Pinker, S. &
Bloom, P. (1990). Natural language and
natural selection. Behavioral and Brain Sciences 13 (4): 707-784.
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Language,
Evolution, Language
Acquisition, Natural Selection, Grammatical Theory, Biology of Language, Language Universals,
Psycholinguistics, Origin of Language
Many people have argued that the evolution of the human language faculty cannot be
explained by Darwinian natural selection. Chomsky and Gould have suggested that
language may have
evolved as the by-product of selection for other abilities or as a consequence
of as-yet unknown laws of growth and form. Others have argued that a biological
specialization for grammar is incompatible with every tenet of Darwinian theory
-- that it shows no genetic variation, could not exist in any intermediate
forms, confers no selective advantage, and would require more evolutionary time
and genomic space than is available. We examine these arguments and show that
they depend on inaccurate assumptions about biology or language or both.
Evolutionary theory offers clear criteria for when a trait should be attributed
to natural selection: complex design for some function, and the absence of
alternative processes capable of explaining such complexity. Human language meets this
criterion: grammar is a complex mechanism tailored to the transmission of
propositional structures through a serial interface. Autonomous and arbitrary
grammatical phenomena have been offered as counterexamples to the position that
language is an
adaptation, but this reasoning is unsound: communication protocols depend on
arbitrary conventions that are adaptive as long as they are shared.
Consequently, language
acquisition in the child should systematically differ from language evolution in the
species and attempts to analogize them are misleading. Reviewing other
arguments and data, we conclude that there is every reason to believe that a
specialization for grammar evolved by a conventional neo-Darwinian process.
Language
could not have begun in the form it was said to have taken in the first
recorded utterance of Thomas Babbington Macaulay (the infant Lord Macaulay):
once when he was taken out, his hostess accidently spilled hot tea on him. The
little lad first bawled his head off, but when he had calmed he said in answer
to his hostess' concern, "Thank you Madam, the agony is sensibly
abated." -- P. B. and J. S. Medawar
All human societies have language. As far as we know they always did; language was not invented by
some groups and spread to others like agriculture or the alphabet. All
languages are complex computational systems employing the same basic kinds of
rules and representations, with no notable correlation with technological
progress: the grammars of industrial societies are no more complex than the
grammars of hunter-gatherers; Modern English is not an advance over Old
English. Within societies, individual humans are proficient language users regardless of
intelligence, social status, or level of education. Children are fluent
speakers of complex grammatical sentences by the age of three, without benefit
of formal instruction. They are capable of inventing languages that are more
systematic than those they hear, showing resemblances to languages that they
have never heard, and they obey subtle grammatical principles for which there
is no evidence in their environments. Disease or injury can make people
linguistic savants while severely retarded, or linguistically impaired with
normal intelligence. Some language
disorders are genetically transmitted. Aspects of language skill can be linked to characteristic
regions of the human brain. The human vocal tract is tailored to the demands of
speech, compromising other functions such as breathing and swallowing. Human
auditory perception shows complementary specializations toward the demands of
decoding speech sounds into linguistic segments.
This list of facts (see Pinker, 1989a) suggests that
the ability to use a natural language
belongs more to the study of human biology than human culture; it is a topic
like echolocation in bats or stereopsis in monkeys, not like writing or the
wheel. All modern students of language
agree that at least some aspects of language are due to species-specific, task-specific
biological abilities, though of course there are radical disagreements about
specifics. A prominent position, outlined by Chomsky (1965, 1980, 1981, 1986,
1988a), Fodor (1983), Lenneberg (1964, 1967), and Liberman (Liberman, Cooper,
Shankweiler, & Studdert-Kennedy, 1967; Liberman and Mattingly, 1989), is
that the mind is composed of autonomous computational modules -- mental
faculties or "organs" -- and that the acquisition and representation
of language is the
product of several such specialized modules.
It would be natural, then, to
expect everyone to agree that human language is the product of Darwinian natural selection. The
only successful account of the origin of complex biological structure is the
theory of natural selection, the view that the differential reproductive
success associated with heritable variation is the primary organizing force in
the evolution of organisms (Darwin, 1859; see Bendall, 1983 for a contemporary
perspective). But surprisingly, this conclusion is contentious. Noam Chomsky,
the world's best-known linguist, and Stephen Jay Gould, the world's best-known
evolutionary theorist, have repeatedly suggested that language may not be the
product of natural selection, but a side effect of other evolutionary forces
such as an increase in overall brain size and constraints of as-yet unknown
laws of structure and growth (e.g., Chomsky, 1972, 1982a, 1982b, 1988a, 1988b;
Gould, 1987a; Gould and Piattelli-Palmarini, 1987). Recently Massimo
Piattelli-Palmarini (1989), a close correspondent with Gould and Chomsky, has
done the field a service by formulating a particularly strong version of their
positions and articulating it in print. Premack (1985, 1986) and Mehler (1985)
have expressed similar views.
In this paper we will examine this
position in detail, and will come to a very different conclusion. We will argue
that there is every reason to believe that language has been shaped by natural selection as
it is understood within the orthodox "synthetic" or
"neo-Darwinian" theory of evolution (Mayr, 1982). In one sense our
goal is incredibly boring. All we argue is that language is no different from other complex
abilities such as echolocation or stereopsis, and that the only way to explain
the origin of such abilities is through the theory of natural selection. One
might expect our conclusion to be accepted without much comment by all but the most
environmentalist of language
scientists (as indeed it is by such researchers as Bickerton, 1981, Liberman
and Mattingly, 1989, Lieberman, 1984, and, in limited respects, by Chomsky
himself in some strands of his writings.(Note 1)). On the other hand, when two
such important scholars as Chomsky and Gould repeatedly urge us to consider a
startling contrary position, their arguments can hardly be ignored. Indeed
these arguments have had a strong effect on many cognitive scientists, and the
nonselectionist view has become the consensus in many circles.
Furthermore, a lot is at stake if
our boring conclusion is wrong. We suspect that many biologists would be
surprised at the frequent suggestion that the complexity of language cannot be explained
through natural selection. For instance, Chomsky has made the following
statements:
[an innate language
faculty] poses a problem for the biologist, since, if true, it is an example of
true 'emergence' -- the appearance of a qualitatively different phenomenon at a
specific stage of complexity of organization. (1972: 70)
It is perfectly safe to attribute
this development [of innate mental structure] to "natural selection",
so long as we realize that there is no substance to this assertion, that it
amounts to nothing more than a belief that there is some naturalistic
explanation for these phenomena. (1972: 97)
Evolutionary theory is
informative about many things, but it has little to say, as of now, of
questions of this nature [e.g., the evolution of language]. The answers may well lie not so much
in the theory of natural selection as in molecular biology, in the study of
what kinds of physical systems can develop under the conditions of life on
earth and why, ultimately because of physical principles. (1988a: 167)
It does seem very hard to believe
that the specific character of organisms can be accounted for purely in terms
of random mutation and selectional controls. I would imagine that the biology
of a 100 years from now is going to deal with the evolution of organisms the
way it now deals with the evolution of amino acids, assuming that there is just
a fairly small space of physically possible systems that can realize
complicated structures. .. Evolutionary theory appears to have very little to
say about speciation, or about any kind of innovation. It can explain how you
get a different distribution of qualities that are already present, but it does
not say much about how new qualities can emerge. (1982a:23)
If findings coming out of the study of language forced biologists to
such conclusions, it would be big news.
There is another reason to
scrutinize the nonselectionist theory of language. If a current theory of language is truly
incompatible with the neo-Darwinian theory of evolution, one could hardly blame
someone for concluding that it is not the theory of evolution that must be
questioned, but the theory of language.
Indeed, this argument has been the basis of critiques of Chomsky's theories by
Bates, Thal, and Marchman (1989), Greenfield (1987), and Lieberman (1984,
1989), who are nonetheless strange bedfellows with Chomsky in doubting whether
an innate generative grammar could have evolved by natural selection. Since we
are impressed both by the synthetic theory of evolution and by the theory of
generative grammar, we hope that we will not have to choose between the two.
In this paper, we first examine
arguments from evolutionary biology about when it is appropriate to invoke
natural selection as an explanation for the evolution of some trait. We then
apply these tests to the case of human language, and conclude that language passes. We examine the motivations for
the competing nonselectionist position, and suggest that they have little to
recommend them. In the final section, we refute the arguments that have claimed
that an innate specialization for grammar is incompatible with the tenets of a
Darwinian account and thus that the two are incompatible.
Gould has frequently suggested that evolutionary theory is
in the throes of a scientific revolution (e.g., Eldredge & Gould, 1977;
Gould, 1980). Two cornerstones of the Darwinian synthesis, adaptationism and
gradualism, are, he argues, under challenge. Obviously if strict Darwinism is
false in general it should not be used to explain the origin of language.
In a classic paper, Gould and Lewontin (1979) warn against
"naive adaptationism," the inappropriate use of adaptive theorizing
to explain traits that have emerged for other reasons (see also Kitcher, 1983;
Lewontin, 1978). The argument is illustrated by an analogy with the mosaics on
the dome and spandrels of the San Marco basilica in Venice:
Spandrels -- the tapering triangular spaces formed by
the intersection of two rounded arches at right angles ... are necessary
architectural by-products of mounting a dome on rounded arches. Each spandrel
contains a design admirably fitted into its tapering space. An evangelist sits
in the upper part flanked by the heavenly cities. Below, a man representing one
of the four biblical rivers ... pours water from a pitcher in the narrowing
space below his feet.
