the gestural origins of language - uqam€¦ · the gestural origins of language. or, how language...

Michael Corballis

University of Auckland

The gestural origins of language

Or, how language went fromhand to mouth

Pedigree

Cresollius (1620), Mandeville (1728), Condillac (1746), Rousseau

(1782), Tylor (1868, 1871), Morgan (1877), Wallace (1881),

Romanes (1888), Wundt (1912), Paget (1944), Johanneson (1949,

1950), Hewes (1973), Wescott (1974), Critchley (1975), Steklis &

Harnad (1976), Engelfield (1977), Kimura (1979), Armstrong,

Stokoe & Wilcox (1991), Kendon (1991), Corballis (1991, 1999),

Donald (1991), Allott (1994), Givon (1995), Rizzolatti & Arbib

(1998), Skoyles (1998), Armstrong (1999), Goldin-Meadow &

McNeill (1999), Wells (1999), Place (2000), Arbib (2005), Rizzolatti

& Sinigaglia (2006), Armstrong & Wilcox (2007), Tomasello

(2008)—and more

“What’s the one obvious thing we humans do that [chimps]

don’t do? Chimps can learn sign language, but in the wild, so

far as we know, they are unable to communicate about

things that aren’t present. They can’t teach what happened

100 years ago, except by showing fear in certain places.

They certainly can’t plan for five years ahead. If they could,

they could communicate with each other about what compels

them to indulge in their dramatic displays. To me, it is a

sense of wonder and awe that we share with them. When we

had those feelings, and evolved the ability to talk about

them, we were able to create the early religions”

In conversation with Freddy Gray, on p. 13 of The Spectator of 10 April, 2010.

Jane Goodall on chimps

Or Robert Browning …

! “He said ‘What’s time? Now is for dogs and

apes! Man has forever’”

--from A Grammarian’s Funeral (1855)

Six reasons to believe that languageevolved from manual gestures

"# The hands as a “natural” communication system

$# In great apes, gesture is closer to language than is

vocal communication

%# “Mirror neurons” in primates form a natural platform

for language evolution

&# Signed languages are true languages

'# Handedness and cerebral asymmetry for language

are correlated, suggesting common influence

(# Development of speech depends on a gestural

scaffold

1. Why manualgestures have thedesired properties

The 4D World

! We live in 4D space-time

! Voice conveys information in 1D only

! Gestures convey information in 4D

! Allows iconic representation

! Vision is our dominant mode

! The hands and arms provide the “natural”way to communicate about events in theworld

Visuo-manual action

! Long history in primates

! Arboreal adaptations

! Adaptation of hand for manipulative

activities: fruit-plucking, tool use, grooming,

catching insects, …

! 3D colour vision

! Intentional behaviour

A pitcher is worth a thousand words

2. Great ape gesturesare more language-like than are their

vocalizations

Jane Goodall: Chimp unable to suppress

pant-hoot on discovery of cache of bananas

“The production of sound in the absence

of the appropriate emotional state seems

to be an almost impossible task for a

chimpanzee.”

--The Chimpanzees of Gombe (1986, p. 125)

LACK OF VOLUNTARY VOCAL

CONTROL IN CHIMPS

Flexibility of manual and vocalgestures in great apes

! Manual gestures much

less tied to “typical”

