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The Consequences of Language: The Biological Basis For Language?
Chapter 4a Page 1
The Consequences of Language
Chapter 4. The biological Basis of Language
The purpose of this chapter is to provide an evolutionary perspective of the evolution of biological structures that
enable language.
Questions about the Origin and Evolution of Language; Establishing a Biological Perspective; How did the vocal
tract develop? How did the brain develop? (include contributions of cognitive neuroscience to this understanding.;
The Evolution of Language Structure
1.
Questions about the Origin and Evolution of Language
Because language is one of the most salient features that separates humans from other
animals, the origin and evolution of language has been and remains a crucial question for it may
provide important insights into what we are as human beings and how we got that way. One of
the earliest recorded views of language origins is the biblical story of Babel. According to this
view, people wanted to build a tower so tall that they could come closer to God. God considered
this a poor idea and declared that the people should speak different languages to make it
impossible for them to communicate and thus prevent them from building the tower.
In 1855, The Linguistic Society of Paris proclaimed that they were no longer going to
publish articles that addressed questions of language origins, as the papers previously submitted
and published were highly speculative and the evidence upon which they were based extremely
limited. As a result, they concluded that they concluded that it was all a waste of time, because
such theories, while interesting, did not advance our understandings of language origins beyond
the earlier biblical explanation.
Since that time, the question has been reopened with Hockett’s 1960 Scientific American
article on the origin and evolution of language. Hockett’s article brought out that today we now
have much more information at our disposal than did the French linguistics writing for the
Linguistic Society of Paris in 1855 and, just as importantly, we have different ways of
approaching the question than we did earlier. For example, we now have a richer understanding
of evolution, note that Darwin published his theory of evolution in The Origin of the Species in
1859. We now have a richer fossil record of our human ancestors, an understanding of how
language structure works, along with that an understanding of how the vocal tract and the brain
contribute to the production and comprehension of language. Comparative anatomy helps us to
understand how our anatomy differs from our nearest phylogenetic relatives. These
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developments surely justify the reopening of the investigation of the origin and evolution of
language.
It may be noted that in the biblical version of language origins, it was assumed that Adam
and Eve (and possibly God) spoke a language quite similar to that spoken today, though we do
not know what that language was, nor what it looked like. While the Babel story accounts for
the diversification of language, it does not recognize any sort of evolution from some earlier
form. However, from an evolutionary perspective, one would not expect modern human
language to emerge as a full-blown set of semiological systems, but rather develop in stages, as
did the human physical form. This chapter explores the evolution of the biological capacity for
language. We return to the question of the evolution of the semiological system in chapter 15.
Establishing a biological perspective
Physical anthropology, one of the four branches of anthropology seeks to understand the
physical (biological) evolution of our species. This perspective asks us to stand back and look at
ourselves as animals, to be sure different from other animals, but animals just the same. We
know that human beings, technically known as homo sapiens sapiens (= wise, wise humans), are
most closely related to the great apes and specifically the chimpanzees sharing a common
ancestor (known as Dryopithecus) who lived some 40 million years ago. Even now, we share a
large amount of our DNA (approximately 99%) with chimpanzees. One of the questions
physical anthropology asks is: to what extent are we dependent on our biology for our language
ability? To answer this question we explore, in this chapter, the workings and evolution of two
of the major organs of speech, the vocal tract and the brain. In the next chapter, we explore,
what Chomsky refers to as another organ of speech, the faculty of language.
Questions about the evolution of human language
Since the project of gaining a better understanding of how human language evolved is a
very formidable task involving the bringing together a lot of different information in new ways,
and a lot of speculation, one might ask, “why study this question?” In addition to understanding
how we evolved to what we are today, there are at least two important responses to this question.
First, understanding the role that language has played in our biological evolution will help us
understand who we are as humans. Secondly, it can also help gain a better understanding of the
nature of language.
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In this context, we need to recognize that we are not simply interested in when language
began, but also we are interested in the process of how a system of communication, which must
have been quite similar to that of present day chimpanzees (our nearest phylogenetic ancestor),
evolved into the complex semiological system today, one consisting of three different sign
systems (lexical, representational and syntactic). In addition, we want to understand how our
current bodily structure reflects adaptation to language as well. And finally we want to
understand what sort of relationship exists between the languages of today.
Purposefulness of adaptation and evolution
We begin with a discussion of the basics of evolutionary thinking as a foundation on
which to build an appreciation for the evolution of the brain and vocal tract. Within this
framework, the fundamental principle is that evolution does not have a direction or a purpose.
This is because evolution is the product of two evolutionary activities: random mutation and
selection.
Normal DNA reproduction. At the heart of genetic change is genetic reproduction. Every living
thing is composed of fundamental building blocks known as DNA. Under normal conditions this
DNA is reproduced (duplicated) without change, when the body grows new cells, either to
replace dead or damaged cells in the organism’s own body or when developing reproductive
cells which can produce new members of the species.1 This process of duplication is by far the
most common process occurring unceasingly, millions of times a day in an organism until death.
Random Mutation Occasionally however, something interferes with this normal process and the
copied DNA may be slightly different from the original and the DNA can be said to be mutated.