The design is so elaborate,
harmonious, and purposeful that we are tempted to view it as the starting point
of any analysis, as the cause in some sense of the surrounding architecture.
But this would invert the proper path of analysis. The system begins with an
architectural constraint: the necessary four spandrels and their tapering
triangular form. They provide a space in which the mosaicists worked; they set
the quadripartite symmetry of the dome above.
Such architectural constraints
abound, and we find them easy to understand because we do not impose our
biological biases upon them. ... Anyone who tried to argue that the structure
[spandrels] exists because of [the designs laid upon them] would be inviting
the same ridicule that Voltaire heaped on Dr. Pangloss: "Things cannot be
other than they are ... Everything is made for the best purpose. Our noses were
made to carry spectacles, so we have spectacles. Legs were clearly intended for
breeches, and we wear them." ... Yet evolutionary biologists, in their
tendency to focus exclusively on immediate adaptation to local conditions, do
tend to ignore architectural constraints and perform just such an inversion of
explanation. (pp. 147-149)
Unconvincing adaptationist explanations, which Gould and
Lewontin compare to Kipling's "Just-so stories," are easy to find. In
the Science and Technology section of the Boston Globe in March 1987, an
article noted that the number of teats in different mammals ought to correspond
not to the average litter size but to the largest litter size that can occur
for that species within some bound of probability. Since humans ordinarily bear
single children but not infrequently have twins, we have an explanation for why
humans have two breasts, not one. The author did not discuss the possibility
that the bilateral symmetry that is so basic to the mammalian body plan makes
the appearance of one-breasted humans rather unlikely. Gould and Lewontin
describe a number of nonadaptationist mechanisms that they feel are frequently
not tested within evolutionary accounts: genetic drift, laws of growth and form
(such as general allometric relations between brain and body size), direct
induction of form by environmental forces such as water currents or gravity,
the effects of accidents of history (which may trap organisms in local maxima
in the adaptive landscape), and "exaptation" (Gould and Vrba, 1982),
whereby new uses are made of parts that were originally adapted to some other
function or of spandrels that had no function at all but were present for
reasons of architecture, development, or history. They point out that Darwin
himself had this pluralistic view of evolution, and that there was an
"unfairly maligned" nonadaptationist approach to evolution, prominent
in continental Europe, that stressed constraints on "Baupl@act[c]ne"
(architectural plans) flowing from phyletic history and embryological
development. This body of research, they suggest, is an antidote to the
tendency to treat an organism as a bundle of traits or parts, each
independently shaped by natural selection.
The Gould and Lewontin argument could be interpreted as
stressing that since the neo-Darwinian theory of evolution includes
nonadaptationist processes it is bad scientific practice not to test them as
alternatives to natural selection in any particular instance. However, they are
often read as having outlined a radical new alternative to Darwin, in which
natural selection is relegated to a minor role. Though Gould and Lewontin
clearly eschew this view in their paper, Gould has made such suggestions
subsequently (e.g., Gould, 1980), and Piattelli-Palmarini (1989: 1) has
interpreted it as such when he talks of Darwinian natural selection being
replaced by "a better evolutionary theory (one based on
'exaptation')". The reasons why we should reject this view were spelled
out clearly by Williams (1966), and have been amplified recently by Dawkins
(1983, 1986).
The key point that blunts the Gould
and Lewontin critique of adaptationism is that natural selection is the only
scientific explanation of adaptive complexity. "Adaptive complexity"
describes any system composed of many interacting parts where the details of
the parts' structure and arrangement suggest design to fulfill some function.
The vertebrate eye is the classic example. The eye has a transparent refracting
outer cover, a variable-focus lens, a light-sensitive layer of neural tissue
lying at the focal plane of the lens, a diaphragm whose diameter changes with
illumination level, muscles that move it in precise conjunction and convergence
with those of the other eye, and elaborate neural circuits that respond to
patterns defining edges, colors, motion, and stereoscopic disparity. It is
impossible to make sense of the structure of the eye without noting that it
appears as if it was designed for the purpose of seeing -- if for no other
reason that the man-made tool for image formation, the camera, displays an
uncanny resemblance to the eye. Before Darwin, theologians, notably William
Paley, pointed to its exquisite design as evidence for the existence of a
divine designer. Darwin showed how such "organs of extreme perfection and
complication" could arise from the purely physical process of natural
selection.
The essential point is that no
physical process other than natural selection can explain the evolution of an
organ like the eye. The reason for this is that structures that can do what the
eye does are extremely low-probability arrangements of matter. By an
unimaginably large margin, most objects defined by the space of biologically possible
arrangements of matter cannot bring an image into focus, modulate the amount of
incoming light, respond to the presence of edges and depth boundaries, and so
on. The odds that genetic drift, say, would result in the fixation within a
population of just those genes that would give rise to such an object are
infinitesimally small, and such an event would be virtually a miracle. This is
also true of the other nonselectionist mechanisms outlined by Gould and
Lewontin. It is absurdly improbable that some general law of growth and form
could give rise to a functioning vertebrate eye as a by-product of some other
trend such as an increase in size of some other part. Likewise, one need not
consider the possibility that some organ that arose as an adaptation to some
other task, or a spandrel defined by other body parts, just happened to have a
transparent lens surrounded by a movable diaphragm in front of a
light-sensitive layer of tissue lying at its focal plane. Natural selection --
the retention across generations of whatever small, random modifications yield
improvements in vision that increase chances of survival and reproduction -- is
the only physical process capable of creating a functioning eye, because it is
the only physical process in which the criterion of being good at seeing can
play a causal role. As such it is the only process that can lead organisms
along the path in the astronomically vast space of possible bodies leading from
a body with no eye to a body with a functioning eye.
This argument is obviously
incomplete, as it relies on the somewhat intuitive notion of
"function" and "design." A skeptic might accuse the
proponent of circularity, asking why a lump of clay should not be considered
well-designed to fulfill the function of taking up exactly the region of space
that it in fact takes up. But the circle can be broken in at least three ways.
First, biologists need posit far fewer functions than there are biological
systems; new functions are not invented for each organ of each organism. Furthermore,
each legitimate function can be related via a direct plausible causal chain to
other functions and -- critically -- to the overall function of survival and
reproduction. Finally, convergent evolution and resemblance to human artifacts
fulfilling the same putative function give independent criteria for design. But
regardless of the precise formulation of the modern argument from design (see,
e.g., Cummins, 1984), it is not controversial in practice. Gould himself
readily admits that natural selection is the cause of structures such as the
vertebrate eye, and he invokes the criterion of engineering design, for
example, to rescue Darwinism itself from the charge of circularity (Gould,
1977a). Presumably this is why Gould and Lewontin concede that they agree with
Darwin that natural selection is "the most important of evolutionary
mechanisms."
What, then, is the proper relation
between selectionist and nonselectionist explanations in evolution? The least
interesting case involves spandrels that are not involved in any function or
behavior, such as the redness of blood, the V-shaped space between a pair of
fingers, the hollow at the back of a knee, the fact there are a prime number of
digits on each limb, and so on. The mere presence of these epiphenomenal
spandrels, that play no direct role in the explanation of any species-typical
behavior or function, says nothing about whether the structures that they are
associated with were shaped by selection. There are as many of them as there
are ways of describing an organism that do not correspond to its functional
parts.
Much more important are cases where
spandrels are modified and put to use. However, in such cases of modified
spandrels, selection plays a crucial role. Putting a dome on top of four arches
gives you a spandrel, but it does not give you a mosaic depicting an evangelist
and a man pouring water out of a pitcher. That would really be a miracle. To
get the actual mosaic you need a designer. The designer corresponds to natural
selection. Spandrels, exaptations, laws of growth, and so on can explain the
basic plans, parts, and materials that natural selection works with -- as Jacob
(1977) put it, nature is a tinkerer, not an engineer with a clean drawing
board. The best examples of structures produced entirely by nonadaptationist
mechanisms are generally one-part or repetitive shapes or processes that
correspond to simple physical or geometric laws, such as chins, hexagonal
honeycombs, large heads on large bodies, and spiral markings. But, as Darwin stressed,
when such parts and patterns are modified and combined into complex biological
machines fulfilling some delicate function, these subsequent modifications and
arrangements must be explained by natural selection.
The real case of evolution without
selection consists of the use of unmodified spandrels. Gould (1987a) describes
a kind of wading bird that uses its wings primarily to block reflections on the
surface of water while looking for fish. The possibility that some useful
structure is an unmodified spandrel is the most interesting implication of the
Gould-Lewontin argument, since Darwinian natural selection would really play no
role. Note, though, that unmodified spandrels have severe limitations. A wing
used as a visor is a case where a structure designed for a complex engineering
task that most arrangements of matter do not fulfill, such as controlled
flight, is exapted to a simple engineering task that many arrangements of
matter do fulfill, such as screening out reflections (we are reminded of the
paperweight and aquarium depicted in 101 Uses for a Dead Computer.) When the
reverse happens, such as when a solar heat exchanger is retooled as a fully
functioning wing in the evolution of insects (Kingsolver and Koehl, 1985),
natural selection must be the cause.
We are going over these criteria
for invoking natural selection in such detail because they are so often
misunderstood. We hope we have made it clear why modern evolutionary biology
does not license Piattelli-Palmarini's conclusion that "since language and cognition
probably represent the most salient and the most novel biological traits of our
species, ... it is now important to show that they may well have arisen from
totally extra-adaptive mechanisms." And Piattelli-Palmarini is not alone. In
many discussions with cognitive scientists we have found that adaptation and
natural selection have become dirty words. Anyone invoking them is accused of
being a a naive adaptationist, or even of "misunderstanding
evolution." Worst of all, he or she is open to easy ridicule as a Dr.
