It is widely assumed that human learning and the structure of human languages are intimately related. This relationship is frequently suggested to derive from a language-specific biological endowment, which encodes universal, but communicatively arbitrary, principles of language structure (a Universal Grammar or UG). How might such a UG have evolved? We argue that UG could not have arisen either by biological adaptation or non-adaptationist genetic processes, resulting in a logical problem of language evolution. Specifically, as the processes of language change are much more rapid than processes of genetic change, language constitutes a “moving target” both over time and across different human populations, and, hence, cannot provide a stable environment to which language genes could have adapted. We conclude that a biologically determined UG is not evolutionarily viable. Instead, the original motivation for UG – the mesh between learners and languages – arises because language has been shaped to fit the human brain, rather than vice versa. Following Darwin, we view language itself as a complex and interdependent “organism,” which evolves under selectional pressures from human learning and processing mechanisms. That is, languages themselves are shaped by severe selectional pressure from each generation of language users and learners. This suggests that apparently arbitrary aspects of linguistic structure may result from general learning and processing biases deriving from the structure of thought processes, perceptuo-motor factors, cognitive limitations, and pragmatics.

Sign languages provide direct evidence for the relation between human languages and the body that engenders them. We discuss the use of the hands to create symbols and the role of the body in sign language verb systems, especially in two quite recently developed sign languages, Israeli Sign Language and Al-Sayyid Bedouin Sign Language.

We agree that much of language evolution is likely to be adaptation of languages to properties of the brain. However, the attempt to rule out the existence of language-specific adaptations a priori is misguided. In particular, the claim that adaptation to “moving targets” cannot occur is false. Instead, the details of gene-culture coevolution in language are an empirical matter.

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.

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.

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.

Christiansen & Chater's (C&C's) argument rests on an assumption that convergent cultural evolution can produce similar (complex) behaviours in isolated populations. In this commentary, I describe how experiments recently carried out by Caldwell and colleagues can contribute to the understanding of such phenomena.

Evolutionary contingencies select organisms based on what they can do; brains and other evolved structures serve their behavior. Arguments that brains drive language structure get the direction wrong; with functional issues unacknowledged, interactions between central structures and periphery are overlooked. Evidence supports a peripherally driven central organization. If language modules develop like other brain compartments, then environmental consistencies can engender both structural and functional language units (e.g., the different phonemic, semantic, and grammatical structures of different languages).

Recognising that signed languages are true languages adds to the variety of forms that languages can take. Such recognition also allows one to differentiate those aspects of language that depend on the medium (voiced or signed) from those that depend on more cognitive aspects. At least some aspects of language, such as symbolic representation, time markers, and generativity, may derive from the communication of the products of mental time travel, and from the sharing of remembered past and planned future episodes.

Universal Grammar (UG) is indeed evolutionarily implausible. But if languages are just “adapted” to a large primate brain, it is hard to see why other primates do not have complex languages. The answer is that humans have evolved a specialized and uniquely human cognitive architecture, whose main function is to compute mappings between arbitrary signals and communicative intentions. This underlies the development of language in the human species.

Selection through iterated learning explains no more than other non-functional accounts, such as Universal Grammar (UG), why language is so well designed for communicative efficiency. It does not predict several distinctive features of language, such as central embedding, large lexicons, or the lack of iconicity, which seem to serve communication purposes at the expense of learnability.

Language is shaped by its environment, which includes not only the brain, but also the public context in which speech acts are effected. To fully account for why language has the shape it has, we need to examine the constraints imposed by language use as a sequentially organized joint activity, and as the very conduit for linguistic diffusion and change.

Meaning construction through language requires advanced mental operations also necessary for other higher-order, specifically human behaviors. Biological evolution slowly improved conceptual mapping capacities until human beings reached the level of double-scope blending, perhaps 50 to 80 thousand years ago, at which point language, along with other higher-order human behaviors, became possible. Languages are optimized to be driven by the principles and powers of double-scope blending.

Historical language change (“glossogeny”), like evolution itself, is a fact; and its implications for the biological evolution of the human capacity for language acquisition (“phylogeny”) have been ably explored by many contemporary theorists. However, Christiansen & Chater's (C&C's) revolutionary call for a replacement of phylogenetic models with glossogenetic cultural models is based on an inadequate understanding of either. The solution to their “logical problem of language evolution” lies before their eyes, but they mistakenly reject it due to a supposed “circularity trap.” Gene/;culture co-evolution poses a series of difficult theoretical and empirical problems that will be resolved by subtle thinking, adequate models, and careful cross-disciplinary research, not by oversimplified manifestos.

This commentary aims to highlight what exactly is controversial about the traditional Universal Grammar (UG) hypothesis and what is not. There is widespread agreement that we are not born “blank slates,” that language universals exist, that grammar exists, and that adults have domain-specific representations of language. The point of contention is whether we should assume that there exist unlearned syntactic universals that are arbitrary and specific to Language.

We propose that some aspects of language – notably intersubjectivity – evolved to fit the brain, whereas other aspects – notably grammar – co-evolved with the brain. Cladistic analysis indicates that common basic structures of both action and grammar arose in phylogeny six million years ago and in ontogeny before age two, with a shared prefrontal neural substrate. In contrast, mirror neurons, found in both humans and monkeys, suggest that the neural basis for intersubjectivity evolved before language. Natural selection acts upon genes controlling the neural substrates of these phenotypic language functions.

Christiansen & Chater (C&C) suggest that language is an organism, like us, and that our brains were not selected for Universal Grammar (UG) capacity; rather, languages were selected for learnability with minimal trial-and-error experience by our brains. This explanation is circular: Where did our brain's selective capacity to learn all and only UG-compliant languages come from?

That language is shaped to fit the human brain is close to the Chomskyan position. The target article by Christiansen & Chater (C&C) assumes an entity, “(the) language,” outside individual heads. What is the nature of this entity? Linguistic niche-construction and co-evolution of language and genes are possible, with some of what evolved being language-specific. Recent generative theory postulates much less than the old Universal Grammar (UG).

The claim that language is shaped by the brain is weakened by lack of clear specification of what necessary and sufficient properties the brain actually imposes. To account for human intellectual superiority, it is proposed that language did require special brain evolution (Deacon 1997), but that what evolved was a merely quantitative change – in representation space – rather than a radically new invention.

Neural circuits linking local operations in the cortex and the basal ganglia confer reiterative capacities, expressed in seemingly unrelated human traits such as speech, syntax, adaptive actions to changing circumstances, dancing, and music. Reiteration allows the formation of a potentially unbounded number of sentences from a finite set of syntactic processes, obviating the need for the hypothetical “Narrow Faculty of Language.”