Exploring the evolutionary connection between the rules of grammar and the grammar of physical action
What do assembling a piece of furniture, performing a complex dance routine, and constructing a grammatical sentence have in common? More than you might think.
For decades, linguists have largely viewed the human capacity for syntax—the rules for arranging words into sentences—as a unique, isolated module of the mind. However, a revolutionary perspective is gaining ground, one that connects the abstract rules of grammar to the physical grammar of action, all through the powerful lens of Darwinian evolution.
This article explores how researchers are now using the principles of "descent with modification" to build a bridge between the seemingly disparate domains of syntax and action planning. By breaking down both faculties into their primitive components, scientists are uncovering a shared evolutionary history that is not only reshaping our understanding of language but also revealing its deep connections to the neural circuits that guide our movements. This journey into comparative cognitive science suggests that the very structure of our language may be built upon an ancient foundation of how we interact with the world around us.
Brain regions like Broca's area and the basal ganglia are activated by both complex syntax and hierarchical action planning.
Both language and complex actions rely on nested, hierarchical organization rather than simple linear sequences.
The traditional stance in linguistics, heavily influenced by the work of Noam Chomsky, has long held that syntax is a uniquely human biological endowment1 . According to this view, the language faculty is a specialized module in the brain, with rules and representations that are distinct from other cognitive systems.
Proponents of this view argue that the "atoms" of syntax (words and their grammatical features) and its core computational mechanisms (like the operation called "Merge") have no true equivalent in the domain of motor control or action planning4 . From this perspective, comparing syntax to action is little more than a loose metaphor.
A new wave of cognitive scientists is challenging this isolationist view by applying Darwinian thinking to the mind. The key concept is "descent with modification"—the idea that new cognitive capacities do not appear out of thin air but evolve from pre-existing systems through gradual modification and adaptation4 .
From this vantage point, the human capacity for complex syntax may not be a sudden evolutionary miracle. Instead, it could have descended from, and been built upon, older neural circuits dedicated to planning and executing complex, hierarchical actions—like tool-making or foraging sequences2 4 .
| Argument | Explanation | Evolutionary Parallel |
|---|---|---|
| Shared Computation | The brain may reuse a single, powerful combinatorial operation for structuring both sentences and action plans4 . | Exaptation: A trait that evolved for one function (action sequencing) is co-opted for a new one (syntax). |
| Deep Homology | Underlying neural similarities may exist despite surface-level differences in what is being manipulated (words vs. movements)4 . | Common Ancestry: Different species share a genetic developmental program for a trait (e.g., the limb structure in vertebrates). |
| Evolvability | Building syntax from pre-existing action circuits is a more gradual, evolutionarily plausible path than a single, massive genetic mutation5 . | Gradualism: Complex traits evolve through a series of small, incremental steps. |
To move beyond theoretical debates, neuroscientists have designed clever experiments to test for a shared neural substrate. A crucial line of research involves comparing brain activity while subjects process different kinds of structures—both linguistic and non-linguistic.
Researchers design linguistic and non-linguistic stimuli with varying complexity5 .
Participants are placed in an fMRI scanner to measure brain activity.
Participants process sentences or action sequences while in the scanner.
Scientists compare activation patterns for hierarchical vs. flat structures.
The results of such experiments have been revealing. Studies have consistently shown that processing complex, hierarchical syntax activates a network involving the left Broca's area (a region in the frontal lobe) and the basal ganglia5 .