Pangloss telling Just-so stories! (Premack's 1986 reply to Bickerton, 1986, is
typical.) Given the uncontroversially central role of natural selection in
evolution, this state of affairs is unfortunate. We suspect that many people
have acquired much of their knowledge of evolutionary theory from Gould's
deservedly popular essays. These essays present a view of evolution that is
vastly more sophisticated than the 19th-Century versions of Darwin commonly
taught in high schools and even colleges. But Gould can easily be misread as
fomenting a revolution rather than urging greater balance within current
biological research, and his essays do not emphasize the standard arguments for
when it is appropriate, indeed necessary, to invoke natural selection.
Also lurking beneath people's
suspicions of natural selection is a set of methodological worries. Isn't
adaptationism fundamentally untestable, hence unscientific, because adaptive
stories are so easy to come by that when one fails, another can always be
substituted? Gould and Lewontin may be correct in saying that biologists and
psychologists have leapt too quickly to unmotivated and implausible
adaptationist explanations, but this has nothing to do with the logic of
adaptationist explanations per se. Glib, unmotivated proposals can come from
all kinds of theories. To take an example close to home, the study of the
evolution of language
attained its poor reputation precisely because of the large number of silly
nonadaptationist hypotheses that were proposed. For instance, it has been
argued that language
arose from mimicry of animal calls, imitations of physical sounds, or grunts of
exertion (the infamous "bow-wow," "ding-dong," and
"heave-ho" theories.)
Specific adaptationist proposals
are testable in principle and in practice (see Dennett, 1983; Kitcher, 1983;
Maynard Smith, 1984, Mayr, 1982; Sober, 1984; Williams, 1966.) Supplementing
the criterion of complex design, one can determine whether putatively adaptive
structures are correlated with the ecological conditions that make them useful,
and under certain circumstance one can actually measure the reproductive
success of individuals possessing them to various degrees (see, e.g.,
Clutton-Brock, 1983). Of course, the entire theory of natural selection may be
literally unfalsifiable in the uninteresting sense that elaborations can always
rescue its empirical failings, but this is true of all large-scale scientific
theories. Any such theory is supported to the extent that the individual
elaborations are mutually consistent, motivated by independent data, and few in
number compared to the phenomena to be explained.(Note 2)
Indeed one could argue that it is
nonadaptationist accounts that are often in grave danger of vacuity. Specific
adaptationist proposals may be unmotivated, but they are within the realm of
biological and physical understanding, and often the problem is simply that we
lack the evidence to determine which account within a set of alternative
adaptive explanations is the correct one. Nonadaptationist accounts that merely
suggest the possibility that there is some hitherto-unknown law of physics or
constraint on form -- a "law of eye-formation," to take a caricatured
example -- are, in contrast, empty and nonfalsifiable.
There are two other issues that Gould includes in his
depiction of a scientific revolution in evolutionary theory. It is important to
see that they are largely independent of the role of selection in evolutionary
change.
According to the theory of "punctuated
equilibrium" (Eldredge and Gould, 1972; Gould and Eldredge, 1977), most
evolutionary change does not occur continuously within a lineage, but is
confined to bursts of change that are relatively brief on the geological time
scale, generally corresponding to speciation events, followed by long periods
of stasis. Gould has suggested that the theory has some very general and crude
parallels with approaches to evolution that were made disreputable by the
neo-Darwinian synthesis, approaches that go by the names of
"saltationism," "macromutations," or "hopeful
monsters." (e.g., Gould, 1981). However, he is emphatic that punctuated
equilibrium is "a theory about ordinary speciation (taking tens of
thousands of years) and its abrupt appearance at low scales of geological
resolution, not about ecological catastrophe and sudden genetic change"
(Gould, 1987b: 234). Many other biologists see evolutionary change in an even
more orthodox light. They attribute the sudden appearance of fully-formed new
kinds of organisms in the fossil record to the fact that speciation typically
takes place in small, geographically isolated populations. Thus transitional
forms, even if evolving over very long time-spans, are unlikely to appear in
the fossil record until they reinvade the ancestral territory; it is only the
invasion that is sudden (see, e.g., Ayala, 1983; Dawkins, 1986; Mayr, 1982;
Stebbins and Ayala, 1981). In any case it is clear that evolutionary change is
gradual from generation to generation, in full agreement with Darwin. Thus
Piattelli-Palmarini (1989: 8) expresses a common misunderstanding when he
interprets the theory of punctuated equilibrium as showing that "many
incomplete series in the fossil record are incomplete, not because the
intermediate forms have been lost for us, but because they simply never
existed".
Once again the explanation of
adaptive complexity is the key reason why one should reject nongradual change
as playing an important role within evolution. An important Darwinian insight,
reinforced by Fisher (1930), is that the only way for complex design to evolve
is through a sequence of mutations with small effects. Although it may not
literally be impossible for an organ like the eye to emerge across one
generation from no eye at all, the odds of this happening are unimaginably low.
A random large leap in the space of possible organic forms is astronomically
unlikely to land an organism in a region with a fully formed functioning eye.
Only a hill-climbing process, with each small step forced in the direction of
forms with better vision, can guide the lineage to such a minuscule region of
the space of possible forms within the lifetime of the universe.
None of this is to deny that
embryological processes can result in quite radical single-generation
morphological changes. "Homeotic" mutations causing slight changes in
the timing or positioning of epigenetic processes can result in radically new
kinds of offspring, such as fruit flies with legs growing where their antenna
should be, and it is possible that some speciation events may have begun with
such large changes in structure. However there is a clear sense in which such
changes are still gradual, since they only involve a gross modification or
duplication of existing structure, not the appearance of a new kind of
structure (see Dawkins, 1983).
Exaptation is another process that is sometimes discussed as
if it was incompatible both with adaptationism and with gradualism. People
often wonder whether each of the "numerous, successive, slight
modifications" from an ancestor lacking an organ to a modern creature
enjoying the fully-functioning organ leads to an improvement in the function,
as it should if the necessary evolutionary sequence is to be complete.
Piattelli-Palmarini cites Kingsolver and Koehl's (1985) study of qualitative
shifts during the evolution of wings in insects, which are ineffective for
flight below a certain size, but effective as solar heat exchange panels
precisely within that range. (The homologies among parts of bat wings, seal
flippers, horse forelimbs, and human arms is a far older example). Nevertheless
such exaptations are still gradual and are still driven by selection; there
must be an intermediate evolutionary stage at which the part can subserve both
functions (Mayr, 1982), after which the process of natural selection shapes it
specifically for its current function. Indeed the very concept of exaptation is
essentially similar to what Darwin called "preadaptation," and played
an important role in his explanation of "the incipient stages of useful
structures."
Furthermore, it is crucial to
understand that exaptation is merely one empirical possibility, not a universal
law of evolution. Gould is often quoted as saying "We avoid the excellent
question, What good is 5 percent of an eye? by arguing that the possessor of
such an incipient structure did not use it for sight."(1977b:107). (Of
course no ancestor to humans literally had 5 percent of a human eye; the
expression refers to an eye that has 5 percent of the complexity of a modern
eye). In response, Dawkins (1986: 81) writes: "An ancient animal with 5
per cent of an eye might indeed have used it for something other than sight,
but it seems to me at least as likely that it used it for 5 per cent vision.
... Vision that is 5 percent as good as yours or mine is very much worth having
in comparison with no vision at all. So is 1 per cent vision better than total blindness.
And 6 per cent is better than 5, 7 per cent better than 6, and so on up the
gradual, continuous series." Indeed Darwin (1859) sketched out a
hypothetical sequence of intermediate forms in the evolution of the vertebrate
eye, all with counterparts in living organisms, each used for vision.
In sum, the positions of Gould,
Lewontin, and Eldredge should not be seen as radical revisions of the theory of
evolution, but as a shift in emphasis within the orthodox neo-Darwinian
framework. As such they do not invalidate gradual natural selection as the
driving force behind the evolution of language on a priori grounds. Furthermore, there are clear
criteria for when selectionist and nonselectionist accounts should be invoked
to explain some biological structure: complex design to carry out some
reproductively significant function, versus the existence of a specific
physical, developmental or random process capable of explaining the structure's
existence. With these criteria in hand, we can turn to the specific problem at
hand, the evolution of language.
Do the cognitive mechanisms underlying language show signs of design
for some function in the same way that the anatomical structures of the eye
show signs of design for the purpose of vision? This breaks down into three
smaller questions: What is the function (if any) of language? What are the engineering demands on a
system that must carry out such a function? And are the mechanisms of language tailored to meet
those demands? We will suggest that language show signs of design for the communication of
propositional structures over a serial channel.
Humans acquire a great deal of information during their
lifetimes. Since this acquisition process occurs at a rate far exceeding that
of biological evolution, it is invaluable in dealing with causal contingencies
of the environment that change within a lifetime, and provides a decisive
advantage in competition with other species that can only defend themselves
against new threats in evolutionary time (Brandon and Hornstein, 1986; Tooby
and deVore, 1987). There is an obvious advantage in being able to acquire such
information about the world second-hand: by tapping into the vast reservoir of
knowledge accumulated by some other individual, one can avoid having to
duplicate the possibly time-consuming and dangerous trial and error process
that won that knowledge. Furthermore, within a group of interdependent,
cooperating individuals, the states of other individuals are among the most
significant things in the world worth knowing about. Thus communication of
knowledge and internal states is useful to creatures who have a lot to say and
who are on speaking terms. (In Section MASTODONS, we discuss evidence that our
ancestors were such creatures.)
