Harnad, Stevan (2008) 'Why and
How the Problem of the Evolution of Universal Grammar (UG) is Hard' Behavioral
and Brain Sciences (forthcoming);
Commentary on Christiansen, Morten H. and Chater, Nick (2008) "Language
as
Shaped by the Brain" Behavioral and Brain Sciences (forthcoming) http://www.bbsonline.org/Preprints/Christiansen-12292006/
[Note: This is the shorter, published version.
Please click on the longer version to see the full text.]
Why and How the Problem of the Evolution of
Universal Grammar (UG) is Hard
Stevan Harnad
Chaire de recherche du Canada
Institut des sciences cognitives
Universite du Quebec a Montreal
Montreal, Quebec, Canada H3C 3P8
Department of Electronics and Computer Science
University of Southampton
Highfield, Southampton
SO17 1BJ UNITED KINGDOM
http://www.ecs.soton.ac.uk/~harnad/
Abstract: Christiansen & Chater suggest that language is an organism, like us, and our brains were not selected for UG capacity; rather, languages were selected for learnability with minimal trial and error experience by our brains. This explanation is circular: Where did our brains' selective capacity to learn all and only UG-compliant languages come from?
Keywords: Language,
Evolution, Poverty of the
Stimulus,
Evolution, Universal Grammar, Chomsky
The problem of the evolutionary
origins of Universal Grammar (UG) is not as readily solvable as
Christiansen
& Chater (C&C) suggest.
UG is a
complicated set of grammatical rules,
but not the ones we learned in school. We were never taught them, we
are not
aware them, we cannot put them into words, and we would not recognize
them if
they were explicitly told to us by a professional grammarian. Yet we
all 'know'
the rules of UG "implicitly," because they are the rules that make us
able to produce all and only the sentences that are grammatically
well-formed,
according to UG. It's rather as if we all knew implicitly how to play
chess --
we could make all and only the legal moves -- yet we had no explicit
idea what
rules we were following.
The rules of
chess, however, are simple, we
learned them, and we can verbalize them. UG's rules are abstract,
complex and
technical. Since Chomsky first discovered their existence, linguists
have
gradually been figuring them out through decades of hypothesis, trial,
and
error, guided by the grammatical intuitions we all share about what can
and
cannot be said. The result is a set of rules that allow all and only
the
sentences we all recognize as well-formed and disallow all those we
recognize
as ill-formed. That set of rules turned out to have some surprising
properties:
UG turned out to be universal: All languages obey the very same set of
rules.
But the most surprising thing of all was that children do not learn the
rules
of UG itself.
Children
cannot learn the rules of UG because
they are too complicated to learn by observation and trial and error on
the
basis of the information available to the language-learning child. Nor
are they
taught by explicit instruction: Before Chomsky no one even knew the
rules, let
alone taught them, even though our species had been speaking language
for a
hundred thousand years.
The reason
the child cannot learn UG is that the data from which the rules of UG would have to be
learned do not contain anywhere near enough of the information to infer
the
rules from them. This is called
the Ôpoverty of the stimulus'. In
order to be learned at all, the rules of UG would have to be learnable
through
trial and error, with error-correction, just as chess-rules have to be,
when we
learn them without explicit instruction: I try to move my bishop in a
certain
way, and you tell me, no, that's not a legal move, this is, and so on.
Children
cannot learn the rules of UG that way because they basically never make
(or
hear) any UG errors ('wrong moves'). Hence children never get or hear
any UG
error-corrections.
It is not
that children speak flawlessly from birth. But the little the child
experiences
during the relatively brief period of transition from being unable to
speak to
being able to speak does not involve any errors (or
error-corrections) in
the rules of UG,
either from the child or from the speakers that the child hears. There
are
conventional grammatical errors and corrections aplenty, but no UG
violations
produced, heard, or corrected. UG rules are never broken, never
corrected,
hence never "learned": Therefore they must already have been inborn.
