978–0–19–955327–304-Sciullo-c04 Di-Sciullo (Typeset by SPi, Chennai) 65 of 99 May 10, 2010 13:46 OUP UNCORRECTED PROOF – FIRST PROOF, 10/5/2010, SPi 4 Syntax Facit Saltum Redux: Biolinguistics and the Leap to Syntax ROBERT C. BERWICK Ihavebeenastonishedhowrarelyanorgancanbenamed,towardswhichnotransi- tional grade is known to lead. The truth of this remark is indeed shown by that old canon in natural history of Natura non facit saltum. We meet with this admission in the writings of almost every experienced naturalist; or, as Milne Edwards has well expressed it, nature is prodigal in variety, but niggard in innovation. Why, on the theory of Creation, should this be so? . Why should not Nature have taken a leap from structure to structure? On the theory of natural selection, we can clearly understand why she should not; for natural selection can act only by taking advantage of slight successive variations; she can never take a leap, but must advance by the shortest and slowest steps. (Darwin 1859: 194) 4.1 Introduction: Language, Biology, and the Evolution–Language Gaps For hundreds of years, long before Darwin’s publication of Origin of Species (1859)andhisDescent of Man (1871)thatexplicitlybroughtlanguageintothe fold of modern evolutionary thinking, the evolution of language has captured the imagination of biologists and linguists both. Among many evolution- ary puzzles, one that stands out is the obvious discontinuity between the human species and all other organisms: language is evidently unique to the human lineage—being careful here to define language properly as distinct This research was supported by NSF grant 9217041-ASC and ARPA under the HPCC program. Noam Chomsky, Samuel Epstein, Anna-Maria Di Sciullo, Charles Yang, and Morris Halle provided many valuable comments; all remaining errors are our own. 978–0–19–955327–304-Sciullo-c04 Di-Sciullo (Typeset by SPi, Chennai) 66 of 99 May 10, 2010 13:46 OUP UNCORRECTED PROOF – FIRST PROOF, 10/5/2010, SPi 66 Robert Berwick from general communication, a matter addressed in Berwick and Chomsky (this volume) and considered further below. Such gaps, or evolutionary novelties, have always posed a challenge to classical Darwinian analysis, since that theory is grounded fundamentally on the notion of gradualism—incrementally fine steps leading from a trait’s pre- cursor, with adaptive, functioning intermediates at every step along the evolu- tionary path, ultimately culminating in an “organ of extreme complexity and perfection,” as with the vertebrate eye. Add one extra layer of light-sensitive membrane, so the argument goes, and an eye’s photon-trapping improves by a fractional percent—a smooth incline with no jumps or surprises. Indeed Dar- win himself devoted considerable effort in Origin to analyzing precisely this problem with this assumption (Chapter VI, “Organs of extreme perfection”), using the evolution of the eye as his make-or-break case study for his gradualist model, the very heart and soul of the theory itself, since, as he himself insists, “If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down” (1859: 189): To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real. (1859: 186) From this perspective, human language seems to be exactly the kind of unwanted biological surprise Darwin sought to avoid. Indeed, it apparently stands squarely as a counter-example to his entire theory of evolution via descent with modification, at least if we are to take Darwin at his word. Perhaps that is why ever since Darwin nearly all researchers seem to abhor even the slightest hint of a non-gradual, non-adaptationist account of human language evolution. It is perhaps worth recollecting that this picture of evolution-as-minute- accumulation of small changes was not always so strongly embraced. As the evolutionary theorist Allan Orr notes in a recent review (2005), in the late nineteenth and early twentieth centuries, Mendelians like William Bateson argued that the ‘micromutational’ view was simply a path of least effort: 978–0–19–955327–304-Sciullo-c04 Di-Sciullo (Typeset by SPi, Chennai) 67 of 99 May 10, 2010 13:46 OUP UNCORRECTED PROOF – FIRST PROOF, 10/5/2010, SPi Biolinguistics and the Leap to Syntax 67 “By suggesting that the steps through which an adaptive mechanism arises are indefinite and insensible, all further trouble is spared. While it could be said that species arise by an insensible and imperceptible process of variation, there was clearly no use in tiring ourselves by trying to perceive that process. This labor-saving counsel found great favor” (Bateson 1909). The gradualist position became the dominant paradigm in the field in the 1930s via the ana- lytical unification marrying Mendelism to Darwinism forged by R. A. Fisher, S. Wright, and J. B. S. Haldane, dubbed the “Modern Synthesis:” on this view, micro-mutational particulate events—tiny changes, perhaps at the level of single nucleotides (the DNA “letters” Adenine, Thymine, Guanine, and Cyto- sine), and correspondingly small steps in allele (gene variant) frequencies— comprise the bulk of evolutionary change. The Modern Synthesis too suggests that a Big-Bang emergence of language might be quite unlikely. How then can one reconcile evolutionary theory’s Modern Synthesis with the apparent discontinuity, species-specificity, and distinctive syntactic com- petence of human language? A familiar line of thinking simply denies that agapexistsatall:otherhominidsalsopossesshumansyntacticabilities. A second position embraces the Modern Synthesis and rejects discontinu- ity, asserting that all the particular properties of human language have been specifically selected for as directly adaptive, with small gradual changes lead- ing from non-language using ancestors to the present, a position perhaps most strongly advocated by Pinker and Bloom (1990). Other researchers deny that there are properties proprietary to human syntax, instead grounding them on principles of general purpose cognition, like those found in con- nectionism (Rummelhart and McClelland 1987). Still other approaches call for development from a proto-language to full language (Bickerton 1990). Perhaps the only proposals made previously that avoid an outright appeal to gradualism are those that involve exaptation in the sense of Gould and Vrba (1982), or genetic draft (Gillespie 1991)—that human language hitch- hiked on the back of a related, already adaptively advantageous cognitive subsystem, such as motor-gesture articulation, hierarchical tool-making, or social grooming. While these last approaches remain possibilities within a classical gradualist framework, they all focus on some external aspect of language-as-communication, rather than internal syntax tout court,amat- ter discussed elsewhere (Berwick and Chomsky, this volume). Berwick and Chomsky note that all recent relevant biological and evolutionary research leads to the conclusion that the process of externalization is secondary, sub- sequent to conceptualization and the core principles of human syntax. If this conclusion is on the right track, we are left with the same puzzling gap as before. 978–0–19–955327–304-Sciullo-c04 Di-Sciullo (Typeset by SPi, Chennai) 68 of 99 May 10, 2010 13:46 OUP UNCORRECTED PROOF – FIRST PROOF, 10/5/2010, SPi 68 Robert Berwick Besides this unsettling discontinuity, human language poses a second chal- lenging gap, a classic and also familiar biological one: how to bridge between agenotypeandaphenotype,inthiscaseperhapsthemostcomplexbehav- ioral phenotype we know. Linguistics has cast natural language’s intricate and ultimately behavioral “form that shows” (its phenotype) at an abstract level, far removed from language’s computational and biological “inner form” or genotype. Linguistic science’s successful program over the past fifty years has resulted in perhaps the richest description of a human genotype-to-phenotype mapping that we know of—the initial substrate for human language and how language develops in an individual. However, until recently progress at bridging from the language genotype to phenotype has been difficult. In part this is because we simply do not know much about the human language genotype, and we often run aground by misidentifying the language phenotype with communication, as mentioned above. Further, the gulf separating computation, biology, and language has been equally long-standing—in large measure resulting from the abstraction gap between linguistic and biological description: we do not expect to literally find a “passive grammar rule” inside a person’s head. The history of the field here from Fodor, Bever,