Human knowledge and reasoning, it
has been argued, is couched in a "language of thought" that is distinct from external
languages such as English or Japanese (Fodor, 1975). The propositions in this
representational medium are relational structures whose symbols pertain to
people, objects, and events, the categories they belong to, their distribution
in space and time, and their causal relations to one another (Jackendoff, 1983;
Keil, 1979). The causal relations governing the behavior of other people are
understood as involving their beliefs and desires, which can be considered as
relations between an individual and the proposition that represents the content
of that belief or desire (Fodor, 1985, 1987).
This makes the following kinds of
contents as worthy of communication among humans. We would want to be able to
refer to individuals and classes, to distinguish among basic ontological
categories (things, events, places, times, manners, and so on), to talk about
events and states, distinguishing the participants in the event or state
according to role (agents, patients, goals), and to talk about the intentional
states of ourselves and others. Also, we would want the ability to express
distinctions of truth value, modality (necessity, possibility, probability,
factivity), to comment on the time of an event or state including both its
distribution over time (continuous, iterative, punctate) and its overall time
of occurrence. One might also demand the ability to encode an unlimited number
of predicates, arguments, and propositions. Further, it would be useful to be
able to use the same propositional content within different speech acts; for
instance, as a question, a statement, or a command. Superimposed on all of this
we might ask for an ability to focus or to put into the background different
parts of a proposition, so as to tie the speech act into its context of
previously conveyed information and patterns of knowledge of the listener.
The vocal-auditory channel has some
desirable features as a medium of communication: it has a high bandwidth, its
intensity can be modulated to conceal the speaker or to cover large distances,
and it does not require light, proximity, a face-to-face orientation, or tying
up the hands. However it is essentially a serial interface, lacking the full
two-dimensionality needed to convey graph or tree structures and typographical
devices such as fonts, subscripts, and brackets. The basic tools of a coding
scheme employing it are an inventory of distinguishable symbols and their
concatenation.
Thus grammars for spoken languages
must map propositional structures onto a serial channel, minimizing ambiguity
in context, under the further constraints that the encoding and decoding be
done rapidly, by creatures with limited short-term memories, according to a
code that is shared by an entire community of potential communicants.
The fact that language is a complex system
of many parts, each tailored to mapping a characteristic kind of semantic or
pragmatic function onto a characteristic kind of symbol sequence, is so obvious
in linguistic practice that it is usually not seen as worth mentioning. Let us
list some uncontroversial facts about substantive universals, the building
blocks of grammars that all theories of universal grammar posit, either as an
explicit inventory or as a consequence of somewhat more abstract mechanisms.
-Grammars are built around symbols
for major lexical categories (noun, verb, adjective, preposition) that can
enter into rules specifying telltale surface distributions (e.g., verbs but not
nouns generally take unmarked direct objects), inflections, and lists of
lexical items. Together with minor categories that characteristically co-occur
with the major ones (e.g., articles with nouns), the different categories are
thus provided with the means of being distinguished in the speech string. These
distinctions are exploited to distinguish basic ontological categories such as
things, events or states, and qualities. (See, e.g., Jackendoff, 1983, 1988.)
-Major phrasal categories (noun
phrase, verb phrase, etc.) start off with a major lexical item, the
"head," and allow it to be combined with specific kinds of affixes
and phrases. The resulting conglomerate is then used to refer to entities in our
mental models of the world. Thus a noun like dog does not itself describe
anything but it can combine with articles and other parts of speech to make
noun phrases, such as those dogs, my dog, and the dog that bit me, and it is
these noun phrases that are used to describe things. Similarly, a verb like hit
is made into a verb phrase by marking it for tense and aspect and adding an
object, thus enabling it to describe an event. In general, words encode
abstract general categories and only by contributing to the structure of major
phrasal categories can they describe particular things, events, states,
locations, and properties. This mechanism enables the language-user to refer to an
unlimited range of specific entities while possessing only a finite number of
lexical items (See, e.g., Bloom, 1989; Jackendoff, 1977).
-Phrase structure rules (e.g.,
"X-bar theory" or "immediate dominance rules") force
concatenation in the string to correspond to semantic connectedness in the
underlying proposition, and thus provides linear clues of underlying structure,
distinguishing, for example, Large trees grow dark berries from Dark trees grow
large berries. (See, e.g., Gazdar, Pullum, Klein, and Sag, 1985; Jackendoff,
1977).
-Rules of linear order (e.g.,
"directional parameters" for ordering heads, complements, and
specifiers, or "linear precedence rules") allow the order of words
within these concatenations to distinguish among the argument positions that an
entity assumes with respect to a predicate, distinguishing Man bites dog from
Dog bites man. (See, e.g., Gazdar, et al., 1985; Travis, 1984.)
-Case affixes on nouns and
adjectives can take over these functions, marking nouns according to argument
role and linking noun with predicate even when the order is scrambled. This
redundancy can free up the device of linear order, allowing it to be exploited
to convey relations of prominence and focus, which can thus mesh with the
necessarily temporal flow of attention and knowledge acquisition in the
listener.
-Verb affixes signal the temporal
distribution of the event that the verb refers to (aspect) and the time of the
event (tense); when separate aspect and tense affixes co-occur, they are in a
universally preferred order (aspect closer to the verb; Bybee, 1985). Given
that man-made timekeeping devices play no role in species-typical human
thought, some other kind of temporal coordinates must be used, and languages
employ an ingenious system that can convey the time of an event relative to the
time of the speech act itself and relative to a third, arbitrary reference time
(thus we can distinguish between John has arrived, John had arrived (when Mary
was speaking), John will have arrived (before Mary speaks), and so on;
Reichenbach, 1947). Verb affixes also typically agree with the subject and
other arguments, and thus provide another redundant mechanism that can convey
predicate-argument relations by itself (e.g., in many Native American languages
such as Cherokee and Navajo) or that can eliminate ambiguity left open by other
mechanisms (distinguishing, e.g., I know the boy and the girl who like
chocolate from I know the boy and the girl who likes chocolate).
-Auxiliaries, which occur either as
verb affixes (where they are distinguished from tense and aspect affixes by
proximity to the verb) or in one of three sentence-peripheral positions (first,
second, last), convey relations that have logical scope over the entire
proposition (mirroring their peripheral position) such as truth value,
modality, and illocutionary force. (See Steele, Akmajian, Demers, Jelinek,
Kitagawa, Oehrle, & Wasow, 1981).
-Languages also typically contain a
small inventory of phonetically reducible morphemes -- pronouns and other
anaphoric elements -- that by virtue of encoding a small set of semantic features
such as gender and humanness, and being restricted in their distribution, can
convey patterns of coreference among different participants in complex
relations without the necessity of repeating lengthy definite descriptions
(e.g., as in A boy showed a dog to a girl and then he/she/it touched
him/her/it/himself/herself). (See Chomsky, 1981; Wexler and Manzini, 1984).
-Mechanisms of complementation and
control govern the expression of propositions that are arguments of other
propositions, employing specific complementizer morphemes signaling the
periphery of the embedded proposition and indicating its relation to the
embedding one, and licensing the omission of repeated phrases referring to
participants playing certain combinations of roles. This allows the expression
of a rich set of propositional attitudes within a belief-desire folk
psychology, such as John tried to come, John thinks that Bill will come, John
hopes for Bill to come, John convinced Bill to come, and so on. (See Bresnan,
1982).
-In wh-movement (as in wh-questions
and relative clauses) there is a tightly constrained cooccurrence pattern
between an empty element (a "trace" or "gap") and a
sentence-peripheral quantifier (e.g., wh-words). The quantifier-word can be
specific as to illocutionary force (question versus modification), ontological
type (time, place, purpose), feature (animate/inanimate), and role
(subject/object), and the gap can occur only in highly constrained phrase
structure configurations. The semantics of such constructions allow the speaker
to fix the reference of, or request information about, an entity by specifying
its role within any proposition. One can refer not just to any dog but to the
dog that Mary sold __ to some students last year; one can ask not only for the
names of just any old interesting person but specifically Who was that woman I
saw you with __? (See, e.g., Chomsky, 1981; Gazdar, Pullum, Klein, and Sag,
1985; Kaplan and Bresnan, 1982).
And this is only a partial list,
focusing on sheer expressive power. One could add to it the many syntactic
constraints and devices whose structure enables them to minimize memory load
and the likelihood of pursuing local garden paths in speech comprehension
(e.g., Berwick and Weinberg, 1984; Berwick and Wexler, 1987; Bever, 1970;
Chomsky and Lasnik, 1977; Frazier, Clifton, and Randall, 1983; Hawkins and
Cutler, 1988; Kuno, 1973, 1974), or to ease the task of analysis for the child
learning the language
(e.g., Morgan, 1986; Pinker,
1984; Wexler and Culicover, 1980). On top of that there are the rules of
segmental phonology that smooth out arbitrary concatenations of morphemes into
a consistent sound pattern that juggles demands of ease of articulation and
perceptual distinctness; the prosodic rules that disambiguate syntax and
communicate pragmatic and illocutionary information; the articulatory programs
that achieve rapid transmission rates through parallel encoding of adjacent
consonants and vowels; and on and on. Language seems to be a fine example of "that
perfection of structure and coadaptation which justly excites our
admiration" (Darwin, 1859: 26).
