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2002年，Hauser（比较有争议的前哈佛教授）、Chomsky和Fitch在《科学》杂志发表了一篇语言学论文，论述人类语言官能（语言是人类大脑中的一个“器官”），立刻轰动全球。时至今日，这篇论文已被引用4000多次，成为了语言学的经典文章。 受到微信文章的字数限制，今天推送的这篇文章，在力求保证主要内容的情况下删去了部分小节。 读完这篇英文文章，你会明白： 1. 什么是“语言官能”； 2. 动物有没有语言； 3. 什么是I-language； 4. FLN、FLB分别是什么； 5. 为什么说生物学和语言学的交叉研究是一个趋势。
The faculty of language: what is it, who has it, and how did it evolve? If a martian graced our planet, it would be struck by one remarkable similarity among Earth's living creatures and a key difference. Concerning similarity, it would note that all living things are designed on the basis of highly conserved developmental systems that read an (almost) universal language encoded in DNA base pairs. As such, life is arranged hierarchically with a foundation of discrete, unblendable units (codons, and, for the most part, genes) capable of combining to create increasingly complex and virtually limitless varieties of both species and individual organisms. In contrast, it would notice the absence of a universal code of communication (Fig. 1). If our martian naturalist were meticulous, it might note that the faculty mediating human communication appears remarkably different from that of other living creatures; it might further note that the human faculty of language appears to be organized like the genetic code—hierarchical, generative, recursive, and virtually limitless with respect to its scope of expression. With these pieces in hand, this martian might begin to wonder how the genetic code changed in such a way as to generate a vast number of mutually incomprehensible communication systems across species while maintaining clarity of comprehension within a given species. The martian would have stumbled onto some of the essential problems surrounding the question of language evolution, and of how humans acquired the faculty of language. At least three theoretical issues cross-cut the debate on language evolution. One of the oldest problems among theorists is the “shared versus unique” distinction. Most current commentators agree that, although bees dance, birds sing, and chimpanzees grunt, these systems of communication differ qualitatively from human language. In particular, animal communication systems lack the rich expressive and open-ended power of human language (based on humans' capacity for recursion). The evolutionary puzzle, therefore, lies in working out how we got from there to here, given this apparent discontinuity. A second issue revolves around whether the evolution of language was gradual versus saltational; this differs from the first issue because a qualitative discontinuity between extant species could have evolved gradually, involving no discontinuities during human evolution. Finally, the “continuity versus exaptation” issue revolves around the problem of whether human language evolved by gradual extension of preexisting communication systems, or whether important aspects of language have been exapted away from their previous adaptive function (e.g., spatial or numerical reasoning, Machiavellian social scheming, tool-making). Researchers have adopted extreme or intermediate positions regarding these basically independent questions, leading to a wide variety of divergent viewpoints on the evolution of language in the current literature. There is, however, an emerging consensus that, although humans and animals share a diversity of important computational and perceptual resources, there has been substantial evolutionary remodeling since we diverged from a common ancestor some 6 million years ago. The empirical challenge is to determine what was inherited unchanged from this common ancestor, what has been subjected to minor modifications, and what (if anything) is qualitatively new. The additional evolutionary challenge is to determine what selectional pressures led to adaptive changes over time and to understand the various constraints that channeled this evolutionary process. Answering these questions requires a collaborative effort among linguists, biologists, psychologists, and anthropologists. One aim of this essay is to promote a stronger connection between biology and linguistics by identifying points of contact and agreement between the fields. Although this interdisciplinary marriage was inaugurated more than 50 years ago, it has not yet been fully consummated. We hope to further this goal by, first, helping to clarify the biolinguistic perspective on language and its evolution (2–7). We then review some promising empirical approaches to the evolution of the language faculty, with a special focus on comparative work with nonhuman animals, and conclude with a discussion of how inquiry might profitably advance, highlighting some outstanding problems. Defining the Target: Two Senses of the Faculty of Language The word “language” has highly divergent meanings in different contexts and disciplines. In informal usage, a language is understood as a culturally specific communication system (English, Navajo, etc.). In the varieties of modern linguistics that concern us here, the term “language” is used quite differently to refer to an internal component of the mind/brain (sometimes called “internal language” or “I-language”). We assume that this is the primary object of interest for the study of the evolution and function of the language faculty. However, this biologically and individually grounded usage still leaves much open to interpretation (and misunderstanding). For example, a neuroscientist might ask: What components of the human nervous system are recruited in the use of language in its broadest sense? Because any aspect of cognition appears to be, at least in principle, accessible to language, the broadest answer to this question is, probably, “most of it.” Even aspects of emotion or cognition not readily verbalized may be influenced by linguistically based thought processes. Thus, this conception is too broad to be of much use. We therefore delineate two more restricted conceptions of the faculty of language, one broader and more inclusive, the other more restricted and narrow (Fig. 2). Faculty of language—broad sense (FLB). FLB includes an internal computational system (FLN, below) combined with at least two other organism-internal systems, which we call “sensory-motor” and “conceptual-intentional.” Despite debate on the precise nature of