contexts than

facial/vocal gestures in

chimps and bonobos

Pollick, A. S. & de Waal, F.B.M. (2007). PNAS, 104, 8184-8189

Flexibility of manual and vocalgestures in great apes

! Much lower correlations

between groups for manual

than for facial/vocal gesture

Pollick, A. S. & de Waal, F.B.M., (2007). PNAS, 104, 8184-8189

LIMBIC SYSTEM NEOCORTICAL SYSTEM

Ploog, D. (2002). In T. J. Crow (Ed.) The speciation of modern Homo Sapiens. OUP

Two systems of vocal control

Evolved in mammals,

with increasingly

differentiated control

over hands, fingers,

articulators, & vocal folds

Anterior cingulate

Cerebral peduncle

Peri-acqueductal grey

Motor strip

Pyramidal tract

Nucleus ambiguous

Some chimp gestures

Arm-on Arm-raise Back-off

Ball-offer Belly-offer Direct-hand

Foot-stomp Genital-offer Ground-slap

Hand-beg Hand-clap Head-bob

Head-shake Lead Leg-offer

Lip-lock Look-back Point

Poke-at Push-object Raise-object

Reach Rub-chin Shake-object

Spit-at Swagger Throw-stuff

Touch-side Wave-object Wrist-offer

—from Tomasello, Call, Warren, Frost, Carpenter, and Nagell (1997)

Teaching “language” to great apes

! No success in teaching apes to talk

! Moderate success in teaching forms of

signed language

! Washoe

! Kanzi

! Koko

Savage-Rumbaugh, S., Shanker, S.G. and Taylor, T.J. (1998). Apes,

language, and the human mind. New York: Oxford University Press.

Savage-Rumbaugh, S., Wamba, K., Wamba, P., and Wamba, N. (2007).

Applied Animal Science, 10, 7-19.

Kanzi (a bonobo) has quiteextensive visual language

3. Mirror neurons

Mirror neurons

! First discovered in Area F5 in the monkey

! Fire when the animal makes a grasping movement, and also when itobserves the same movement made by another

! Maps observation onto execution

Variety of mirror neurons

! Some respond to relatively precise

correspondence between actual

and observed movements (e.g.,

precision grip)

! Others respond if the movements

are different but the goal is the

same (e.g., grasping with normal or

reversed pliers)

“Mirror neurons will do for psychology what DNA has done for biology”!V.S. Ramachandran

Object-related activity

! In monkey,mirror neuronresponds only ifthere’s an actualobject …

! …even if it’shidden but themonkey knowsit’s there

Object-related action is termed transitive

Transitive and intransitive action inhumans

! Mu rhythmsuppression indexesmirror neuronresponse

! Suppressiongreatest for grip(transitive)

! Less for flat handand grip form(intransitive) but stillsignificant

Muthukumaraswamy SD et al. (2004) Cognitive Brain Research, 19, 195-201

Flat hand Grip form Grip

Homologous areas in monkey andhuman brain

! Primary motor

cortex

! Premotor

cortex

! Mirror neuron

area. In

humans this is

also Broca’s

area

The extended mirror system inprimates

From Rizzolatti G, Sinigaglia C. (2010) Nature Reviews Neuroscience, 11, 264-274

Parietal mirror

neurons

STS neurons

respond to

perception of

biological motion,

but not to actionFrontal mirror neurons

Essential overlap between mirrorsystem and language system

Mirror system in monkeys Language network in human

Language is incorporated in the human mirror system,

predominantly in the left hemisphere

Mirror neurons in primates respond toaction-related sound, but not to primatecalls

Note mirror neurons don’t really mirror; they map visual or auditory

stimuli onto the actions that produce them

Kohler, E., et al. (2002). Science, 297, 846-848.

Changes required for language

! Mirror system responds to intransitive as well astransitive actions. This allows the system tomove beyond understanding of object-graspingto use of gesture in symbolic communication(e.g., mime, and eventually speech)

! More complex programming to supportgrammar? (Arbib, 2005)

! … and for speech, vocalization was incorporated(and biased the system to the left hemisphere)

Arbib, M.A. (2005). Behavioral & Brain Sciences, 28, 105-168.