As we write these words, we can
hear the protests: "Pangloss! Just-so stories!" Haven't we just
thought up accounts about functions post hoc after examining the structure? How
do we know that the neural mechanisms were not there for other reasons, and
that once they were there they were just put to various convenient uses by the
first language
users, who then conveyed their invention to subsequent generations?
First of all, there is nothing particularly ingenious,
contorted, or exotic about our claims for substantive universals and their
semantic functions. Any one of them could have been lifted out of the pages of
linguistics textbooks. It is hardly the theory of evolution that motivates the
suggestion that phrase structure rules are useful in conveying relations of
modification and predicate-argument structure.
Second, it is not necessarily
illegitimate to infer both special design and adaptationist origins on the
basis of function itself. It all depends on the complexity of the function from
an engineering point of view. If someone told you that John uses X as a
sunshade or a paperweight, you would certainly be hard-pressed to guess what X
is or where X came from, because all sorts of things make good sunshades or
paperweights. But if someone told you that John uses X to display television
broadcasts, it would be a very good bet that X is a television set or is
similar in structure to one, and that it was designed for that purpose. The
reason is that it would be vanishingly unlikely for something that was not
designed as a television set to display television programs; the engineering
demands are simply too complex.
This kind of reasoning is commonly
applied in biology when high-tech abilities such as bat sonar are discovered.
We suggest that human language
is a similar case. We are not talking about noses holding up spectacles. Human language is a device capable
of communicating exquisitely complex and subtle messages, from convoluted soap
opera plots to theories of the origin of the universe. Even if all we knew was
that humans possessed such a device, we would expect that it would have to have
rather special and unusual properties suited to the task of mapping complex
propositional structures onto a serial channel, and an examination of grammar
confirms this expectation.
Third, arguments that language is designed for
communication of propositional structures are far from logical truths. It is
easy to formulate, and reject, specific alternatives. For example, occasionally
it is suggested that language
evolved as a medium of internal knowledge representation for use in the
computations underlying reasoning. But while there may be a language-like
representational medium -- "the language of thought," or "mentalese" (Fodor,
1975) -- it clearly cannot be English, Japanese, and so on. Natural languages
are hopeless for this function: they are needlessly serial, rife with ambiguity
(usually harmless in conversational contexts, but unsuited for long term
knowledge representation), complicated by alternations that are relevant only
to discourse (e.g., topicalization), and cluttered with devices (such as
phonology and much of morphology) that make no contribution to reasoning.
Similarly, the facts of grammar make it difficult to argue that language shows design for
"the expression of thought" in any sense that is substantially
distinct from "communication." If "expression" refers to
the mere externalization of thoughts, in some kind of monologue or soliloquy,
it is an unexplained fact that language
contains mechanisms that presuppose the existence of a listener, such as rules
of phonology and phonetics (which map sentences onto sound patterns, enhance
confusable phonetic distinctions, disambiguate phrase structure with
intonation, and so on.) and pragmatic devices that encode conversational topic,
illocutionary force, discourse antecedents, and so on. Furthermore people do
not express their thoughts in an arbitrary private language (which would be sufficient for pure
"expression"), but have complex learning mechanisms that acquire a language highly similar in
almost every detail to those of other speakers in the community.
Another example of of the empirical
nature of specific arguments for language
design appears when we examine the specific expressive abilities that are
designed into language.
They turn out to constitute a well-defined set, and do not simply correspond to
every kind of information that humans are interested in communicating. So
although we may have some a priori intuitions regarding useful expressive
capacities of grammar, the matter is ultimately empirical (see, e.g.,
Jackendoff, 1983, 1990; Pinker,
1989b; Talmy, 1983, 1988), and such research yields results that are specific
enough to show that not just any intuition is satisfied. Grammar is a
notoriously poor medium for conveying subtle patterns of emotion, for example,
and facial expressions and tones of voice are more informative (Ekman and
Friesen, 1975; Etcoff, 1986). Although grammars provide devices for conveying
rough topological information such as connectivity, contact, and containment,
and coarse metric contrasts such as near/far or flat/globular, they are of very
little help in conveying precise Euclidean relations: a picture is worth a
thousand words. Furthermore, human grammar clearly lacks devices specifically
dedicated to expressing any of the kinds of messages that characterize the
vocal communication systems of cetaceans, birds, or nonhuman primates, such as
announcements of individual identity, predator warnings, and claims of
territory.
Finally, Williams (1966) suggests
that convergent evolution, resemblance to man-made artifacts, and direct
assessments of engineering efficiency are good sources of evidence for
adaptation. Of course in the case of human language these tests are difficult in practice:
significant convergent evolution has not occurred, no one has ever invented a
system that duplicates its function (except for systems that are obviously
parasitic on natural languages such as Esperanto or signed English), and most
forms of experimental intervention would be unethical. Nonetheless, some tests
are possible in principle, and this is enough to refute reflexive accusations
of circularity.
For example, even the artificial
languages that are focussed on very narrow domains of content and that are not
meant to be used in a natural on-line manner by people, such as computer
languages or symbolic logic, show certain obvious parallels with aspects of
human grammar. They have needed means of distinguishing types of symbols,
predicate argument relations, embedding, scope, quantification, and truth
relations, and solve these problems with formal syntactic systems that specify
arbitrary patterns of hierarchical concatenation, relative linear order, fixed
positions within strings, and closed classes of privileged symbols. Of course there
are vast dissimilarities but the mere fact that terms like "language,"
"syntax," "predicate," "argument," and
"statement" have clear meanings when applied to artificial systems,
with no confusion or qualification, suggests that there are nonaccidental
parallels that are reminiscent of the talk of diaphragms and lenses when
applied to cameras and eyes. As for experimental investigation, in principle
one could define sets of artificial grammars with and without one of the
mechanisms in question, or with variations of it. The grammars would be
provided or taught to pairs of communicators -- formal automata, computer
simulations, or college sophomores acting in conscious problem-solving mode --
who would be required to convey specific messages under different conditions of
speed, noise, or memory limitations. The proportion of information successfully
communicated would be assessed and examined as a function of the presence and
version of the grammatical mechanism, and of the different conditions putatively
relevant to the function in question.
A more serious challenge to the claim that grammars show
evidence of good design may come from the diversity of human languages
(Maratsos, 1989). Grammatical devices and expressive functions do not pair up
in one-to-one fashion. For example, some languages use word order to convey who
did what to whom; others use case or agreement for this purpose and reserve the
use of word order to distinguish topic from comment, or do not systematically
exploit word order at all. How can one say that the mental devices governing
word order evolved under selection pressure for expressing grammatical
relations if many languages do not use them for that purpose? Linguistic
diversity would seem to imply that grammatical devices are very general-purpose
tools. And a general-purpose tool would surely have a very generalized
structure, and thus could be a spandrel rather than an adapted machine. We
begin by answering the immediate objection that the existence of diversity, for
whatever reason, invalidates arguments for universal language design; at the end of the section
we offer some speculations as to why there should be more than one language to begin with.
First of all, the evolution of
structures that serve not one but a small number of definite functions, perhaps
to different extents in different environments, is common in biology (Mayr,
1982). Indeed, though grammatical devices are put to different uses in
different languages, the possible pairings are very circumscribed. No language uses noun affixes to
express tense or elements with the syntactic privileges of auxiliaries to
express the shape of the direct object. Such universal constraints on structure
and function are abundantly documented in surveys of the languages of the world
(e.g., Bybee, 1985; Comrie, 1981; Greenberg, 1966; Greenberg, Ferguson, and
Moravcsik, 1978; Hawkins, 1988; Keenan, 1987; and Shopen, 1985). Moreover language universals are
visible in language
history, where changes tend to fall into a restricted set of patterns, many
involving the introduction of grammatical devices obeying characteristic
constraints (Kiparsky, 1976; Wang, 1976).(Note 3)
But accounting for the evolution of
a language faculty
permitting restricted variation is only important on the most pessimistic of
views. Even a smidgin of grammatical analysis reveals that surface diversity is
often a manifestation of minor differences in the underlying mental grammars.
Consider some of the supposedly radical typological differences between English
and other languages. English is a rigid word-order language; in the Australian language Warlpiri the words
from different logical units can be thoroughly scrambled and case markers are
used to convey grammatical relations and noun modification. Many Native
American languages, such as Cherokee, use few noun phrases within clauses at
all, and express grammatical relations by sticking strings of agreement affixes
onto the verb, each identifying an argument by a set of features such as
humanness or shape. Whereas "accusative" languages like English
collapse subjects of transitive and intransitive sentences,
"ergative" languages collapse objects of transitives with subjects of
intransitives. Whereas English sentences are built around obligatory subjects,
languages like Chinese are oriented around a position reserved for the
discourse topic.
However, these variations almost
certainly correspond to differences in the extent to which the same specific
set of mental devices is put to use, but not to differences in the kinds of
devices that are put to use. English has free constituent order in strings of
prepositional phrases (The package was sent from Chicago to Boston by Mary; The
package was sent by Mary to Boston from Chicago, and so on). English has case,
both in pronouns and in the genitive marker spelled 's. It expresses
information about arguments in verb affixes in the agreement marker -s.
Ergativity can be seen in verb alternations like John broke the glass and The
glass broke. There is even a kind of topic position: As for fish, I like
salmon. Conversely, Warlpiri is not without phrasal syntax. Auxiliaries go in
second position (not unlike English, German, and many other languages). The
constituents of a noun phrase must be contiguous if they are not case-marked;
the constituents of a finite clause must be contiguous if the sentence contains
more than one. Pinker
(1984) outlines a theory of language
acquisition in which the same innate learning mechanisms are put to use to
different extents in children acquiring "radically" different
languages.