This process of mutation is termed random because one cannot predict either what part of the
DNA will mutate, when it will mutate, or what it will mutate into. In these cases, the mutated
DNA will cause a change in the cell and this may affect the viability of the cell so that it
functions less well or not at all and consequently the cell (but not necessarily the organism) dies.
Occasionally the cell with the mutated DNA survives.
Natural selection. When the altered DNA is part of a chromosome, the mutation can be passed
on to future generations. This is where the process known as selection goes to work. Selection
1
The exact process of how DNA is copied is beyond the scope of this book as is the question of what causes
mutation; however, it is generally known that toxic chemicals, and radiation are two of the key contributors to DNA
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is a process which statistically favors individuals and groups with a specific genetic make up, if
that make up proves successful in the given environment. If a mutation lessens the organism’s
ability to adapt to the environment then the organism and its genetic material is less likely to
survive. On those infinitesimally rare occasions that the mutation assists in adaptation, the
individuals carrying that genetic material are more likely to survive than those without it and as a
result, the percentage of individuals in the population carrying that mutation will increase.2
Direction and Progress. The long-horned grasshopper
pictured sitting on the right looks like an ordinary insect that
has been the product of random mutation and selection just
like any other animal. However, one will see that it has a
special organ on its forelegs; this is an organ for hearing,
commonly called an ear.
This strikes most of us as unusual for we expect to find ears in one’s head and some have
argued (wrongly) that the ears are on the head so that they can be close to the brain. But finding
hearing organs elsewhere on the body, should not be surprising when we recall the key points
about evolution supported by the processes of random mutation and selection. One of the
consequences of this process is that evolution does not have a direction, and consequently we
cannot talk of progress, only change. While it is no doubt true that being able to hear would be
likely to increase one’s adaptability and hence one might find in nature a variety of hearing
organs that have evolved in different ways, this does not argue for the inevitability for hearing
organs. Because evolution lacks a direction, we cannot predict what will happen next. We can
however trace the “history” of the evolutionary developments to see how we got to where we are
today. In this chapter we will examine three evolutionary developments that are related to
writing: the evolution of writing, the evolution of the vocal tract and the evolution of the brain.
When we carry this perspective over to the evolution of the organs of speech, we will see
that they too support the principles that development of language is not inevitable.
2. How did the Vocal Tract develop?
The primary representational system of human language uses the acoustic channel. More
mutation.
2
Because the evolutionary process is a dialectical one, one cannot determine in advance what features will be chosen
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precisely it is vocal which means that it uses the vocal apparatus. But what is this vocal tract and
what makes’s it so remarkable? Etymologically speaking, the word vocal is related to the words
vowel and voice. And not too surprisingly, vowels are the most salient component of the human
voice, that is speech. I say this, because when we hear human language, we rely most heavily on
hearing the vowels, for once they are identified we can identify the consonants with which they
are associated (note that consonants mean literally ‘with sonants’ (i.e., vowels). Thus before we
can examine the evolution of the vocal tract, we need to understand what vowels are and how
they are produced.
The Nature of Vowels
Listen to the vowels in the following words: beet /bit/, bit /bIt/, bait /bet/, bet /bt/, bat
/bæt/, bought /bt/, but /bt/, Bert /bt/, boat /bot/ boot /but/.
Notice, that when you hear these
vowels, your perception is probably that they are discrete entities quite different from each other.
Yet in the physical world, vowels are much like colors, there is a wide range of variation in type,
but when we identify them as part of a system, we see them as discrete entities: we see seven
basic colors and hear ten distinct vowels. This is
because, as was pointed out in chapter 3, these
vowels (in English) represent discrete, phonemic
contrasts called phonemes.
The adjacent figure shows the distribution
of one speaker’s production of the various vowels
in a reading of a short text. The vowels were
drawn by graphing the frequencies (given in kilo
Herz) of the first formant (horizontal axis) and
second formant (vertical axis). Although the
vowel tokens for each vowel are in the same
general area, one can see that there is a good deal
of variation in the production of each vowel phoneme.
Acoustically speaking, formant is a concentration
for selection. It is only after the adaptation has taken place that this becomes apparent.
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of sound energy in the sound spectrum. For example, as shown in the spectrogram3 in the
sidebar, the vowel /i/ as in the word beet has a first formant somewhere between 200 and 300
Herz and a second formant around 2000 to 3000 Herz. If we were to drop the second formant to
somewhere between 600 and 1200 Herz without changing the first formant, we would recognize
the sound as the vowel /u/ as in boot. If we were to raise the first formant to around 800 to 1000
Herz and drop the second formant to around 1000 to 1200 Herz, we would hear the vowel /a/ as
in hot.
How are formants produced acoustically?