these systems, and about whether they are substantially shared with other vertebrates or uniquely adapted to the exigencies of language, we take as uncontroversial the existence of some biological capacity of humans that allows us (and not, for example, chimpanzees) to readily master any human language without explicit instruction. FLB includes this capacity, but excludes other organism-internal systems that are necessary but not sufficient for language (e.g., memory, respiration, digestion, circulation, etc.). Faculty of language—narrow sense (FLN). FLN is the abstract linguistic computational system alone, independent of the other systems with which it interacts and interfaces. FLN is a component of FLB, and the mechanisms underlying it are some subset of those underlying FLB. Others have agreed on the need for a restricted sense of “language” but have suggested different delineations. For example, Liberman and his associates (8) have argued that the sensory-motor systems were specifically adapted for language, and hence should be considered part of FLN. There is also a long tradition holding that the conceptual-intentional systems are an intrinsic part of language in a narrow sense. In this article, we leave these questions open, restricting attention to FLN as just defined but leaving the possibility of a more inclusive definition open to further empirical research. At a minimum, FLN includes the capacity of recursion. There are many organism-internal factors, outside FLN or FLB, that impose practical limits on the usage of the system. For example, lung capacity imposes limits on the length of actual spoken sentences, whereas working memory imposes limits on the complexity of sentences if they are to be understandable. Other limitations—for example, on concept formation or motor output speed—represent aspects of FLB, which have their own evolutionary histories and may have played a role in the evolution of the capacities of FLN. Nonetheless, one can profitably inquire into the evolution of FLN without an immediate concern for these limiting aspects of FLB. This is made clear by the observation that, although many aspects of FLB are shared with other vertebrates, the core recursive aspect of FLN currently appears to lack any analog in animal communication and possibly other domains as well. This point, therefore, represents the deepest challenge for a comparative evolutionary approach to language. We believe that investigations of this capacity should include domains other than communication (e.g., number, social relationships, navigation). Given the distinctions between FLB and FLN and the theoretical distinctions raised above, we can define a research space as sketched in Fig. 3. This research space identifies, as viable, problems concerning the evolution of sensory-motor systems, of conceptual-intentional systems, and of FLN. The comparative approach, to which we turn next, provides a framework for addressing questions about each of these components of the faculty of language. The Comparative Approach to Language Evolution The empirical study of the evolution of language is beset with difficulties. Linguistic behavior does not fossilize, and a long tradition of analysis of fossil skull shape and cranial endocasts has led to little consensus about the evolution of language (7,9). A more tractable and, we think, powerful approach to problems of language evolution is provided by the comparative method, which uses empirical data from living species to draw detailed inferences about extinct ancestors (3, 10–12). The comparative method was the primary tool used by Darwin (13, 14) to analyze evolutionary phenomena and continues to play a central role throughout modern evolutionary biology. Although scholars interested in language evolution have often ignored comparative data altogether or focused narrowly on data from nonhuman primates, current thinking in neuroscience, molecular biology, and developmental biology indicates that many aspects of neural and developmental function are highly conserved, encouraging the extension of the comparative method to all vertebrates (and perhaps beyond). For several reasons, detailed below, we believe that the comparative method should play a more central role in future discussions of language evolution. An overarching concern in studies of language evolution is with whether particular components of the faculty of language evolved specifically for human language and, therefore (by extension), are unique to humans. Logically, the human uniqueness claim must be based on data indicating an absence of the trait in nonhuman animals and, to be taken seriously, requires a substantial body of relevant comparative data. More concretely, if the language evolution researcher wishes to make the claim that a trait evolved uniquely in humans for the function of language processing, data indicating that no other animal has this particular trait are required. Testing Hypotheses About the Evolution of the Faculty of Language Hypothesis 1: FLB is strictly homologous to animal communication.This hypothesis holds that homologs of FLB, including FLN, exist (perhaps in less developed or otherwise modified form) in nonhuman animals (3, 10, 26). This has historically been a popular hypothesis outside of linguistics and closely allied fields, and has been defended by some in the speech sciences. According to this hypothesis, human FLB is composed of the same functional components that underlie communication in other species. Hypothesis 2: FLB is a derived, uniquely human adaptation for language. According to this hypothesis, FLB is a highly complex adaptation for language, on a par with the vertebrate eye, and many of its core components can be viewed as individual traits that have been subjected to selection and perfected in recent human evolutionary history. This appears to represent the null hypothesis for many scholars who take the complexity of language seriously (27,28). The argument starts with the assumption that FLB, as a whole, is highly complex, serves the function of communication with admirable effectiveness, and has an ineliminable genetic component. Because natural selection is the only known biological mechanism capable of generating such functional complexes [the argument from design (29)], proponents of this view conclude that natural selection has played