When one looks at more abstract
linguistic analyses, the underlying unity of natural languages is even more
apparent. Chomsky has quipped that anything you find in one language can also be found in
every other language,
perhaps at a more abstract level of representation, and this claim can be
justified without resorting to Procrustean measures. In many versions of his
Government-Binding theory (1981), all noun phrases must be case marked; even
those that receive no overt case-marking are assigned "abstract" case
by an adjacent verb, preposition, or tense element. The basic order of major
phrases is determined by the value of a language-varying parameter specifying the direction in which
case assignment may be executed. So in a language like Latin, the noun phrases are marked
with morphological case (and can appear in any position), while in a language like English, they
are not so marked, and must be adjacent to a case-assigner such as a verb. Thus
overt case marking in one language
and word order in another are unified as manifestations of a single grammatical
module. And the module has a well-specified function: in the terminology of the
theory, it makes noun phrases "visible" for the assignment of
thematic roles such as agent, goal, or location. Moreover, word order itself is
not a unified phenomenon. Often when languages "use word order for
pragmatic purposes," they are exploiting an underlying grammatical
subsystem, such as stylistic rules, that has very different properties from
that governing the relative order of noun phrases and their case-assigners.
Why is there more than one language at all? Here we can
only offer the most tentative of speculations. For sound-meaning pairings within
the lexicon, there are two considerations. First, one might suppose that
speakers need a learning mechanism for labels for cultural innovations, such as
screwdriver. Such a learning device is then sufficient for all vocabulary
items. Second, it may be difficult to evolve a huge innate code. Each of tens
of thousands of sound-meaning correspondences would have to be synchronized
across speakers, but few words could have the nonarbitrary antecedents that
would have been needed to get the standardization process started (i.e.,
analogous to the way bared fangs in preparation for biting evolved into the
facial expression for anger.) Furthermore the size of such a code would tax the
time available to evolve and maintain it in the genome in the face of random
perturbations from sexual recombination and other stochastic genetic processes
(Williams, 1966; Tooby and Cosmides, 1989). Once a mechanism for learning
sound-meaning pairs is in place, the information for acquiring any particular
pair, such as dog for dogs, is readily available from the speech of the
community. Thus the genome can store the vocabulary in the environment, as
Tooby and Cosmides (1989) have put it.
For other aspects of grammar, one
might get more insight by inverting the perspective. Instead of positing that
there are multiple languages, leading to the evolution of a mechanism to learn
the differences among them, one might posit that there is a learning mechanism,
leading to the development of multiple languages. That is, some aspects of grammar
might be easily learnable from environmental inputs by cognitive processes that
may have been in existence prior to the evolution of grammar, for example, the
relative order of a pair of sequenced elements within a bounded unit. For these
aspects there was no need to evolve a fixed value, and they are free to vary
across communities of speakers. In Section SHARED we discuss a simulation of
evolution by Hinton and Nowlan (1987) that behaves in a way that is consistent
with this conjecture.
Piattelli-Palmarini (1989) presents a different kind of
argument: grammar is not completely predictable as an adaptation to
communication, therefore it lacks design and did not evolve by selection. He
writes, "Survival criteria, the need to communicate and plan concerted
action, cannot account for our specific linguistic nature. Adaptation cannot
even begin to explain any of these phenomena." Frequently cited examples
of arbitrary phenomena in language
include constraints on movement (such as subjacency), irregular morphology, and
lexical differences in predicate-argument structure. For instance, it is
acceptable to say Who did John see Mary with?, but not Who did John see Mary
and?; John broke the glass but not John breaked the glass;John filled the glass
with milk, but not John poured the glass with milk. The arguments that language could not be an
adaptation take two forms: (i) language
could be better than it is, and (ii) language could be different than it is. We show that neither
form of the argument is valid, and that the facts that it invokes are perfectly
consistent with language
being an adaptation and offer not the slightest support to any specific
alternative.
In their crudest form, arguments about the putative
functionlessness of grammar run as follows: "I bet you can't tell me a
function for Constraint X; therefore language is a spandrel." But even if it could be shown
that one part of language
had no function, that would not mean that all parts of language had no function.
Recall from Section 2.2 that many organs contain modified spandrels but this
does not mean that natural selection did not assemble or shape the organ.
Worse, Constraint X may not be a genuine part of the language faculty but just a description of
one aspect of it, an epiphenomenal spandrel. No adaptive organ can be adaptive
in every aspect, because there are as many aspects of an organ as there are
ways of describing it. The recent history of linguistics provides numerous examples
where a newly-discovered constraint is first proposed as an explicit statement
listed as part of a grammar, but is then shown to be a deductive consequence of
a far more wide-ranging principle (see, e.g., Chomsky, 1981; Freidin, 1978.)
For example, the ungrammaticality of sentences like John to have won is
surprising, once attributed to a filter specifically ruling out [NP-to-VP]
sequences, is now seen as a consequence of the Case Filter. Although one might
legitimately wonder what good "*[NP-to-VP]" is doing in a grammar,
one could hardly dispense with something like the Case Filter.
Since the mere appearance of some
nonoptimal feature is inconclusive, we must examine specific explanations for
why the feature exists. In the case of the nonselectionist position espoused by
Piattelli-Palmarini, there is none: not a hint of how any specific aspect of
grammar might be explained, even in principle, as a specific consequence of
some developmental process or genetic mechanism or constraint on possible brain
structure. The position gains all its support from the supposed lack of an
adaptive explanation. In fact, we will show that there is such an explanation,
well-motivated both within evolutionary theory and within linguistics, so the
support disappears.
The idea that natural selection
aspires toward perfection has long been discredited within evolutionary theory
(Williams, 1966). As Maynard Smith (1984: 290) has put it, "If there were
no constraints on what is possible, the best phenotype would live forever,
would be impregnable to predators, would lay eggs at an infinite rate, and so
on." Tradeoffs among conflicting adaptive goals are a ubiquitous
limitation on optimality in the design of organisms. It may be adaptive for a
male bird to advertise his health to females with gaudy plumage or a long tail,
but not to the extent that predators are attracted or flight is impossible.
Tradeoffs of utility within language are also unavoidable
(Bolinger, 1980; Slobin, 1977). For example, there is a conflict of interest
between speaker and hearer. Speakers want to minimize articulatory effort and
hence tend towards brevity and phonological reduction. Hearers want to minimize
the effort of understanding and hence desire explicitness and clarity. This
conflict of interest is inherent to the communication process and operates at
many levels. Editors badger authors into expanding elliptical passages;
parsimonious headline writers unwittingly produce Squad Helps Dog Bite Victim
and Stud Tires Out. Similarly there is a conflict of interest between speaker
and learner. A large vocabulary allows for concise and precise expression. But
it is only useful if every potential listener has had the opportunity to learn
each item. Again, this tradeoff is inherent to communication; one man's jargon
term is another's mot juste.
Clearly, any shared system of
communication is going to have to adopt a code that is a compromise among these
demands, and so will appear to be arbitrary from the point of view of any one
criterion. There is always a large range of solutions to the combined demands
of communication that reach slightly different equilibrium points in this
multidimensional space. Slobin (1977) points out that the Serbo-Croatian
inflectional system is "a classic Indo-European synthetic muddle,"
suffixing each noun with a single affix from a paradigm full of irregularity,
homophony, and zero-morphemes. As a result the system is perfected late and
with considerable difficulty. In contrast the Turkish inflectional system is
semantically transparent, with strings of clearly demarcated regular suffixes,
and is mastered by the age of two. When it comes to production by an adult who
has overlearned the system, however, Serbo-Croatian does have an advantage in
minimizing the sheer number of syllables that must be articulated. Furthermore,
Slobin points out that such tradeoffs can be documented in studies of
historical change and borrowing. For example changes that serve to enhance
brevity will proceed until comprehension becomes impaired, at which point new
affixes or distinctions are introduced to restore the balance (see also
Samuels, 1972). A given feature of language
may be arbitrary in the sense that there are alternative solutions that are
better from the standpoint of some single criterion. But this does not mean
that it is good for nothing at all!
Subjacency -- the prohibition
against dependencies between a gap and its antecedent that spans certain
combinations of phrasal nodes -- is a classic example of an arbitrary
constraint (see Freidin & Quicoli, 1989). In English you can say What does
he believe they claimed that I said? but not the semantically parallel *What
does he believe the claim that I said?. One might ask why languages behave this
way. Why not allow extraction anywhere, or nowhere? The constraint may exist
because parsing sentences with gaps is a notoriously difficult problem and a
system that has to be prepared for the possibility of inaudible elements
anywhere in the sentence is in danger of bogging down by positing them everywhere.
Subjacency has been held to assist parsing because it cuts down on the set of
structures that the parser has to keep track of when finding gaps (Berwick and
Weinberg, 1984). This bonus to listeners is often a hindrance to speakers, who
struggle with resumptive pronouns in clumsy sentences such as That's the guy
that you heard the rumor about his wife leaving him. There is nothing
"necessary" about the precise English version of the constraint or
about the small sample of alternatives allowed within natural language. But by settling in
on a particular subset of the range of possible compromises between the demands
of expressiveness and parsability, the evolutionary process may have converged
on a satisfactory set of solutions to one problem within language processing.
The fact that one can conceive of a biological system being
different than it is says nothing about whether it is an adaptation (see Mayr,
1983). No one would argue that selection was not the key organizing force in
the evolution of the vertebrate eye just because the compound eyes of
arthropods are different. Similarly, pointing out that a hypothetical Martian language could do
passivization differently is inconclusive. We must ask how well-supported
specific explanations are.