The source-filter theory offers a straightforward explanation of how formants are
produced. The source refers to the source of the sound to be filtered, while the filter is a tube
which acts to reinforce some frequencies and dampen others. According to this theory, sound is
produced by a vibrating object, a larynx, a violin string, etc. The most prominent sound is the
fundamental frequency. When we hear an "A" on the piano, we recognize it as an "A" because
of its fundamental frequency. In addition, most sounds are not single waveforms, but consist of
multiple waves of differing frequencies and amplitudes. For example, in addition to the
fundamental frequency of a sound (the
one which gives its characteristic pitch)
are a set of harmonics, each of which
have is a sound wave whose frequency
is a multiple of the fundamental
frequency. These harmonics arise
because of the physical properties of the
vibrating sound source and are what
make a piano sound different from a
violin, a trumpet or a human voice.
The musical note "A" has a fundamental frequency of 446 Herz (cycles per second). By
cycles per second, we mean the number of cycles that a sound accomplishes each second - the
more cycles, the higher the frequency. To understand what a cycle is, we need to recognize that
A sound spectrogram is a “sound graph” showing the concentration of sound by frequency on the vertical axis and
time on the horizontal axis.
3
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sound only exists by traveling through a medium (air, water, etc.). It does so as a wave, that is,
as a sequence of compressions and expansions (see figure 5).
The speed of sound traveling through air is
relatively constant, about 35,000 cm/sec or
Frequency = 35,000 cm/sec (Speed of Sound)
Length of Wave
roughly 600 mph (it travels through water much more rapidly than it travels through air). The
formula in the adjacent box expresses an important relationship between the frequency of a
sound and the length of wavelength: the higher the frequency the shorter the wavelength. This
relationship is one of the two basic principles behind the sound filter for it shows that sounds of
different frequencies will have different wavelengths. The second principle has to do with fit,
that is some wavelengths will fit a given filter and will thus be "reinforced" while wavelengths
which do not fit will be destroyed "filtered out." The wavelengths that fit are called formants.
From the above two principles, it follows that the basis for the fit is the length of the
filter. A wavelength that fits will be equal to the length of the filter or some fraction or multiple
of the length of the filter. Thus when an array of wave lengths is introduced to a sound filter, for
example when blowing on a beer bottle, only those waves which "fit" will be reinforced and
therefore heard. By removing some of the beer from the bottle (in the interest of science), we
lengthen the filter thereby increasing the length of the wave which fits in the filter. As the
equation in the above box expresses, a longer wave means a lower frequency, which is why we
hear a lower pitch (frequency).
It also follows that a filter is nothing more than a tube with its length determining which
waves will resonate (fit) and which will not. Note that the frequency of a wave can be calculated
using the above formula. Actually this works for a filter (tube) which is closed at both ends. If
the tube is open at one end, the wavelength is doubled and if the tube is open at both ends, the
wavelength is quadrupled.
How does the vocal tract produce these formants?
The human vocal tract is also a sound filter. More specifically it is a 17-centimeter tube
open at both ends. If unrestricted, this means that the vocal tract would support a wavelength
(formant) of fours times (owing to its being open at both ends) its 17-centimeter length or 68 cm.
To find the frequency of this formant we divide this number into the speed of sound in air
(35,000 cm/sec) with the result of 470 Herz. (The calculation of the second formant is a bit more
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complicated.)
Figure 6 shows a spectrograph of the vowel "schwa,” the
vowel found in the words, cut, fuss and putt. The line at the 150
Herz level represents the fundamental frequency and the bars at
500 Herz and 1500 represent the first and second formants
respectively. Note that the first formant is at 500 cm, which is
what was calculated for an unrestricted tube 17 cm long and open
at both ends. In fact, additional calculations would confirm that
the second formant for an unrestricted tube open at both ends
would be at 1500. Thus, the schwa is the vowel produced by an
unimpeded tube 17 cm long and open at both ends.
The most important thing to remember about this section is that we identify vowels by
the frequencies of their first two formants, and that the
source-filter theory shows that formant production is
primarily a function of the length of the resonating tube.
But somewhat surprisingly, the schwa is not a
particularly common vowel in human language. The
three most common vowels in human language, also
known as the cardinal vowels [I] (ee), are [a] (ah) and [u]
(oo). Furthermore, the human vocal tract is that it is
configured in such a way that these are the three easiest
vowels to produce, physiologically and acoustically.4
As mentioned above, the human vocal tract is a 17-centimeter long tube bounded at one
end by the larynx and at the other by the lips (figure 7). The larynx, commonly called "the voice
4
What makes the universality of these three vowels even more remarkable is that it is not uncommon for the vowels
of a language to shift in value, that is, in their relative formant locations. Occasionally this results in a system where
one of the cardinal vowels is missing. For example, in Navajo, the high, back, rounded vowel is phonetically the [o]
instead of the typical [a] so that the three contrastive vowels in Navajo, for example, are /i/, /a/ and /o/. On the other
hand, in English, where the /u/ sound also shifted, another sound, in this case the /o/ shifted to take its place. Thus
the English word boot was at one time pronounced like the vowel in the word go, whereas now it has the /u/ sound.
This is also why we use the graphic [oo] to represent the /u/ sound in English. (Note: in transcription the square
brackets identify the phonetic character of sounds, without reference to a specific language system, whereas the
slanted brackets mark contrastive sounds (phonemes) within the system of a language such as in the Navajo
example.