Crucially, when the same individuals process hierarchically complex action sequences, a similar neural network is engaged4 . This overlap is not merely coincidental. It suggests that Broca's area and the basal ganglia form a core circuit for building and processing hierarchical structures, regardless of whether those structures are made of words or of actions.
| Brain Region | Function in Syntax | Function in Action | Interpretation |
|---|---|---|---|
| Left Broca's Area (BA 44) | Building hierarchical phrase structures (e.g., embedding clauses)5 . | Planning and sequencing complex, multi-step actions4 . | A domain-general "structure builder" for hierarchy. |
| Basal Ganglia | Involved in the procedural memory of syntactic rules and sequencing words5 . | Critical for motor control, habit learning, and sequencing movements4 . | A key node for sequencing elements in both domains. |
| Right Fusiform Gyrus (BA 37) | Active in processing simple, ancestral forms like metaphorical compounds (e.g., "scatterbrain")5 . | Associated with object and face recognition; may link naming to identity. | May represent an older pathway for flat, non-hierarchical combination. |
To conduct the groundbreaking research that connects syntax, action, and evolution, scientists rely on a sophisticated toolkit. The table below details some of the essential "research reagents" and methods used in this field.
| Tool/Method | Function | Role in the Investigation |
|---|---|---|
| fMRI (functional Magnetic Resonance Imaging) | Measures brain activity by detecting subtle changes in blood flow. | The primary tool for non-invasively locating which brain networks are active during syntax and action tasks5 . |
| fTCD (functional Transcranial Doppler Ultrasound) | Measures blood flow velocity in major brain arteries, providing a portable measure of lateralized brain activity. | Used in studies, for example, to show shared lateralization patterns for language and tool-making4 . |
| Theoretical Syntax Frameworks (e.g., Minimalism) | Provides a precise, formal description of the components and operations of grammar (e.g., Merge, hierarchical phrases). | Allows researchers to make specific, testable predictions about what the brain should be doing when processing different syntactic structures5 . |
| EEG (Electroencephalography) | Records the brain's electrical activity with high temporal precision from the scalp. | Ideal for tracking the real-time dynamics of sentence processing and action observation, pinpointing when processes occur. |
| Evolutionary Proxies ("Living Fossils" of Language) | Identifies simple, flat structures in modern languages (e.g., small clauses, compounds) as models of ancestral syntax5 . | Provides a testable window into earlier evolutionary stages of language, allowing for comparison with more complex syntax. |
"The neural machinery that once orchestrated the precise strike of a toolmaker is, in a very real sense, the same machinery that now allows us to craft a complex sentence."
How might this shared neural hardware have evolved? The leading hypothesis is the "cognitive niche" theory. Our ancestors filled a unique ecological role by manipulating their environment through causal reasoning and social cooperation2 . This involved:
Creating tools requires multi-step, hierarchical plans, exercising the cognitive capacity for structured action.
Coordinated hunting and food sharing required planned, sequenced behaviors among individuals.
Simple stringing of words without hierarchical embedding; relies on order (e.g., agent-action-patient)5 .
Example: "Cat chase mouse." (interpretation relies on word order)
Neural Correlate: Likely distributed, older temporal and parietal regions.
Full, recursive embedding of phrases within phrases, enabled by functional words and morphemes (e.g., tense, agreement)5 .
Example: "The fact that he is leaving surprises me." (clause embedded inside a noun phrase)
Neural Correlate: Enhanced Broca's area-Basal Ganglia circuit, with increased neuronal connectivity5 .
The investigation into the link between syntax and action, guided by Darwinian thinking, is dismantling the old view of the mind as a collection of isolated modules.
Instead, it paints a picture of a brain that builds new, dazzling capacities—like language—by creatively reusing and refining ancient evolutionary tools. The neural machinery that once orchestrated the precise strike of a toolmaker is, in a very real sense, the same machinery that now allows us to craft a complex sentence.
This research has profound implications. It not only illuminates the origins of our species' most distinctive trait but also provides a new framework for understanding disorders of language and movement. It suggests that by studying the evolutionary roots of our cognition, we can better understand the very structure of human thought itself, revealing a deep and elegant unity between the hand, the brain, and the word.
Language did not emerge as a completely new faculty but evolved from pre-existing cognitive structures for action planning.
Understanding this connection provides new avenues for studying language disorders and their relationship to motor deficits.