Language Evolution and Computation Bibliography

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

Human speech involves species-specific anatomy deriving from the descent of the tongue into the pharynx. The human tongue's shape and position yields the 1:1 oral-to-pharyngeal proportions of the supralaryngeal vocal tract. Speech also requires a brain that can ``reiterate''--freely reorder a finite set of motor gestures to form a potentially infinite number of words and sentences. The end points of the evolutionary process are clear. The chimpanzee lacks a supralaryngeal vocal tract capable of producing the ``quantal'' sounds which facilitate both speech production and perception and a brain that can reiterate the phonetic contrasts apparent in its fixed vocalizations. The traditional Broca-Wernicke brain-language theory is incorrect; neural circuits linking regions of the cortex with the basal ganglia and other subcortical structures regulate motor control, including speech production, as well as cognitive processes including syntax. The dating of the FOXP2 gene, which governs the embryonic development of these subcortical structures, provides an insight on the evolution of speech and language. The starting points for human speech and language were perhaps walking and running. However, fully human speech anatomy first appears in the fossil record in the Upper Paleolithic (about 50,000 years ago) and is absent in both Neanderthals and earlier humans.

TABLE OF CONTENTS
Preface
1. The Mark of Evolution
2. Primitive and Derived Features of Language
3. The Singularity of Speech
4. The Neural Bases of Language
5. Motor Control and the Evolution of Language
6. The Gift of Tongue
7. Linguistic Issues
8. Where We Might Go

The major ''contribution'' of generative grammar to cognitive science is negative. The hermetic disjuncture of linguistic research from biological principles and facts has influenced cognitive science. Linguists have followed the pied piper taking a different path from that pointed out by Charles Darwin. As Dobzhansky (1973) noted, ''Nothing in biology makes sense except in the light of evolution.'' The hermetic nature of much linguistic research is apparent even in phonology which must reflect biological facts concerning speech production. For example, studies dating back to 1928 show that tongue ''features'' do not specify vowel distinctions. However, the irrefutable findings of these cineradiographic and MRI studies are generally ignored by linguists. Chomsky's central premise, that syntactic ability derives from an innate ''Universal Grammar'' common to all human beings constitutes a strong biological claim. But if a UG genetically similar for all ''normal'' individuals existed, one of the central premises of Darwinian evolutionary biology, genetic variation would be false. Concepts and processes borrowed from linguistics such as ''modularity'' have impeded our understanding of brain-behavior relations. Some aspects of behavior are regulated in specific localized ''modules'' in the brain, but current research demonstrates that the neural architecture regulating human language is also implicated in motor control, cognition, and other aspects of behavior. The neural bases of enhanced human language are not separable from cognition and motor ability. The supposed unique aspect of syntax, its ''reiterative'' productivity, appears to derive from subcortical structures that play a part in neural circuits regulating motor control. Natural selection aimed at enhancing adaptive motor control ultimately yielded a basal ganglia ''sequencing engine'' that can produce a potentially infinite number of novel actions, thoughts , or ''sentences'' from a finite number of basic elements. Recent studies suggest that the human FOXP2 gene, which differs from similar regulatory genes in chimpanzees and other mammals, acts on the basal ganglia and other subcortical structures to confer enhanced human reiterative ability in domains as different as syntax and dancing. The probable date of the critical mutations on FOXP2 is coincident with the appearance of anatomically modern human beings about 150,000 to 200,000 years ago. Humans thus can create more complex sentences than chimpanzees, but has anyone ever seen an ape dancing?

The traditional theory equating the brain bases of language with Broca's and Wernicke's neocortical areas is wrong. Neural circuits linking activity in anatomically segregated populations of neurons in subcortical structures and the neocortex throughout the human brain regulate complex behaviors such as walking, talking, and comprehending the meaning of sentences. When we hear or read a word, neural structures involved in the perception or real-world associations of the word are activated as well as posterior cortical regions adjacent to Wernicke's area. Many areas of the neocortex and subcortical structures support the cortical-striatal-cortical circuits that confer complex syntactic ability, speech production, and a large vocabulary. However, many of these structures also form part of the neural circuits regulating other aspects of behavior. For example, the basal ganglia, which regulate motor control, are also crucial elements in the circuits that confer human linguistic ability and abstract reasoning. The cerebellum, traditionally associated with motor control, is active in motor learning. The basal ganglia are also key elements in reward-based learning. Data from studies of Broca's aphasia, Parkinson's disease, hypoxia, focal brain damage, and a genetically transmitted brain anomaly (the putative ``language gene,'' family KE), and from comparative studies of the brains and behavior of other species, demonstrate that the basal ganglia sequence the discrete elements that constitute a complete motor act, syntactic process, or thought process. Imaging studies of intact human subjects and electrophysiologic and tracer studies of the brains and behavior of other species confirm these findings. As Dobzansky put it, ``Nothing in biology makes sense except in the light of evolution'' (cited in Mayr, 1982). That applies with as much force to the human brain and the neural bases of language as it does to the human foot or jaw. The converse follows: the mark of evolution on the brains of human beings and other species provides insight into the evolution of the brain bases of human language. The neural substrate that regulated motor control in the common ancestor of apes and humans most likely was modified to enhance cognitive and linguistic ability. Speech communication played a central role in this process. However, the process that ultimately resulted in the human brain may have started when our earliest hominid ancestors began to walk.