4. Signed languages

Properties of signed languages

! Have all the linguistic sophistication ofspoken language

! Arise spontaneously in deaf communities

! Emerge as pantomime but becomeincreasingly conventionalized andgrammaticalized

! Depend on same brain areas as spokenlanguages (“sign language aphasia”)

Bellugi, U., & Klima, E.S. (1976) Annals of NYAS, 280,, 14-538

Signs are not mutually transparentbetween different sign languages

Different signs

for “tree”

5. Handedness andcerebral asymmetry

The right-shift theory

! ~88% of human population are right-

handed

! ~ 91% of human population are left-brain-

dominant for language (spoken or signed)

! These asymmetries are correlated

! Both influenced by the same “right-shift”

gene (Annett, 2002)

Annett, M. (2002). Handedness and brain asymmetry: The right shift theory. Psychology Press.

How two alleles of the RS geneinfluence handedness

I I I I I I l

-2 -1 0 1 2 3

RS--

RS+-

RS++

R-L (in standard deviations)

Problem

! How to explain the higher incidence

of left-cerebral language dominance

than of right-handedness?

Annett’s “right shift” theory

Left-handed Right-handed

Right Left Hemisphere dominant for language

RS+

RS-

RS++

RS+-

RS--

Dominant-recessive

influence in

cerebral asymmetry

Additive influence

in handedness

An alternative version

Left-handed Right-handed

Right Left Hemisphere dominant for language

RS++RS--

RS++

RS+-

RS--

Additive model for

both cerebral

asymmetry and

handedness, with

reduced environ-

mental influence

for cerebral

asymmetry

RS+-

6. The gesturalscaffold for speech

development

Volterra, V., Caselli, M.C., Capirci,O., Pizzuto, E. (2005). Gesture and the emergence and development of language . In M. Tomasello and

D. Slobin, (Eds.) Beyond Nature-Nurture. Essays in Honor of Elizabeth Bates. (pp. 3-40) Mahwah, N.J.: Lawrence Erlbaum Associates.

Em

erg

ence

of

language

Emergence ofintentional

communication

Manual components(gestures)

Vocal components(words)

Bimodal period

Two-wordstage

9 ……………………… 14 ……………..….. 24Months

Em

erg

ence

of

language

Emergence ofintentional

communication

Manual components(gestures)

Vocal components(words)

Bimodal period

Two-wordstage

9 ……………………… 14 ……………..….. 24Months

How did the switchoccur?

Neuron discharge

during grasping

with the mouth.

Neuron discharge

during grasping with

the contralateralhand

Neuron discharge

during grasping

with the ipsilateral

hand

Rizzolatti, G., et al. (1988) Exp. Brain Res. 71, 491-507.

Recordings from area F5 in

the monkey brain

Link between hand and mouth inprimates

Gentilucci, M., et al. (2004). European Journal of Neuroscience, 19, 190-202.

Also in humans: Vocalization changesdepending on action

A Subject says “ba”

B Subject vocalizes

nonlinguistic sound

C Observation of

action

D Pantomime of

action

E Nonbiological arm

cherry

apple

*

* *

Subjects say “ba” while watching a persongrasping cherry or apple

Gentilucci, M., et al. (2004). Neuropsychologia 42, 1554-1567.

C = children

A = adults

The switch was gradual

! Probably from hands to face to vocal tract

! Speech is facial gesture half-swallowed, butwith vocal accompaniment

! Vocalization allows internal gestures(tongue, velum, larynx) to be accessible

! Control of the vocalization was the last step,involving changes to vocal tract, breathing,tongue control, and control of the larynx

Speech itself is a gestural system, notan acoustic one

! Mirror system already preadapted for either

visual or acoustic input

! These are mapped onto gestures

! Language is an embodied system—we

communicate using our bodies

Motor theory of speech perception

! Lack of invariance in acoustic signal

! Invariance lies in production (or gesture)

! Hence all language, spoken or signed (or both), maps onto gestures

Articulatory phonology

! Speech conceived as gestures of the lips,

the velum, the larynx, and the blade, body,

and root of the tongue

! Perception of speech involves recovery of

gestures, not acoustic analysis

! These gestures are partly visible

(lipreading, McGurk effect, …)

Why the switch?

