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ScienceWeek
ANTHROPOLOGY: ON THE ORIGINS OF HUMAN LANGUAGE
The following points are made by Gary F. Marcus (Nature 2004 431:745):
1) If, as Francois Jacob argued, evolution is like a tinkerer who builds something new by using whatever is close at hand, then from what is the human capacity for language made? Most accounts of the evolution of language have focused on characterizing changes that are internal to the language system. Were the earliest forms of language spoken or (like sign language) gestured? Did language arise suddenly? Or did it emerge gradually, progressing step by step from a simple one-word "protolanguage" (limited to brief comments about the "here and now") into a more complex system that combined individual words into structured meaningful sentences encompassing the future, the past and the possible -- as well as the concrete present? Regardless of how these questions are resolved, if we seek the ultimate origins of language, we also need to look further back, beyond the first protolinguistic systems, to whatever prelinguistic systems may have preceded any form of language.
2) Possible prelinguistic precursors might include systems for planning or sequencing complex events, categorization, automating repetitive actions, and representing space and time. In each case, there are parallels between candidate prelinguistic cognitive (or motor) precursors and systems found in language. For example, many animals are able to construct mental maps for navigation, and all known languages draw heavily on spatial metaphors. Thus, it is tempting to conclude that machinery for the mental representation of space plays some role in -- or is at the very least available to -- the machinery for language.
3) But parallels alone are not enough to establish shared lineage between two systems -- they could instead represent convergent (independent) evolution. For example, a language system could have evolved its own machinery for automating repeated tasks, independent of pre-existing machinery for automatizing other cognitive functions. A more telling way of establishing prelinguistic ancestry could come from evolutionary contrivances, properties of language that existed not because of some selective advantage, but simply because they have descended from ancestral systems evolved for other purposes. Just as the panda's thumb is not a true digit, but a modified sesamoid bone pressed into service for gripping bamboo, some properties of our capacity for language may be better understood not as optimal solutions to a system for communication, but as cobbled-together remnants of ancestral cognitive systems.
4) In language, one good candidate comes from the study of memory. According to an optimal design, if the capacity for understanding language were evolved from scratch, it would be possible to reliably retrieve individual bits of syntactic structure on the basis of their location in a hierarchical structure, independently of their content -- as in most digital computers. Instead, human language systems seem to rely on "content-addressable" memory, a form of memory -- widespread in the vertebrate world and with an apparently ancient evolutionary source -- that retrieves information directly on the basis of its content, rather than through location. Unlike a computer's binary-tree structure, content-dependent memory in mammalian brains is subject to degradation over time and to interference between similar or intervening items.
5) Human speakers are thus less likely to resolve the relation between "admired" and "the newspaper" in a sentence such as: "It was the newspaper that was published by the undergraduates that the editor admired," than in the briefer sentence "It was the newspaper that the editor admired." In languages such as English that lack rich case-marking, in most cases listeners can correctly interpret only two levels of embedding, not because of a strict limit on the size of representable binary trees, but because similar items become confused in memory.(1-5)
References (abridged):
1. Christiansen, M. H. & Kirby, S. Language Evolution (Oxford University Press, 2003)
2. Gould, S. J. The Panda's Thumb (Norton, 1980)
3. Jackendoff, R. Foundations of Language: Brain, Meaning, Grammar, Evolution (Oxford University Press, 2002)
4. Marcus, G. F. The Birth of the Mind (Basic Books, 2004)
5. McElree, B. et al. J. Mem. Language 48, 67-91 (2003)
Nature http://www.nature.com/nature
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Related Material:
LANGUAGE GRAMMAR PROPOSED TO HAVE EVOLVED BY NATURAL SELECTION
Notes by ScienceWeek:
Language is considered a quintessentially human trait, and attempts to shed light on the evolution of human language have come from diverse areas including studies of primate social behavior, the diversity of existing human languages, the development of language in children, the genetic and anatomical correlates of language competence, and theoretical studies of cultural evolution, learning, and lexicon formation. One major question is whether human language is a product of evolution or a side-effect of a large and complex brain evolved for non-linguistic purposes.