In the case of features of human language structure that could
have been different, again Piattelli-Palmarini presents no explanations at all
and relies entirely on the putative inability of natural selection to provide any
sort of motivated account. But in fact there is such an account: the nature of language makes arbitrariness
of grammar itself part of the adaptive solution of effective communication in
principle.
Any communicative system requires a
coding protocol which can be arbitrary as long as it is shared. Liberman and
Mattingly (1989) call this the requirement of parity, and we can illustrate it
with the (coincidentally-named) "parity" settings in electronic
communication protocols. There is nothing particularly logical about setting
your printer's serial interface to the "even," as opposed to the
"odd," parity setting. Nor is there any motivation to set your
computer to odd as opposed to even parity. But there is every reason to set the
computer and printer to the same parity, whatever it is, because if you don't,
they cannot communicate. Indeed, standardization itself is far more important
than any other adaptive feature possessed by one party. Many personal computer
manufacturers in the 1980s boasted of the superior engineering and design of
their product compared to the IBM PC. But when these machines were not
IBM-compatible, the results are well-known.
In the evolution of the language faculty many "arbitrary"
constraints may have been selected simply because they defined parts of a
standardized communicative code in the brains of some critical mass of
speakers. Piattelli-Palmarini may be correct in claiming that there is nothing
adaptive about forming yes-no questions by inverting the subject and auxiliary
as opposed to reversing the order of words in the sentence. But given that language must do one or the
other, it is highly adaptive for each member of a community of speakers to be
forced to learn to do it the same way as all the other members. To be sure,
some combination of historical accidents, epiphenomena of other cognitive
processes, and neurodevelopmental constraints must have played a large role in
the breaking of symmetry that was needed to get the fixation process running
away in one direction or another. But it still must have been selection that
resulted in the convention then becoming innately entrenched.
The requirement of parity operates
at all levels of a communications protocol. Within individual languages the
utility of arbitrary but shared features is most obvious in the choice of
individual words: there is no reason for you to call a dog dog rather than cat
except for the fact that everyone else is doing it, but that is reason enough.
Saussure (1959) called this inherent feature of language "l'arbitraire du signe," and
Hurford (1989), using evolutionary game theory, demonstrates the evolutionary
stability of such a "Saussurean" strategy whereby each learner uses
the same arbitrary signs in production that it uses in comprehension (i.e.,
that other speakers use in production). More generally, these considerations
suggest that a preference for arbitrariness is built into the language acquisition device
at two levels. It only hypothesizes rules that fall within the (possibly
arbitrary) set defined by universal grammar, and within that set, it tries to
choose rules that match those used by the community, whatever they are.
The benefits of a learning
mechanism designed to assess and adopt the prevailing parity settings become
especially clear when we consider alternatives, such as trying to get each
speaker to converge on the same standard by endogenously applying some
rationale to predict form from meaning. There are many possible rationales for
any form-meaning pairing, and that is exactly the problem -- different
rationales can impress different speakers, or the same speakers on different
occasions, to different degrees. But such differences in cognitive style,
personal history, or momentary interests must be set aside if people are to
communicate. As mentioned, no grammatical device can simultaneously optimize
the demands of talkers and hearers, but it will not do to talk in
Serbo-Croatian and demand that one's listeners reply in Turkish. Furthermore,
whenever cognition is flexible enough to construe a situation in more than one
way, no simple correspondence between syntax and semantics can be used
predictively by a community of speakers to "deduce" the most
"logical" grammatical structure. For example, there is a simple and
universal principle dictating that the surface direct object of a causative
verb refers to an entity that is "affected" by the action. But the
principle by itself is unusable. When a girl puts boxes in baskets she is literally
affecting both: the boxes are changing location, and the baskets are changing
state from empty to full. One would not want one perceiver interested in the
boxes to say that she is filling boxes while another interested in the baskets
to describe the same event as filling baskets; no one would know what went
where. However by letting different verbs idiosyncratically select different
kinds of entities as "affected" (e.g., place the box/*basket versus
fill the basket/*box), and forcing learners to respect the verbs' wishes,
grammar can allow speakers to specify different kinds of entities as affected
by putting them in the direct object position of different verbs, with minimal
ambiguity. Presumably this is why different verbs have different arbitrary
syntactic privileges (Pinker,
1989b), a phenomenon that Piattelli-Palmarini (1989) describes at length. Even
iconicity and onomatopoeia are in the eye and ear of the beholder. The ASL sign
for "tree" resembles the motion of a tree waving in the wind, but in
Chinese Sign Language
it is the motion of sketching the trunk (Newport & Meier, 1985). In the
United States, pigs go "oink"; in Japan, they go "boo-boo."
Acquisition
The need for arbitrariness has
profound consequences for understanding the role of communicative function in language acquisition and language evolution. Many
psychologists and artificial intelligence researchers have suggested that the
structure of grammar is simply the solution that every child arrives at in
solving the problem of how to communicate with others. Skinner's reinforcement
theory is the strongest version of this hypothesis (Skinner, 1957), but
versions that avoid his behaviorism and rely instead on general cognitive
problem-solving abilities have always been popular within psychology. Both
Skinner and cognitive theorists such as Bates et al. (1989) explicitly draw
parallels between the role of function in learning and evolution. Chomsky and
many other linguists and psycholinguists have argued against functionalism in
ontogeny, showing that many aspects of grammar cannot be reduced to being the
optimal solution to a communicative problem; rather, human grammar has a
universal idiosyncratic logic of its own. More generally, Chomsky has
emphasized that people's use of language
does not tightly serve utilitarian goals of communication but is an autonomous
competence to express thought (see, e.g., Chomsky, 1975). If communicative
function does not shape language
in the individual, one might conclude, it probably did not shape language in the species.
We suggest that the analogy that
underpins this debate is misleading. It is not just that learning and evolution
need not follow identical laws, selectionist or otherwise. (For example, as
Chomsky himself has stressed, the issue never even comes up in clearer cases
like vision, where nobody suggests that all infants' visual development is
related to their desire to see or that visual systems develop with random
variations that are selected by virtue of their ability to attain the child's
goals.) In the case of language
the arguments of section 3.4 suggest that language evolution and language acquisition not only
can differ but that they must differ. Evolution has had a wide variety of
equivalent communicative standards to choose from; there is no reason for it to
have favored the class of languages that includes Apache and Yiddish, but not
Old High Martian or Early Vulcan. But this flexibility has been used up by the
time a child is born; the species and the language community have already made their
choices. The child cannot learn just any useful communicative system; nor can
he or she learn just any natural language.
He or she is stuck with having to learn the particular kind of language the species
eventually converged upon and the particular variety the community has chosen.
Whatever rationales may have influenced these choices are buried in history and
cannot be recapitulated in development.
Moreover, any code as complex and
precise as a grammar for a natural language
will not wear its protocol on its sleeve. No mortal computer user can induce an
entire communications protocol or programming language from examples; that's why we have
manuals. This is because any particular instance of the use of such a protocol
is a unique event accompanied by a huge set of idiosyncratic circumstances,
some relevant to how the code must be used, most irrelevant, and there is no
way of deciding which is which. For the child, any sentence or set of sentences
is compatible with a wide variety of very different grammars, only one of them
correct (Chomsky, 1965, 1975, 1980, 1981; Pinker, 1979, 1984; Wexler and Culicover, 1980).
For example, without prior constraints, it would be natural to generalize from
input sentences like Who did you see her with? to *Who did you see her and?,
from teethmarks to *clawsmarks, from You better be good to *Better you be
good?. The child has no manual to consult, and presumably that is why he or she
needs innate constraints.
So we see a reason why
functionalist theories of the evolution of language can be true while functionalist
theories of the acquisition of language
can be false. From the very start of language acquisition, children obey grammatical constraints
that afford them no immediate communicative advantage. To take just one
example, 1- and 2-year-olds acquiring English obey a formal constraint on
phrase structure configurations concerning the distinction between lexical
categories and phrasal categories and as a result avoid placing determiners and
adjectives before pronouns and proper names. They will use phrases like big dog
to express the belief that a particular dog is big, but they will never use
phrases like big Fred or big he to express the belief that a particular person
is big (Bloom, in press). Children respect this constraint despite the limits
it puts on their expressive range.
Furthermore, despite unsupported
suggestions to the contrary among developmental psychologists, many strides in language development afford
the child no locally-discernible increment in communicative ability (Maratsos,
1983, 1989). When children say breaked and comed, they are using a system that
is far simpler and more logical than the adult combination of a regular rule
and 150 irregular memorized exceptions. Such errors do not reliably elicit
parental corrections or other conversational feedback (Brown and Hanlon, 1970;
Morgan and Travis, in press). There is no deficit in comprehensibility; the
meaning of comed is perfectly clear. In fact the child's system has greater
expressive power that the adult's. When children say hitted and cutted, they
are distinguishing between past and nonpast forms in a manner that is
unavailable to adults, who must use hit and cut across the board. Why do
children eventually abandon this simple, logical, expressive system? They must
be programmed so that the mere requirement of conformity to the adult code, as
subtle and arbitrary as it is, wins over other desiderata.
The requirement that a
communicative code have an innate arbitrary foundation ("universal
grammar," in the case of humans) may have analogues elsewhere in biology.