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box" injects sound into the vocal tract by vibrating in the range of 100 to 300 Herz using air
expelled from the lungs. The lips can lengthen the vocal tract slightly, constrain it or even block
it completely. The tongue has the capacity to change the shape and most importantly the length
of the vocal tract. In fact, the tongue can divide the vocal tract into to different tubes known as
the oral cavity and the pharyngeal cavity.
However, unlike the straight 17-cm tube that produced the vowel schwa, the human vocal
tract is said to consist of two tubes: one, the most visible, known as the oral cavity, and the other
known as the pharynx. These are marked in the above diagram. The tongue plays a key role in
the two-tube vocal tract for it 1) makes it possible to divide the vocal tract into two connected,
resonating tubes of equal length instead of one and 2) it can determine the length of each tube
independently.
With this set up, the vowel [a] is produced by a narrowing of the pharynx and an opening
of the oral cavity. (This is why the doctor asks you to say “ah.” This enables him or her to get a
tongue depressor to the back of your oral cavity and press down on the tongue and take a look at
your pharynx, which often becomes inflamed at the onset of a cold. The articulation of the
vowel [i] is the reverse of [a]. There is a constriction of the oral cavity, but not that of the
pharyngeal cavity. Lastly, the vowel [u] involves a narrowing of the back half of each of these
resonating tubes and a slight, but significant lengthening of the oral cavity caused by the
rounding of the lips. Thus the ease with which the cardinal vowels of human language are
produced is a consequence of the two equal-length tube configuration of the human vocal tract.
The articulations of other vowels produced by the vocal tract involve variations or modifications
of these schematics.
The discussion of the
evolution of the vocal tract has
focused on its capacity to produce
vowels because the acoustic
recognition of consonants, as their
name "con-sonant" suggests, is
dependent upon an accompanying
vowel. As we say in chapter 3, a consonant can be described in terms of how the oral cavity is
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obstructed: in the case of /d/ the front of the tongue rises up to a position behind the teeth to
temporally block the flow of air through the oral cavity. Acoustically, a consonant is detected
from the way it attenuates the first and second formats as shown in figure 9.5
When did the vocal tract evolve?
Most physical
anthropologists tend to agree with
the claim that the evolution of the
human vocal tract involved the
development of a two-tube vocal
tract. Prior to that times, humans
and human ancestors, as inferred
from their fossil remains had
virtually no pharynx. This is also true of the great apes today and of newborn children as shown
in the sidebar. Many anthropologists believe that the elongation of the pharynx began with the
development of upright posture some 4.5 million years ago. Prior to upright posture, the tube
connecting the larynx and the mouth was more or less straight (see picture), but upright posture,
forced the head to bend forward causing a bend in the "vocal" tract and thereby creating for the
first time a second resonating chamber now known as the pharynx.
This second resonating chamber the pharynx enriched the potential of the "vocal tract" to
produce distinct sound for subsequent evolution resulted in the lengthening of the pharynx until
it achieved the same length as the oral cavity. Although there is fossil evidence for this evolution
as long ago as 300,000 years, most would agree that the two-tube, equal length vocal tract was in
place some 50,000 years ago or so at around the time of the transition from Homo-sapiens
Neanderthalensis (Neanderthal) to Homo-sapiens (modern human). In fact, it has been noted
(Brace) that one of the major differences between these two types is not brain size which is more
or less the same, but head shape, with modern man having a higher forehead as a result of the
final shortening of the oral cavity to achieve the two tube vocal tract. That is, the shortening of
the oral cavity involved the shortening of the front part of the skull including the front part of the
5
We note in passing that there is a small area of the brain, about one centimeter in diameter, that is dedicated to the
recognition of consonants. If this area is damaged, the individual loses the ability to identify them in speech.
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brain cavity. In order for the brain cavity to retain the same volume the skull increased
vertically.
The Faculty of Language
Early attempts to teach language to chimpanzees were doomed to failure because of the
different acoustical properties arising from the different vocal tract anatomies of chimpanzees
and humans. The simple fact that chimpanzees do not possess a two-tube vocal tract prohibits
them from producing the human vocal array. Yet despite their anatomical inability to produce
human vocal signs, Chimpanzees have shown the capacity to learn the representational signs of
sign language which are gestures rather than phonemes. This has enabled them to produce
lexical signs and string these lexical signs together. But while chimps can string lexical signs
together, I argue (Dwyer 1986) that this ability does not represent true syntax in the sense that
chimpanzees are not spelling out syntactic signs using parts of speech, but rather that this level of
(tactic) signing is paratactic. By parataxis I mean, a sentence consisting of two words which are
juxtaposed without the specificity of meaning as was characterized above for syntax. I will also
argue later that syntax can achieve a much higher level of precision that parataxis and that such
precision permits things like legitimation to take place.
The organs of speech
The evolution of the vocal tract involved the modification of a number of organs that
previously had no speech function whatsoever.
