The dance metaphor for the communication between two organisms may be an appealing image because it appears to capture the intricate synchronization of their interaction; however, it is neither parsimonious nor easily tested. Instead, a multichannel information-processing model, even one that can process only serial events, provides all of the flexibility required to account for the complex temporal coordinated action observed.

Although antiadaptationist authors encourage us to consider alternatives to adaptationist positions, the alternatives offered do not necessarily relieve us of the burdens of adaptationist explanations. Even if something is an exaptation, it may be derived from an adaptation. If it is a byproduct, it is a byproduct of an adaptation. Even the ELM, the hypothetical exapted learning mechanism, is an evolved learning mechanism, though used outside its natural domain.

We group the issues raised in the commentaries into five major sections. In the first, section R1, we consider some of the antecedents to dynamic systems (DS) in psychology, biology, anthropology, and primatology and note the key changes that have occurred in DS over the past ten years. Next, in section R2, we explain the ways in which co-regulation differs markedly from interactional synchrony, focusing in particular on the creation of meaning inherent in co-regulated communication. The following section (R3) clarifies the challenge that DS poses to Cartesian assumptions about the nature of communication and contrasts this position with behaviorism. In the next section (R4) we reject the notion that IP and DS may be, in fact, compatible paradigms. Finally, we explain the exciting future we envision for using DS to facilitate consideration of evolutionary questions, particularly those concerning the comparative evolutionary development of socio-emotional dynamics between partners (section R5).

Handaxe morphology is thought to be the first example of the imposition of arbitrary form. Handaxes may thus inform researchers about shared mental templates and evolving cognitive abilities. However, many factors, not related to changes in cognition (e.g., material type, function, resharpening processes), influence handaxe shape over time and space. Archaeologists must control for these factors before making inferences concerning cognition.

Altruism can be understood in terms of traditional principles of reinforcement if an outcome that is beneficial to another person reinforces the behavior of the actor who produces it. This account depends on a generalization of reinforcement across persons and might be more amenable to experimental investigation than the one proposed by Rachlin.

Adaptationist explanations for well-known phenomena are of limited value to psychological science. To be truly useful, evolutionary psychological research programs must produce novel discoveries about contemporary cognitive and behavioral processes. The concept of special design is especially useful. Even if special design cannot be convincingly demonstrated, rigorous attempts to meet this evidentiary standard can produce novel scientific contributions.

We agree with the critique of the Residual Normality assumption. Moreover, we challenge monolithic views of functional normality. Throughout life, development and adaptation require variations in cortical functional circuitry within and across individuals. We propose the principle of “coconstructed functionality” which maintains that brain-behavior functional correspondences are dynamically coproduced by neurobiological, experiential, and contextual processes.

The two modes of visual processing “localizing” versus “identifying” as expressed by four authors in 1967 are more encompassing than the “two visual systems” dichotomies posed by later theorists. Norman's view of parietal cortex functions of vision seems much too narrow.

I argue that Norman's thesis works in sofaras one is prepared to be lax about the alleged congruency between “ecological” and “dorsal,” and unconcerned by the results of recent studies showing that grasping movements are subject to the same geometric distortion illusions as perceptual judgements.

This commentary contests Wynn's diagnosis of the cognitive implications of the earliest stone tools and Acheulian tools. I argue that the earliest stone tools imply greater cognitive abilities than those of great apes, and that Acheulian tools imply more than the preoperational cognitive abilities Wynn suggests. Finally, I suggest an alternative adaptive scenario for the evolution of hominid cognitive abilities.

Any behavior belongs to innumerable overlapping types. Any adequate theory of emergence and retention of behavior, whether psychological or biological, must give us not only a general mechanism – reinforcement or selection, for example – but a reason why that mechanism applies to a particular behavior in terms of one of its types rather than others. Why is it as this type that the behavior is reinforced or selected?

This commentary discusses the logic of inferring modularity or the lack of modularity from observed patterns of developmental disorders.

Andrews et al. argue for adaptationism in cognitive research. However, the problem of evolvability brings into question the number of genes required for the evolution of cognitive mechanisms. Are there enough? Also, greater consideration should be given to alternative vicarious selection processes, which may produce cognitive mechanisms. Finally, identifying constraints with optimality arguments is more difficult than the authors think.

Why did Homo erectus begin to craft symmetric tools? A parsimonious account assumes that preference for symmetry is inherent in all visual systems. This preference can be explained by a broader preference for perceptual fluency. The perceptual fluency account does not assume that selection for mate health or the production of symbolic art is a prerequisite for symmetry preference.

Different developmental anomalies produce contrasting deficits in a single, integrated system. In a network that inflects regular and exception verbs correctly, a disproportionate deficit with exceptions occurs if connections are deleted, whereas a disproportionate deficit with regulars occurs when an auditory deficit impairs perception of the regular inflection. In general, contrasting deficits do not license the inference of underlying modularity.

The authors present a balanced critique of the adaptation/exaptation debate and specify some of the hard evidentiary criteria that are needed to advance our understanding of human evolution. Investigators must build more “special design” criteria into their theorizing and research. By documenting that certain traits meet these rigorous criteria, the evolutionary sciences will ultimately rest on a firmer theoretical foundation.

Whether or not the correspondence of dorsal stream functions to Gibsonian ecological psychology and the ventral stream functions to “constructivism” hold up, the overall goal of capturing a pragmatic realism should not be forgotten.

Altruism is traditionally encouraged by promoting a goal, for example, going to heaven. In contrast, Rachlin argues that altruistic behavior can be sufficiently reinforced by the abstract intrinsic reward that comes from maintaining an unbroken pattern of altruistic behavior. In my experience, there are very few people for whom this is true. For fellow atheists and anti-theists, I suggest an alternative.

Norman presents intriguing arguments in support of a mapping between ecological and constructivist visual cognition, on the one hand, onto the dorsal ventral dual route processing hypothesis, on the other hand. Unfortunately, his account is incompatible with developmental data on the functional emergence of the dorsal and ventral routes. We argue that it is essential for theories of adult visual cognition to take constraints from development seriously.

Reconstructing the evolution of cognition requires maximal extraction of information from very sparse data. The role that archaeology plays in this process is important, but strong empirical tests of plausible hypotheses are absolutely critical. Quantitative measures of symmetry must be devised, a much deeper understanding of nonhuman primate spatial cognition is needed, and a better understanding of brain/behavior relationships across species is necessary to properly ground these hypotheses.