Mayr (1982: 612) notes that
Behavior that serves as
communication, for instance courtship behavior, must be stereotyped in order
not to be misunderstood. The genetic program controlling such behavior must be
"closed," that is, it must be reasonably resistant to any changes
during the individual life cycle. Other behaviors, for instance those that
control the choice of food or habitat, must have a certain amount of
flexibility in order to permit the incorporation of new experiences; such
behaviors must be controlled by an "open" program.
In sum, the requirement for
standardization of communication protocols dictates that it is better for
nature to build a language
acquisition device that picks up the code of the ambient language than one that
invents a code that is useful from a child's eye view. Acquiring such a code
from examples is no mean feat, and so many grammatical principles and
constraints must be hardwired into the device. Thus even if the functions of
grammatical devices play an important role in evolution, they may play no role
in acquisition.
Given that the criteria for being an adaptation appear to be
satisfied in the case of language,
we can examine the strength of the competing explanations that language is a spandrel
suggested by Gould, Chomsky, and Piattelli-Palmarini.
The main motivation for Gould's specific suggestion that language is a spandrel is his
frequently-stated position that the mind is a single general-purpose computer.
For example, as part of a critique of a theory of the origin of language, Gould (1979: 386)
writes:
I don't doubt for a moment that the
brain's enlargement in human evolution had an adaptive basis mediated by
selection. But I would be more than mildly surprised if many of the specific
things it now can do are the product of direct selection "for" that
particular behavior. Once you build a complex machine, it can perform so many
unanticipated tasks. Build a computer "for" processing monthly checks
at the plant, and it can also perform factor analyses on human skeletal measures,
play Rogerian analyst, and whip anyone's ass (or at least tie them perpetually)
in tic-tac-toe.
The analogy is somewhat misleading.
It is just not true that you can take a computer that processes monthly checks
and use it to play Rogerian analyst; someone has to reprogram it first. Language learning is not
programming: parents provide their children with sentences of English, not
rules of English. We suggest that natural selection was the programmer.
The analogy could be modified by
imagining some machine equipped with a single program that can learn from
examples to calculate monthly checks, perform factor analyses, and play
Rogerian analyst, all without explicit programming. Such a device does not now
exist in artificial intelligence and it is unlikely to exist in biological
intelligence. There is no psychologically realistic multipurpose learning
program that can acquire language
as a special case, because the kinds of generalizations that must be made to
acquire a grammar are at cross-purposes with those that are useful in acquiring
other systems of knowledge from examples (Chomsky, 1982; Pinker, 1979, 1984; Wexler
and Culicover, 1980). The gross facts about the dissociability of language and other learned
cultural systems, listed in the first paragraph of this paper, also belie the
suggestion that language
is a spandrel of any general cognitive learning ability.
The theory that the mind is an all-purpose learning device
is of course anathema to Chomsky (and to Piattelli-Palmarini), making it a
puzzle that they should find themselves in general agreement with Gould.
Recently, Gould (1989) has described some common ground. Chomsky, he suggests,
is in the Continental tradition of trying to explain evolution by structural
laws constraining possible organic forms. For example, Chomsky writes:
In studying the evolution of mind,
we cannot guess to what extent there are physically possible alternatives to,
say, transformational generative grammar, for an organism meeting certain other
physical conditions characteristic of humans. Conceivably, there are none -- or
very few -- in which case talk about evolution of the language capacity is beside
the point. (1972: 97-98).
These skills [e.g., learning a
grammar] may well have arisen as a concomitant of structural properties of the
brain that developed for other reasons. Suppose that there was selection for
bigger brains, more cortical surface, hemispheric specialization for analytic
processing, or many other structural properties that can be imagined. The brain
that evolved might well have all sorts of special properties that are not
individually selected; there would be no miracle in this, but only the normal
workings of evolution. We have no idea, at present, how
10 physical laws apply when 10
neurons are placed in an object the size of a basketball, under the special
conditions that arose during human evolution. (1982: 321)
In this regard [the evolution of
infinite digital systems], speculations about natural selection are no more
plausible than many others; perhaps these are simply emergent physical
properties of a brain that reaches a certain level of complexity under the
specific conditions of human evolution. (1988b: 22 in ms.)
Although Chomsky does not literally
argue for any specific evolutionary hypothesis, he repeatedly urges us to
consider "physical laws" as possible alternatives to natural
selection. But it is not easy to see exactly what we should be considering. It
is certainly true that natural selection cannot explain all aspects of the
evolution of language.
But is there any reason to believe that there are as-yet undiscovered theorems
of physics that can account for the intricate design of natural language? Of course human
brains obey the laws of physics, and always did, but that does not mean that
their specific structure can be explained by such laws.
More plausibly, we might look to
constraints on the possible neural basis for language and its epigenetic growth. But neural
tissue is wired up by developmental processes that act in similar ways all over
the cortex and to a lesser degree across the animal kingdom (Dodd and Jessell,
1988; Harrelson and Goodman, 1988). In different organisms it has evolved the
ability to perform the computations necessary for pollen-source communication,
celestial navigation, Doppler-shift echolocation, stereopsis, controlled
flight, dam-building, sound mimicry, and face recognition. The space of
physically possible neural systems thus can't be all that small, as far as
specific computational abilities are concerned. And it is most unlikely that
laws acting at the level of substrate adhesion molecules and synaptic
competition, when their effects are projected upward through many levels of
scale and hierarchical organization, would automatically result in systems that
accomplish interesting engineering tasks in a world of medium-sized objects.
Changes in brain quantity could
lead to changes in brain quality. But mere largeness of brain is neither a
necessary nor a sufficient condition for language, as Lenneberg's (1967) studies of
nanencephaly and craniometric studies of individual variation have shown. Nor
is there reason to think that if you simply pile more and more neurons into a
circuit or more and more circuits into a brain that computationally interesting
abilities would just emerge. It seems more likely that you would end up with a
very big random pattern generator. Neural network modeling efforts have
suggested that complex computational abilities require either extrinsically
imposed design or numerous richly structured inputs during learning or both (Pinker & Prince, 1988;
Lachter & Bever, 1988), any of which would be inconsistent with Chomsky's
suggestions.
Finally, there may be direct
evidence against the speculation that language is a necessary physical consequence of how human
brains can grow. Gopnik (1990a, b) describes a syndrome of developmental
dysphasia whose sufferers lack control of morphological features such as
number, gender, tense, and case. Otherwise they are intellectually normal. One
10-year-old boy earned the top grade in his mathematics class and is a
respectable computer programmer. This shows that a human brain lacking
components of grammar, perhaps even a brain with the capacity of discrete
infinity, is physically and neurodevelopmentally possible.
In sum, there is no support for the
hypothesis that language
emerges from physical laws acting in unknown ways in a large brain. While there
are no doubt aspects of the system that can only be explained by historical,
developmental, or random processes, the most likely explanation for the complex
structure of the language
faculty is that it is a design imposed on neural circuitry as a response to evolutionary
pressures.
5. The Process of Language Evolution
For universal grammar to have
evolved by Darwinian natural selection, it is not enough that it be useful in
some general sense. There must have been genetic variation among individuals in
their grammatical competence. There must have been a series of steps leading
from no language at
all to language as
we now find it, each step small enough to have been produced by a random
mutation or recombination, and each intermediate grammar useful to its possessor.
Every detail of grammatical competence that we wish to ascribe to selection
must have conferred a reproductive advantage on its speakers, and this
advantage must be large enough to have become fixed in the ancestral
population. And there must be enough evolutionary time and genomic space
separating our species from nonlinguistic primate ancestors.
There are no conclusive data on any
of these issues. However this has not prevented various people from claiming
that each of the necessary postulates is false! We argue that what we do know
from the biology of language
and evolution makes each of the postulates quite plausible.
Lieberman (1984, 1989) claims that the Chomskyan universal
grammar could not have evolved. He writes:
The premises that underlie current
"nativist" linguistic theory
... are out of touch with modern
biology. Ernst Mayr (1982), in his definitive work, The Growth of Biological
Thought, discusses these basic principles that must structure any biologically
meaningful nativist theory. ... [one of the principles is:] Essentialistic
thinking (e.g., characterizing human linguistic ability in terms of a uniform
hypothetical universal grammar) is inappropriate for describing the biological
endowment of living organisms. (1989: 203-205)
A true nativist theory must
accommodate genetic variation. A detailed genetically transmitted universal
grammar that is identical for every human on the planet is outside the range of
biological plausibility. (1989: 223)
This is part of Lieberman's
argument that syntax is acquired by general-purpose learning abilities, not by
a dedicated module or set of modules. But the passages quoted above contain a
variety of misunderstandings and distortions. Chomskian linguistics is the
antithesis of the kind of essentialism that Mayr decries. It treats such
disembodied interindividual entities as "The English Language" as unreal
epiphenomena. The only scientifically genuine entities are individual grammars
situated in the heads of individual speakers (see Chomsky, 1986, for extended
discussion). True, grammars for particular languages, and universal grammar,
are often provisionally idealized as a single kind of system. But this is
commonplace in systems-level physiology and anatomy; for example the structure
of the human eye is always described as if all individuals shared it and
individual variation and pathology are discussed as deviations from a norm.
This is because natural selection, while feeding on variation, uses it up
(Ridley, 1986; Sober, 1984). In adaptively complex structures in particular,
the variation we see does not consist of qualitative differences in basic
design, and this surely applies to complex mental structures as well (Tooby and
Cosmides, 1989).
Also, contrary to what Lieberman
implies, there does exist variation in grammatical ability. Within the range
that we would call "normal" we all know some individuals who
habitually use tangled syntax and others who speak with elegance, some who are
linguistically creative and