But that
raises the hard question of the evolutionary origin of those inborn
rules.
Evolution has
more time available than the child, but it has an even more
impoverished
database: What would serve as error-correction, and what would count as
right
and wrong, in order to shape UG in the usual Darwinian way, through
trial-and-error genetic variation
and selective retention, based on advantages in survival and
reproduction?
In explaining the
origins of other complex biological structures, such as fins,
wings or
eyes, or biological functions such as the capacity to see, learn, or
reason,
there is no problem in principle for the usual kind of evolutionary
trial-and-error explanation. But with UG there is a deep problem in
principle (Harnad 1976).
The problem is not just UG's complexity but that UG has no apparent
adaptive
advantages. For
although a professional grammarian's lifetime is long enough to work
out most
of UG's rules explicitly by trial and error induction, it turns out
that (with
the possible exception of a few small portions of UG governed by
optimality
constraints) no logical or practical advantage has yet been
discerned that
favors what UG allows over what it disallows, or over an altogether
different
set of grammatical rules
(perhaps even a much simpler and learnable set).
C&C
rightly express skepticism about alternative 'piggy-back' theories of
the
evolutionary origin of UG. There is no credible 'precursor' with a
prior
adaptive advantage of its own that could later have been 'co-opted' to
do the
duties of UG as well. But C&C's alternative proposal is no more
convincing: C&C say that language, too, is an 'organism,' like
people and animals,
that it
too varies across generations, historically, and that the shape that
language
took was selectively determined by the shape the brain already had, in
that only
the languages that were learnable by our brains successfully 'survived
and
reproduced.'
The trouble
with this hypothesis is that it is circular: We were looking for the
evolutionary origin of the complex and abstract rules of UG. C&C
say (based
on their computer simulations of far simpler rule systems, not bound by
the
poverty of the stimulus): Don't ask how the UG rules evolved in the
brain. The
rules are in language, which is another 'organism, ' not in the brain.
The
brain simply helped shape the language, in that the variant languages
that were
not learnable by the brain simply did not 'survive.'
This
hypothesis begs the question of why and how the brain acquired an
evolved
capacity to learn all and only UG-compliant languages in the first
place,
despite the poverty of the stimulus – which was the hard problem we
started out with in the first place! It would be like saying that the
reason we
are born already knowing the rules of chess without ever having to
learn them
by trial and error is that, in our evolutionary past, there was
variation in
the games (likewise 'organisms') that we organisms tried to play, and
only
those games that we could play without having to learn them by trial
and error
survived! (That still would not even begin to explain what it is about
our
brains that makes them able to play chess without trial and error!)
This
circularity is partly a result of a vagueness about what exactly is the
target
of language evolution theory. Pinker & Bloom (1990) had already
begun the misleading
practice of freely conflating evolutionarily unproblematic questions
(such as
the origins of phonology, learnable aspects of grammar, vocabulary,
'parity')
with the one hard problem of the origins of UG, which specifically
concerns
the evolutionary origins of complex rules that are unlearnable because
of the
poverty of the stimulus.
Language, after all, is not just grammar, let alone just UG. If, on
the one hand, the adaptive value of language itself (Cangelosi &
Harnad
2001; Harnad 2005, 2007) could have been achieved with a much simpler
grammar
then UG (perhaps even a learnable one), then the evolutionary origin
and
adaptive function of UG becomes all the harder to explain, with
C&C's
historical variation in the language 'organism' occurring far too late
in the
day to be of any help. If, on the other hand, the adaptive advantages
of
language were impossible without UG, then we are still left with the
hard
problem of explaining how and why not.
Chomsky
(2005) himself has suggested that UG may be a necessary property of being able to think at
all. He has been right about so much
else that this possibility definitely needs to be taken seriously. But
to solve
the hard problem it would also have to explain how UG is logically or functionally
necessary in order to be able to think at all.
NOTE: Unabridged draft of this
commentary: http://cogprints.org/6008/
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