a powerful role in shaping many aspects of FLB, including FLN, and, further, that many of these are without parallel in nonhuman animals. Although homologous mechanisms may exist in other animals, the human versions have been modified by natural selection to the extent that they can be reasonably seen as constituting novel traits, perhaps exapted from other contexts [e.g., social intelligence, tool-making (7, 30–32)]. Hypothesis 3: Only FLN is uniquely human. On the basis of data reviewed below, we hypothesize that most, if not all, of FLB is based on mechanisms shared with nonhuman animals (as held by hypothesis 1). In contrast, we suggest that FLN—the computational mechanism of recursion—is recently evolved and unique to our species (33,34). According to this hypothesis, much of the complexity manifested in language derives from complexity in the peripheral components of FLB, especially those underlying the sensory-motor (speech or sign) and conceptual-intentional interfaces, combined with sociocultural and communicative contingencies. FLB as a whole thus has an ancient evolutionary history, long predating the emergence of language, and a comparative analysis is necessary to understand this complex system. By contrast, according to recent linguistic theory, the computations underlying FLN may be quite limited. In fact, we propose in this hypothesis that FLN comprises only the core computational mechanisms of recursion as they appear in narrow syntax and the mappings to the interfaces. If FLN is indeed this restricted, this hypothesis has the interesting effect of nullifying the argument from design, and thus rendering the status of FLN as an adaptation open to question. Proponents of the idea that FLN is an adaptation would thus need to supply additional data or arguments to support this viewpoint. Recent work on FLN (4, 41–43) suggests the possibility that at least the narrow-syntactic component satisfies conditions of highly efficient computation to an extent previously unsuspected. Thus, FLN may approximate a kind of “optimal solution” to the problem of linking the sensory-motor and conceptual-intentional systems. In other words, the generative processes of the language system may provide a near-optimal solution that satisfies the interface conditions to FLB. Many of the details of language that are the traditional focus of linguistic study [e.g., subjacency, Wh- movement, the existence of garden-path sentences (4,44)] may represent by-products of this solution, generated automatically by neural/computational constraints and the structure of FLB—components that lie outside of FLN. Even novel capacities such as recursion are implemented in the same type of neural tissue as the rest of the brain and are thus constrained by biophysical, developmental, and computational factors shared with other vertebrates. Hypothesis 3 raises the possibility that structural details of FLN may result from such preexisting constraints, rather than from direct shaping by natural selection targeted specifically at communication. Insofar as this proves to be true, such structural details are not, strictly speaking, adaptations at all. This hypothesis and the alternative selectionist account are both viable and can eventually be tested with comparative data. Conclusions We conclude by making three points. First, a practical matter: Linguists and biologists, along with researchers in the relevant branches of psychology and anthropology, can move beyond unproductive theoretical debate to a more collaborative, empirically focused and comparative research program aimed at uncovering both shared (homologous or analogous) and unique components of the faculty of language. Second, although we have argued that most if not all of FLB is shared with other species, whereas FLN may be unique to humans, this represents a tentative, testable hypothesis in need of further empirical investigation. Finally, we believe that a comparative approach is most likely to lead to new insights about both shared and derived features, thereby generating new hypotheses concerning the evolutionary forces that led to the design of the faculty of language. Specifically, although we have said relatively little about the role of natural selection in shaping the design features of FLN, we suggest that by considering the possibility that FLN evolved for reasons other than language, the comparative door has been opened in a new and (we think) exciting way. Comparative work has generally focused on animal communication or the capacity to acquire a human-created language. If, however, one entertains the hypothesis that recursion evolved to solve other computational problems such as navigation, number quantification, or social relationships, then it is possible that other animals have such abilities, but our research efforts have been targeted at an overly narrow search space (Fig. 3). If we find evidence for recursion in animals, but in a noncommunicative domain, then we are more likely to pinpoint the mechanisms underlying this ability and the selective pressures that led to it. This discovery, in turn, would open the door to another suite of puzzles: Why did humans, but no other animal, take the power of recursion to create an open-ended and limitless system of communication? Why does our system of recursion operate over a broader range of elements or inputs (e.g., numbers, words) than other animals? One possibility, consistent with current thinking in the cognitive sciences, is that recursion in animals represents a modular system designed for a particular function (e.g., navigation) and impenetrable with respect to other systems. During evolution, the modular and highly domain-specific system of recursion may have become penetrable and domain-general. This opened the way for humans, perhaps uniquely, to apply the power of recursion to other problems. This change from domain-specific to domain-general may have been guided by particular selective pressures, unique to our evolutionary past, or as a consequence (by-product) of other kinds of neural reorganization. Either way, these are testable hypotheses, a refrain that highlights the importance of comparative approaches to the faculty of language. 全文、参考文献及脚注参见PDF版，下载地址：psych.colorado.edu/~kimlab/hauser.chomsky.fitch.science2002.pdf |
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