Organ
Non-speech Function
Speech Function
Evidence of Change
Lungs
Larynx
sound energy source
sound source
Tongue
breathing
protecting lungs, rigidifying
thorax
tasting, swallowing
larger in volume
smaller in size, narrower in diameter,
more efficient sound source.
more flexible in humans
lips
closing the mouth
Pharynx
virtually nonexistent in non
humans
protecting larynx
Epiglottis
controls shape of the oral and
pharyngeal tubes
lip rounding (can lengthen and change
tube’s acoustic properties
provides second tube for the 2-tube
vocal tract
no language function
evidence of it’s having evolving for at
least 300,000 years
currently dysfunctional in adult
humans
Because these are all soft tissue, it is difficult to detect their presence and hence change in
the palentological record. However, in comparison to other species, we note the following:
1. The Sound Source
a. The lungs have increased in volume, though not in their oxygen absorbing capacity. This would enable humans
to sustain sound longer than non-humans and hence speak longer.
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b. The larynx (voice box) is smaller in diameter than the “windpipe.” While this would make it more difficult to
draw in air for breathing, it would require less energy to produce sound and hence also allow humans to sustain
sound longer than non-humans.
2. The filter.
a. The tongue is thicker and more flexible in humans and enables the control of the shape of
both the oral cavity
b. The capacity of the lips to round and lengthen also appears in chimpanzees, which enables
them to “hoot” (produce “[u]-like sounds) though these sounds do not involve a two-tube
vocal tract.
c. The pharynx is virtually nonexistent in non-humans began evolving with upright posture.
The development of the pharynx provided a second filter which enabled the two tube vocal
tract.
d. The epiglottis in other animals sits directly over the larynx and protects the larynx and
windpipe during swallowing. When the pharynx lengthened, the epiglottis was drawn away
form the larynx and is currently dysfunctional in modern adult humans.
3. The brain, too, could be considered an organ of speech, as we shall see in the next section.
3. Language and the Brain.
The Modular Principle
In this chapter, we have adopted the perspective of
considering our species as simply another animal. In that
respect, we are related to mammals, primates, and the great
apes. When we look at the brain from that perspective, we
discover that all mammalian brains have much in common.
One of the striking aspects of these brain is that they allocate
parts of the brain for specific functions, such as seeing,
tasting, hearing, feeling, moving muscles, and remembering
to name a few. This is true of the brain of the cat, the
monkey, the chimpanzee and the human being. The allocation of different functions to different
parts of the brain is termed the modular principle. The modular principle differs from a
competing view of the brain which claimed that the brain was a generalized and undifferentiated
organ which absorbed knowledge like a sponge. But the modular principle is not new, going
back at least as far as the field of Phrenology in the 1830s when investigators actually mapped
out areas of the human brain and assigned functions to them. However, these investigators, had
none of the tools for investigating the functioning of the brain, like Magnetic Resonance Imaging
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(MRI), which can actually identify activity in specific areas of the brain when it is carrying out
specific functions. Thus, while phrenology was wrong about the location of specific functions of
the brain, it was in agreement with modern views of the brain with respect to the modular
hypothesis.
What is even more striking is that in mammals, the
modules for these functions are found in the same location
in every mammalian brain, this too is an observation
which current views of the brain share with phrenology.
When we compare analogous areas of the brain in a
monkey and a human we see that the functions are in
approximately the same location in both brains. For
example, figure 11 shows the midsagital motor cortex of a
monkey (based on Woosley, C.N. and P.H. Settlage
(1950)) and a human (bottom, based on Geschwind (1978)). Note the distribution of functions
(hands, feet, mouth) is the same for monkeys and humans. It is also worth noting that the areas
in humans associated with language (pharynx, tongue, jaw, gums, teeth and lips) are
considerably larger than analogous areas of the monkey brain. This observation points out
another important principle in evolution, that evolutionary change most commonly builds on, or
modifies, what exists as opposed to developing new structures altogether. In this case, as the
importance of language increased in the species, natural selection favored individuals with
greater language ability which would include larger areas devoted to language functions.
The Language Modules of the Brain
Around the turn of the last century
two physicians, first Pierre Broca and
then Carl Wernicke discovered two
distinct areas of the brain’s cerebral
cortex which carry out language
functions in the brain. These areas (see
diagram) provided some of the first
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empirical evidence for the modular hypothesis. Broca’s (1864); discoveries arose from his
treatment of war victims who had miraculously survived serious head wounds though often with
considerable disability. For example, Broca discovered that injury to the area, now known as
Broca’s area, impaired language use, a disability called aphasia. Wernicke’s area (1874) was
discovered in a like way and in so doing the discovery that the symptoms of Broca’s aphasia
were different from Wernicke’s aphasia. Strikingly, these two modules were separated from
each other and connected by a nerve bundle called the arcuate fasciculus. A third language area
of the brain was later discovered to have to do with the recognition of the written word. (The
modular hypothesis was abandoned for over half a century in favor of the mass view.)
Lateralization. In further support of the modular view, came the discovery that both Broca’s
and Wernicke’s areas tended to be located exclusively in the left hemisphere, though there is
some variation, especially in lefthanders. The location on the right hemisphere, corresponding to
Broca’s area, is typically smaller and does not deal with language.6 This phenomenon, of,
laterialization (more precisely lateral specialization), is now known to involve more than
language, and as Carter (1997:38) notes that “almost every mental function you can think of is
fully or partially lateralized.”