The following points are made by M.A. Nowak and D.C. Krakauer (Proc. Nat. Acad. Sci. 1999 96:8028):
1) The authors provide an approach to language evolution based on evolutionary game theory, the authors exploring the ways in which protolanguage can evolve in a nonlinguistic society and how specific signals can become associated with specific objects.
2) The authors argue that grammar originated as a simplified rule system that evolved by natural selection to reduce mistakes in communication, and they suggest their theory provides a systematic approach for thinking about the origin and evolution of human language.
Proc. Nat. Acad. Sci. http://www.pnas.org
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Related Material:
ON THE GESTURAL ORIGINS OF HUMAN LANGUAGE
Notes by ScienceWeek:
A view currently held by many anthropologists and linguistics researchers is that the remarkable flexibility of human language is achieved at least in part through the human invention of grammar, a recursive set of rules that allows the generation of sentences of any desired complexity. The linguist Noam Chomsky has attributed this to a unique human endowment termed "universal grammar", with Chomsky suggesting that all human languages are variants of this fundamental endowment.
The following points are made by Michael C. Corballis (American Scientist Mar-Apr 1999 87:138):
1) There is little doubt that the great apes (orangutan, gorilla, chimpanzee) (and perhaps other species such as dolphins) can use symbols to represent actions and objects in the real world, but these animals lack nearly all the other ingredients of true language.
2) Since the common ancestor of human beings and chimpanzees lived approximately 5 million years ago, it is a reasonable inference that grammatical language must have evolved in the hominid line (i.e., the line of human primates) at some point following the split from the line that led to the modern chimpanzee. There has been much disagreement as to when this might have happened.
3) One major view holds that it is impossible to conceive of grammar as having been formed incrementally; grammar therefore must have evolved as a single catastrophic event, probably late in hominid evolution. But many researchers hold a contrary view, that language evolved gradually, shaped by natural selection, and that the cognitive prerequisites of language are already present in the great apes and antedated the split of our hominid ancestors from the chimpanzee line, probably by several million years.
4) The author suggests that at least a partial reconciliation of these alternative perspectives may be that language emerged not from vocalization, but from manual gestures, and switched to a vocal mode relatively recently in hominid evolution, perhaps with the emergence of Homo sapiens. This is an old idea, apparently first suggested by Condillac in the 17th century, but argument in its favor has continued to grow.
5) The author points out that there are countless different sign languages invented by deaf people all over the world, and there is little doubt that these are genuine languages with fully developed grammars. The spontaneous emergence of sign languages among deaf communities everywhere confirms that gestural communication is as natural to the human condition as is spoken language. Indeed, children exposed from an early age only to sign language go through the same basic stages of acquisition as children learning to speak, including a stage when they "babble" silently in sign.
6) The authors proposes the following speculative scenario concerning the historical development of human language:
a) 6 or 7 million years ago: Simple gestures first anticipated more complex forms of communication, shortly after the human line diverged from the great apes. At this stage vocalizations served only as emotional cries and alarm calls.
b) Approximately 5 million years ago: With the advent of bipedalism, a more sophisticated form of gesturing involving hand signals may have evolved among the early hominids now labelled as "Australopithecus".
c) Approximately 2 million years ago: In association with the increasing brain size of the genus Homo, hand gestures became fully syntactic (i.e., with syntax; with ordered arrangements), but vocalizations also became prominent.
d) 100,000 years ago: Homo sapiens switched to speech as its primary means of communication, with gestures now playing a secondary role.
e) Modern times: The development of telecommunication now permits the routine use of spoken language in the complete absence of hand gestures, but even so, many people find themselves gesturing when they speak on the telephone.
7) Concerning the question of what it was that enabled our species to prevail over other large-brained hominids, the author concludes: "Perhaps the most plausible answer is that they prevailed because of superior technology. But that technology might have resulted, not from an increase in brain size or intelligence, but from a switch from manual to vocal language that allowed them to use their hands for the manufacture of tools and weapons and their voices for instruction."
American Scientist http://www.americanscientist.org
ScienceWeek http://scienceweek.com
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