Speech frees the hands

! Allows development of manufacture

! Also allows the development of pedagogy, sothat manual activities (e.g., making and usingtools, cooking lessons, etc) can bedemonstrated and verbally described at thesame time.

! Speech is much less demanding of energyresources

! Speech is miniaturization

• Does not work in the dark, or when obstacles intervene.

• “[African languages are not elaborate enough] to enable

a native to state his exact thought. Some of them are very

dependent upon gesture. When I was with the Fans they

frequently said "We will go to the fire so that we can see

what they say", when any question had to be decided

after dark, and the inhabitants of Fernando Po, the Bubis,

are quite unable to converse with each other unless they

have sufficient light to see the accompanying gestures of

the conversation.” —Mary Kingsley, Travels in West Africa, 1897,

reprinted 1965, p.504

Gesture needs light

When did the switchoccur ?

Speech may have become dominantwith H. sapiens

! This could explain the rise of “modernity”

from around 90,000 years ago

! More sophisticated manufacture

! Cave art, sculpture, bodily embellishment

! Burial rites

! FOXP2 mutation

Changes for speech occurred late inevolution of Homo

! Lowering of larynx

! Lengthening of

tongue and neck

! Flattening of face

! These changes

not complete even

in Neanderthal,

30,000 years

ago?

Orangutan Chimp Human

Human Neanderthal

An extreme conclusion?

! “… fully human speech anatomy first

appears in the fossil record in the Upper

Paleolithic (about 50,000 years ago) and is

absent in both Neanderthals and earlier

humans” (Lieberman, 2007, p. 39)

—Lieberman, P. (2007) The evolution of

human speech. Current Anthropology, 48, 39-46

The FOXP2 gene

! KE family: deficits in speech due to mutation on

the FOXP2 gene on chromosome 7

! The primary deficit is oro-facial movement*

! Affected members of the KE family don’t show

activation of Broca’s area when generating verbs

! FOXP2 gene responsible for introducing articulate

vocalization to the mirror system?

*Watkins, K.E., et al. (2002). Brain, 125, 452-464.

FOXP2 and the MirrorSystem

! Unaffected KE members show activation ofBroca’s area when generating verbs

! Affected members show bilateral activationexcluding Broca’s area

! Could FOXP2 have assimilatedorofacial/vocal control into Broca’s area,and the mirror system?

Liégeois, F. et al., Nature Neuroscience, 2002, 11, 1230-1237

Evolution of the FOXP2 gene

! FOXP2 underwent 2 mutations in hominins afterthe split from the apes

! The more recent occurred not later than “the timesince the onset of human population growth, some10,000 to 100,000 years ago. … This is compatiblewith a model in which the expansion of modernhumans was driven by the appearance of a more-proficient spoken language” (Enard, W. et al. (2002)Nature, 418, 871)

! Another molecular analysis suggests mutation was42,000 years ago (Coop, G., et al. (2008). Molecular Biology andEvolution, 25, 1257-1259.)

BUT

! Recent evidence that the FOXP2 mutation

was present in the DNA of a 45,000-year-

old Neanderthal*

! This implies that the mutation may go back

400,000-5000,000 years, to the common

ancestor of humans and Neanderthals!

*Krause, J., et al. (2007). Current Biology, 17, 1908-1912.

BUT

! Evidence now suggests some mating

(DNA exchange) between

Neanderthals and non-African

humans from 50,000 to 80,000 years

ago (Green et al. (2010) Science 328, 710-

722)

! The FOXP2 story is not yet over

The power of speech

! Responsible for the “evolutionary

explosion” and development of modernity?

! Also responsible for the dominance of

humans over other hominins, and eventual

extinction of them all?

! Are other “revolutions” also dependent on

changes in communications systems

(writing, internet, cellphones)?

And we still gesture as we speak

‘And do you, Stephanie, promise to love, honor, and “obey”?’