The two hemispheres of the cerebral cortex have distinct properties. In normal people,
the corpus callosum allows the two hemispheres of the brain to exchange information and
integrate its activity, though one hemisphere, usually the left, remains dominant. The left
hemisphere, in addition to its language functions, is also considered to be the more analytical,
more interested in detail, and more optimistic of the two, while the right hemisphere is
considered to be more intuitive, more holistic and more pessimistic. In fact, there are instances
where the two hemispheres have been seen to operate independently, for example in cases where
the corpus callosum, has been surgically severed.7 In such cases, individuals have reported cases
where their left hand (controlled by the right hemisphere) has interfered with the activities of the
right hand (controlled by the right hemisphere) which is also the language hemisphere doing the
verbal communication. In one such instance, the individual would attempt to dress herself only
6
In young children, this area in the right hemisphere can take over language functions if the left hemisphere is
severely damaged.
7
The cutting of the corpus callosum used to be used to relieve the symptoms of epilepsy.
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to discover that the left hand would grab different clothing, apparently because it preferred it to
the one chosen by the right hand. In this case, the left hand (right hemisphere) preferred brighter
and more exciting clothing. In another situation devised by researchers, the left hemisphere
reported that it wanted to be a draftsman following graduation, while the right hemisphere
reported that it wanted to become a racecar driver. Researchers also have reported a number of
other disorders relating to unbalanced functioning of the two hemispheres either due to injury to
one or the two hemispheres or the pathway (corpus callosum) between them.
The Language Modules
While Chomsky and others have metaphorically referred to the faculty of language as an
organ, one should keep in mind that it is not a coherent organ like the heart, lungs or liver, for it
cannot be traced to a single module. We have already noted that there are several areas
(modules) that have been identified with respect to language function: Broca’s area; Wernicke’s
area; and the angular gyrus. We consider them separate modules because they are located in
separate areas of the brain and because each is connected to the other through a bundle of nerves,
as for example the arcuate fasciculus which connects Broca’s and Wernicke’s areas. In
addition, we consider them different modules because they carry out different functions.
Brain Module
Impairment or Damage to Results in
Possible functions
Broca's
Area8
Can comprehend spoken speech; can produce individual
words; cannot produce function words like “of” and
“the”; cannot string words together; cannot produce
grammatical sequences.
Can speak fluently, can speak grammatical sentences, but
speech is empty of content, often cannot recall words
(anomia), use of circumlocutions, loss of understanding
speech, cannot monitor one’s own speech
Word deafness: can hear, can read and write, but cannot
recognize spoken words
Articulation of speech sounds and
production of sentences (many of the
function words appear to be part of this
area.
Recognition of speech and selection of
words for speaking.
Difficulty in recognizing distinctions among consonants
Recognition of consonants
Cannot repeat what is said
Communication between Broca’s and
Wernicke’s Areas.
Graphic identification of words
Wernicke's
Area9
Connection Between
Primary Auditory
Cortex and
Wernicke’s Area.
An Area near
Wernicke’s Area
Acurate Fasciculus
Angular
Gyrus
Can speak and understand speech, cannot recognize
written characters
Transmission of auditory information to
Wernicke’s area.
“Cookie jar ... fall over ... chair ... water ... empty.
Of a patient describing his work. “[I was] an executive of this, and the complaint was to discuss the tonations as to
what type they were ... and kept from the different tricula to get me from the attribute convenshements.” from
Carter, 1978:156-7.
8
9
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The properties of these modules are presenting a picture in which the recognition of
speech is distinct from the production of speech. It is possible for example, to have an impaired
Broca’s area rendering the articulation of speech difficult or impossible without any serious
impairment of the ability to recognize speech. We note, here, that this view is not unlike the
schematic (see front cover) offered by Saussure in his Course in General Linguistics where the
articulated speech leaves the mouth of one interlocutor and enters the ear of the other, and then to
the brain. The response begins in the brain and travels to the mouth and back to the ear of the
first speaker.
Figure 14 offers a more detailed of this process, or rather the process of what is involved
in saying the word of an image seen. First the visual impressions are converted to an image in
the visual cortex (1). Then this image is passed on to the memory association area (2) where it is
identified. This information is then passed on to Wernicke’s Area (3) where it is linked with a
sound pattern and then passed on through the acurate fasciculus to Broca’s Area where it is
articulated.
With the development of processes such as MRI, which can sample the functioning of
the brain as frequently as sixty times a minute, our understanding of the functioning of these
areas and subareas is expanding almost daily. While these discoveries support the general view
presented here, it is becoming clear that the process is much more complex involving specialized
sub-components within each area as well as other modules elsewhere in the brain.
The Evolution of the Brain
Questions
o In what fossil species is there evidence of the development of the cerebellum? Can it be
said to be a primate brain, an ape brain or a human brain?
o In endocranial casting, is there any evidence as to when specific parts of the cerebellum
developed?
Actually, the human brain consists of three brains in one. The discussion so far has
focused on the cerebral cortex which is the most recent brain to evolve. The cerebral cortex sits
on top of the mammalian brain which in turn sits on is popularly referred to as the reptilian brain
what which is the most primitive of the three. Although our understanding of the functioning of
these three brains is in its infancy, it is clear that in modern humans these three brains, while
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distinct, function together in many human tasks.
