motivates grandparents to their altruism? We review answers from evolutionary theory, sociology, and economics. Sometimes in direct conflict with each other, these accounts of grandparental investment exist side-by-side, with little or no theoretical integration. They all account for some of the data, and none account for all of it. We call for a more comprehensive theoretical framework of grandparental investment that addresses its proximate and ultimate causes, and its variability due to lineage, values, norms, institutions (e.g., inheritance laws), and social welfare regimes. This framework needs to take into account that the demographic shift to low fecundity and mortality in economically developed countries has profoundly altered basic parameters of grandparental investment. We then turn to the possible impact of grandparental acts of altruism, and examine whether benefits of grandparental care in industrialized societies may manifest in terms of less tangible dimensions, such as the grandchildren's cognitive and verbal ability, mental health, and well-being. Although grandparents in industrialized societies continue to invest substantial amounts of time and money in their grandchildren, we find a paucity of studies investigating the influence that this investment has on grandchildren in low-risk family contexts. Under circumstances of duress – for example, teenage pregnancy or maternal depression – there is converging evidence that grandparents can provide support that helps to safeguard their children and grandchildren against adverse risks. We conclude by discussing the role that grandparents could play in what has been referred to as Europe's demographic suicide.

An emerging class of theories concerning the functional structure of the brain takes the reuse of neural circuitry for various cognitive purposes to be a central organizational principle. According to these theories, it is quite common for neural circuits established for one purpose to be exapted (exploited, recycled, redeployed) during evolution or normal development, and be put to different uses, often without losing their original functions. Neural reuse theories thus differ from the usual understanding of the role of neural plasticity (which is, after all, a kind of reuse) in brain organization along the following lines: According to neural reuse, circuits can continue to acquire new uses after an initial or original function is established; the acquisition of new uses need not involve unusual circumstances such as injury or loss of established function; and the acquisition of a new use need not involve (much) local change to circuit structure (e.g., it might involve only the establishment of functional connections to new neural partners). Thus, neural reuse theories offer a distinct perspective on several topics of general interest, such as: the evolution and development of the brain, including (for instance) the evolutionary-developmental pathway supporting primate tool use and human language; the degree of modularity in brain organization; the degree of localization of cognitive function; and the cortical parcellation problem and the prospects (and proper methods to employ) for function to structure mapping. The idea also has some practical implications in the areas of rehabilitative medicine and machine interface design.

The effects of grandparental investment in relatives are apparent in human groups, suggesting that a postreproductive period in humans is selective. Although investment of relatives in kin produces obvious benefits for kin groups, selection for a postreproductive period in humans is not supported by evidence from chimpanzees. Instead, grandparental investment is likely a recent phenomenon of longevity, rather than an evolved feature.

We welcome the critical appraisal of the database used by the behavioral sciences, but we suggest that the authors' differentiation between variable and universal features is ill conceived and that their categorization of non-WEIRD populations is misleading. We propose a different approach to comparative research, which takes population variability seriously and recognizes the methodological difficulties it engenders.

According to the SIMS model, mimicry and simulation contribute to perceivers' understanding of smiles. We argue that similar mechanisms are involved in comprehending the hand gestures that people produce when speaking. Viewing gestures may elicit overt mimicry, or may evoke corresponding simulations in the minds of addressees. These real or simulated actions contribute to addressees' comprehension of speakers' gestures.

Simple specialization cannot account for brain functioning. Yet, we believe Anderson's reuse can be better explained by re-function. We suggest that functional demands shape brain changes and are the driving force behind reuse. For example, we suggest that the prefrontal cortex (PFC) is built as an infrastructure for multi-functions rather than as a module for reuse.

Jones introduces an intricate machinery of kin classification that overcomes limitations of previous accounts. I question whether such a machinery is plausible. Because individuals never need to learn the entire spectrum of kin terminology, they could rely on data-driven learning. The complexity of Jones's machinery for kin classification casts doubt on the existence of innate structures that cover the complete linguistic domain.

Niedenthal et al. present a model for embodied emotion simulation and expression understanding that spans multiple brain systems. This commentary addresses the potential role of time in this model, and its implications for understanding social dysfunction.

Recent work on the evolution of utility has brought the blunt instrument of kin selection closer to the cluttered scalpel kit of social science. The concept of diminishing marginal utility can help streamline the latter. Reconciling ultimate causes with proximate inclinations, however, will be easier for the case of assistance from grandparents than assistance to them.

While we agree that the cultural imbalance in the recruitment of participants in psychology experiments is highly detrimental, we emphasize the need to complement this criticism with a warning about the “weirdness” of some cross-cultural studies showing seemingly deep cultural differences. We take the example of economic games and suggest that the variety of results observed in these games may not be due to deep psychological differences per se, but rather due to different interpretations of the situation.

Mere physical experiences of warmth, distance, hardness, and roughness are found to activate the more abstract psychological concepts that are analogically related to them, such as interpersonal warmth and emotional distance, thereby influencing social judgments and interpersonal behavior without the individual's awareness. These findings further support the principle of neural reuse in the development and operation of higher mental processes.

In this commentary, I focus on Jones' suggestion of a close connection between the domain of space and that of kinship. I expand on that suggestion by introducing the concept of frame of reference and show how it can possibly participate to the generation of kinship systems.

In order to evaluate the impact of contemporary grandparenting, the view should not be restricted to developmental achievement effects in grandchildren. Both child happiness and grandparent happiness are high-ranking goals with implications for public policy. The beneficial impact of grandparenting for risk families appears unequivocal, and modern life still encounters all kinds of unpredictable risks. Contemporary grandparental care is no evolutionary mismatch.

The SIMS model offers an embodied perspective to cognition and behaviour that can be applied to organizational studies. This model enriches behavioural and brain research conducted by social scientists on emotional work (also known as emotional labour) by including the key role played by body-related aspects in interpersonal exchanges. Nevertheless, one could also study a more vocal aspect to smiling as illustrated by the development of “smile down the phone” strategies in organizations. We propose to gather face-to-face and voice-to-voice interactions in an embodied perspective taking into account Lakoff and Johnson's (1980) theory of conceptual metaphors.

Henrich et al.'s critical review demonstrating that psychology research is over-reliant on WEIRD samples is an important contribution to the field. Their stronger claim that “WEIRD subjects are particularly unusual” is less convincing, however. We argue that WEIRD people's apparent distinct weirdness is a methodological side-effect of psychology's over-reliance on WEIRD populations for developing its methods and theoretical constructs.

To establish Optimality Theory as a framework in anthropology, or as a general model of higher human cognition, researchers have to demonstrate OT is convincing in a number of ways. This commentary summarizes some of them – based on experience obtained in contemporary linguistic OT – including factorial typologies, exact formulation of candidate sets and constraints, and computational plausibility.

Neural reuse theories suggest that, in the course of evolution, a brain structure may acquire or lose a number of cognitive uses while maintaining its cognitive workings (or low-level operations) fixed. This, in turn, suggests that homologous structures may have very different cognitive uses, while sharing the same workings. And this, essentially, is homology thinking applied to brain function.