The shared circuits model (SCM) is a bold attempt to explain how humans make sense of action, at different levels. In this commentary we single out five concerns: (1) the lack of a developmental account, (2) the absence of double-dissociation evidence, (3) the neglect of joint attention and joint action, (4) the inability to explain discrete emotion perception, and (5) the lack of predictive power or testability of the model. We conclude that Hurley's model requires further work before it could be seen as an improvement over earlier models.

This commentary questions the general assumptions concerning the cognitive value of analogical reasoning on which the argument developed by Leech et al. appears to rest. In order to better assess the findings of their meta-analysis, it shifts the perspective from development to evolution, and frames their “how” concern within a broader “why” issue.

Christiansen & Chater (C&C) argue persuasively that Universal Grammar (UG) could not have arisen through evolutionary processes. I provide additional suggestions to strengthen the argument against UG evolution. Further, I suggest that C&C's solution to the logical problem of language evolution faces several problems. Widening the focus to mechanisms of general cognition and inclusion of animal communication research might overcome these problems.

The theory of psychosis and autism as diametrical disorders offers a tractable and testable view of normal and abnormal human cognitive variation as a function of opposing traits grouped by their selection for maternal and paternal reproductive fitness. The theory could be usefully rooted and developed with reference to the lower-level perceptual and attentional phenomena from which social cognitive modules are developmentally refined.

The contrast Rips et al. draw between “bottom-up” and “top-down” approaches to understanding the origin of the capacity for representing natural number is a false dichotomy. Its plausibility depends upon the sketchiness of the authors' own proposal. At least some of the proposals they characterize as bottom-up are worked-out versions of the very top-down position they advocate. Finally, they deny that the structures that these putative bottom-up proposals consider to be sources of natural number are even precursors of concepts of natural number. This denial depends upon an idiosyncratic, and mistaken, idea of what a precursor is.

Seemingly small changes in brain organization can have revolutionary consequences for function. An example is evolution's application of the primate action-planning mechanism to the management of communicative sequences. When feedback from utterances reaches the brain again through a mechanism that evolved to monitor action sequences, it makes another pass through the brain, amplifying the human power of thinking.

Despite its strengths, Leech et al.'s model fails to address the important benefits that derive from self-explanation and task feedback in analogical reasoning development. These components encourage explicit, self-reflective processes that do not necessarily link to knowledge accretion. We wonder, therefore, what mechanisms can be included within a connectionist framework to model self-reflective involvement and its beneficial consequences.

Differentiating self from other has been investigated at the neural level, and its incorporation into the model proposed Hurley is necessary for the model to be complete. With an emphasis on the feed-forward model in layer 2, we examine the role that self and other disruptions, including auditory verbal hallucinations (AVHs), may have in expanding the model proposed by Hurley.

Christiansen & Chater's (C&C's) arguments share with memetics the ideas that language is an evolving organism and that brain capacities shape language by influencing the fitness of memes, although memetics also claims that memes in turn shape brains. Their rejection of meme theory is based on falsely claiming that memes must be consciously selected by sighted watchmakers.

Crespi & Badcock (C&B) present an appealing and parsimonious synthesis arguing that schizophrenia and autism are differentially regulated by maternal versus paternal genomic imprinting, respectively. We argue that animal models related to schizophrenia and autism provide a useful platform to explore the mechanisms outlined by C&B. We also note that schizophrenia and autism share certain risk factors such as advanced paternal age. Apart from genomic imprinting, copy number variants related to advanced paternal age may also contribute to the differential trajectory of brain development associated with autism and schizophrenia.

Rips et al.'s analyses have boosted the plausibility of proposals that the human mind embodies some critical properties of natural numbers. I suggest that such proposals can be further evaluated by infant studies, neuropsychological data, and evolution-based considerations, and additionally, that Rips et al.'s model may need to be modified in order to more completely reflect infants' quantitative abilities.

Penn et al. do not demonstrate Darwin made a mistake, because they largely ignore the semantics underlying the meanings of “degree” and “kind.” An analysis based on the work of Mortimer Adler shows such terminology conflates at least three different meanings of “kind,” only one of which challenges Darwin – and one which the authors almost certainly would reject.

Languages emerge in response to the negotiation of shared meaning in social groups, where transparency of grammar is necessitated by demands of communication with relative strangers needing to consult on a wide range of topics (Ragir 2002). This communal exchange is automated and stabilized through activity-dependent fine-tuning of information-specific neural connections during postnatal growth and social development.

Leech et al. make two proposals: that relational priming is central to analogy, and that relations between objects are best represented as transformations of those objects. Although their account of analogy as relational priming is a useful contribution to our understanding of analogical development, in this commentary I show that relations in general cannot be represented by transformations.

Crespi & Badcock (C&B) provide a novel hypothesis outlining a role for imprinted genes in mediating brain functions underlying social behaviours. The basic premise is that maternally expressed genes are predicted to promote hypermentalistic behaviours, and paternally expressed genes hypomentalistic behaviours. The authors provide a detailed overview of data supporting their ideas, but as we discuss, caution should be applied in interpreting these data.

The target article says surprisingly little about the possible role of shared circuits in language and communication. This commentary considers how they might contribute to linguistic communication, particularly during dialogue. We argue that shared circuits are used to promote alignment between linguistic representations at many levels and to support production-based emulation of linguistic input during comprehension.

The confounding effects of heterogeneity in biological psychiatry and psychiatric genetics have been widely discussed in the literature. We suggest an approach in which heterogeneity may be put to use in hypothesis testing, and may find application in evaluation of the Crespi & Badcock (C&B) imprinting hypothesis. Here we consider three potential sources of etiologic subtypes for analysis.

We address the claim that nonhuman animals do not represent unobservable states, based on studies of physical cognition by rooks and social cognition by scrub-jays. In both cases, the most parsimonious explanation for the results is counter to the reinterpretation hypothesis. We suggest that imagination and prospection can be investigated in animals and included in models of cognitive architecture.

In their target article, Rips et al. have presented the view that there is no necessary dependency between natural numbers and internal magnitude. However, they do not give enough weight to neuroimaging and neuropsychological studies. We provide evidence demonstrating that the acquisition of natural numbers depends on magnitude representation and that natural numbers develop from a general magnitude mechanism in the parietal lobes.

Six questions are posed that are really specific versions of this question: How can Leech et al.'s system be extended to handle adult-level analogies that frequently combine concepts from semantically distant domains sharing few relational labels and that involve the production of abstractions? It is Leech et al. who stress development; finding such an extension would seem to have to be high on their priority list.