Name
Australopithecus Afarensis
Homo Habilis
Homo Erectus
Homo Sapiens
Neanderthalensis
Homo Sapiens Sapiens
Time BP
4 -3 M
3 –1 M
1 M-200k
300k-50k
Brain (in ml)
375-500
500-800
750-1250
1100-1300
Comments
50k
1200
Almost the same as Neanderthal
Evidence of bulge in Broca's area.
Evidence of Broca's area
In studying the evolution of the brain, evidence from the fossil remains of our ancestors
shows that the brain more than tripled in volume from approximately 350 ml to approximately
1300 ml over the last three million years. Importantly, this rapid (from an evolutionary
perspective) growth took place after the development of upright posture. While this increase in
size involved the cerebellum almost exclusively, there are only hints of the development of
specific parts of the cerebellum. We do know that there is evidence of a bulge in Broca’s area
which shows up in some of the skulls of Homo Habilis and further evidence of a developed
Broca’s Area in Neanderthals. This evidence suggests that selection pressures for language
abilities have been at work for at least a million years. This in turn would suggest that increasing
vocalization has been a part of our early phylogenetic development.
Comparative brain anatomy represents another approach to the study of the human brain
development. Recall the illustration comparing the distribution of sensory and motor areas in the
brains of modern humans and monkeys. We noted that while the specific functions (hands, arms,
and head were in approximately the same, figure 15 shows that the size allocated in human
brains for functions that would be involved in speech are considerably larger.
Evolution of the Vocal Tract
Current views point to the development of upright posture (some 3-4 million years ago)
as the preadaptation for the two-tube vocal tract. The term preadaptation refers to a biological
changing representing an adaptation of one sort, which enables an adaptation of another sort. In
this case, upright posture was an adaptation for something other than language, but it enabled the
development of the vocal tract. In
achieving upright posture, the skull
repositioned itself on the spine, and
this resulted a bend in the oral
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cavity creating a separate and controllable pharynx, marking the beginning of the human vocal
tract. It is important to bear in mind, that primate communication is quite rich, including facial
gestures, hand gestures, touching, hugging, grooming and vocalizations. However, when the
capacities of the vocal tract were substantially enhanced, this became a new and significant area
to expand communication. In contrast to chimpanzees, who use a wide variety of
communicative channels, facial expressions, hand gestures, touching and grooming in addition to
vocalizations, humans communicate the vast majority of their information vocally. This is
because the human vocal apparatus, when compared to that of the chimpanzee is vastly superior.
Current evidence shows that the vocal tract stopped evolving about 50,000 years
ago. This means that the selective pressures favoring the development of the vocal tract took
place before this time meaning that our ancestors were increasingly relying on the vocal tract to
communicate information. A vocal tract with two tubes of equal length cannot evolve further
because according to the source-filter theory, a further increase in either of the tubes would
produce fewer satisfactory results with the respect to vowel production.
The time period of 50,000 years ago marks the period when Homo sapiens sapiens
(modern or Cro-Magnon people) came into being and their predecessors, Homo sapiens
Neanderthalensis began to die out. The most striking physiological difference between
Neanderthals10 and Cro-Magnon is not brain size, which is about the same, but head shape. The
modern skull has a definite forehead whereas it is only modest in Neanderthals. The source-filter
hypothesis supports the view that the final step in the process of achieving a two-tube vocal tract
of equal length was to shorten the oral cavity. However, if the oral cavity is shortened, then the
entire skull must be shortened. And if it is shortened the cranial capacity will be shortened too
resulting in a smaller brain. However, if the skull increases in height, creating a forehead, the
brain size can remain the same and this is what happened according to current views.
Tool Use and Language and Human Development
Brain Growth
In addition to language, tools have been argued to be the exclusive domain of our
10
There is considerable variation between hominids of this period making classification difficult. Here, the term
“Neanderthal” refers to the classical types which are quite distinct from us (Cro-Magnon)
Cro-Magnon.
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species. Furthermore, tools appear very early in the fossil record, and may have occurred earlier.
This raises the question of the role played by tools in language and human development.
The fossil record suggests the following sequence: 1) upright posture (Australopithecus
Afarensis); 2) stone tool use and manufacture11 and some evidence of Broca’s area (homo
Habilis);12 3) vocal tract development (homo erectus). We have noted that the current evidence
shows that upright posture preceded the massive expansion of the human brain which has
increased at about the same rate since the time of Australopithecus Afarensis.
Since both tool manufacture and language development appear very early on in human
development the question naturally arises concerning their relationship.
We begin with the observation that the making of tools involves some investment in time
and energy: finding the right materials (flint) and manufacturing the tool. There comes a time
where it makes more sense to carry the tool than to manufacture it when needed. If the hands are
occupied with carrying tools, then feet would be more likely to be responsible for locomotion,
and upright posture would be a consequence. Thus, the manufacture of tools may have
contributed to upright posture.
What then of the relationship between tools and language? Secondly, several
experiments have suggested that language is not needed for the manufacture of stone tools, at
least those made by H. Habilis and H. Erectus, yet there is evidence of language evolving at that
time. But tools have an even more important relationship to language, namely that both are
manufactured (human artifacts): words are as much a human construction as are tools. We
recall, following Saussure, that words are objects consisting of a signifier and signified, and that
the signifier (token) is an object (made out of acoustic substance but nonetheless real). In this
light, tools, as objects can also be seen as signifiers to which a value could be placed making it a
sign. The question that this observation raises is the possibility that tools could have been a
preadaptation for language, marking the first semiological signs of human experience.
Note that when a person raises a spear for others to see, others look to the spear and ask
what the person has in mind. We are reacting to the person’s intent in the same way that we
11
Today, chimpanzees use tools to break nuts and to draw termites out of their nests.
We also note in passing, that our early evidence is based exclusively on the discovery of stone tools because tools
made of organic material such as wood have long since vanished.
12
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Chapter 5 Page 20
react to language. What is the person trying to convey? This line of speculation suggests that
tools could have played a crucial role in human development, leading both to upright posture and
the subsequent development of the vocal tract and to the introduction to the concept of
manufactured signs and the subsequent development of the brain over the next three million
years or so.
The Evolution of Language Structure
Under construction
Chapter Summary
What is the relationship between language and the physiology of the brain?
•
•
•
•
•
•
•
Modularity areas (Broca's and Wernicke's) are equally important. Both are located in likely areas.
Broca's (near motor area) (articulatory, syntactic function)
Wernicke's in the memory area (lexical function)
Evidence suggests that the brain, like the vocal tract has evolved in such a way that human language is
facilitated.
There seems to be come correlation between physiological structure and language structure.
Broca's: syntax and articulation (assembly of language): Wernicke's area: lexical storage and association.
However, this correlation simply states that there is a physiological correlation. One could make even stronger
claims: e.g., the innateness hypothesis.
Questions for Study and Review
1. Sometimes human evolution is mistakenly characterized by saying that human beings evolved from monkeys.
Can you identify the error in this statement?
2. Although we noted that evolution does not have a direction, can you offer an explanation as to why ears
developed independently in insects and in mammals?
3. We noted that the term developed is a better term than discovered or invented or to describe the emergence of
writing system. Explain this statement in your own words.
4. In what way does the evolution of writing systems illustrate the principles of evolution? How would you
characterize the development of the alphabet?
5. What kind of writing system is associated with the following languages? Russian, Korean, Hindi, Mayan and
Spanish.
6. Goody’s argument about the consequences of literacy provides an illustration of the concept of preadaptation.
Can you explain why?
7. Why are vowels so central to the evolution of the vocal tract?
8. The terms harmonic and formant are easily confused. Can you explain the difference?
9. My high school science teacher once illustrated a property of acoustics by inhaling helium from a balloon.
When he spoke, his voice was much higher than normal, because of the properties of helium. Can you explain
why?
10.
According to the sound-filter theory, why are two-tubes necessary for the production of vowels?
11.
In what way can the lungs, tongue, lips, larynx, and pharynx be termed “organs of speech?”
12.
One of the consequences of the evolution of the vocal tract is a far less functional epiglottis in adult
humans. This increases the risk of choking and occasionally results in death. How can this development
be explained in evolutionary terms?
13.
In what sense is the outmoded field of phrenology an illustration of the modular hypothesis?
14.
What evolutionary principles does the evolution of Broca’s area illustrate?
The Consequences of Language: How did people get language?
15.
16.
Chapter 5 Page 21
Linguists have assumed that humans use the same grammar to speak and to comprehend. Is this supported
by the evidence from aphasia? Why or why not?
How is upright posture a preadaptation for language development?
Suggestions for Further Reading
Evolution of Writing
o
Schmandt-Besserat. The earliest precursor to writing. Human Communication. W. S_Y. Wang (ed.). W.H.
Freeman and Company. 1981:63_71
o
Goody and Watt. The Consequences of Literacy. Language and Social Context. P. Giglioli (ed.).
Middlesex, U.K.: Penguin Books. 1979:311_357.
Street, Brian. Literacy in theory and practice. Cambridge: Cambridge University Press. 1984.
Street, Brian. Cross-cultural approaches to literacy, Brian Street (editor). Cambridge: Cambridge
University Press. 1993 xii, 321.
o
o
The Vocal Tract.
o
Miller. The source filter theory. Language and Speech. 1981. San Francisco, W.H. Freeman & Co. 37_48.
The Brain
o
o
Jackendoff, R. 1994. Patterns of the Mind. New York: Basic Books.
Geschwind, Norman. Specializations of the Human Brain. Human Communication. San Francisco: W.H.
Freeman & Co. 1978:121-31
Glossary
Australopithecus Afarensis
Cro-Magnon
Preadaptation
Homo Habilis
Corpus callosum
Laterialization
Wernicke’s area
Arcuate fasciculus
Broca’s area
Carl Wernicke
Pierre Broca
The Faculty of Language
Filter
Herz
Selection
Mutation
Phylogenetic
To Do
Brain Growth