Transcript Language evolution

Language evolution
• Features of human language
• Evidence for a universal grammar
– Language development
– Language disorders
– Pidgeons and creoles
• Animal language experiments
• Fossil evidence
• ESS approaches to language evolution
What is language for?
• Permits us to form internal representations
of objects in our minds
• Allows us to convey what we are thinking
• Provides labels for categories of objects, i.e.
dangerous vs nondangerous, which form
hierarchies
Words form hierarchies
Sentences have hierarchical
structure
“ This is the man all tattered and torn, who
loved the maiden all forlorn, who milked
the cow with the crumpled horn, that kicked
the dog that chased the cat that killed the rat
that ate the malt that lay in the house that
Jack built”
Noun phrase structure
Universal grammar
• No more than two branches spring from the
same node, but phrases can be stacked
together like Chinese boxes
• Subject-verb phrase
• Verbs have argument structure, i.e. “John
sleeps”, “John hit Mary”, ‘John gave Mary
a present”
• Meaning depends on order, “John is
hungry” ≠ “Is John hungry?”
Consequences of grammar
• Using a few rules, can produce an infinite
number of sentences. All languages utilize
a structurally similar grammar.
• Words must be learned and associated with
objects, actions and relationships. The list
of words used in a language is the lexicon.
Evidence for universal grammar
• Children follow consistent patterns of
language development independent of culture
• Language disorders disrupt grammar, but not
overall mental competency
• Caspar Hauser children and apes exhibit
protolanguage
• Creole languages have evolved in single
generations from pidgeons in many parts of
the world
Infant vocal development
Word development follows
object manipulation patterns
• Reduplicated consonant-vowel
syllables: dada, mama
• Single consonant combined with
single vowel: na (for no)
• Single consonant combined with
different vowels: baby
• Initial consonant varies, but vowel
remains constant: kye-bye (car byebye)
• Syllabic subassemblies are
combined: ball
Syntax ontogeny
Grammar also follows ontogenetic
pattern of object manipulation
Language aphasias
Disrupts grammar structure,
but sentences are coherent
Sentences are grammatically
correct, but meaningless
Both forms disrupt ability to
reproduce drawings
Protolanguage
• Big train; Red Book
• Adam checker;
Mommy lunch
• Walk street; go store
• Adam put; Eve read.
• Put book; Hit ball.
2-year old child
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Drink red; Comb black.
Clothes Mrs G; You hat.
Go in; Look out.
Roger ticket; You drink.
Tickle Washoe; Open
blanket.
Trained chimpanzee
Animal language studies
Caspar Hauser children
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Want milk,
Mike paint.
Applesauce buy store
At school wash face
Very sad, climb
mountain
• I want Curtiss play
piano
• 13 year old girl who
was imprisoned at 18
months
• Never learned to speak
• Normal ability to form
concepts
Pidgeons and Creoles
• Pidgeon languages are formed by people
who do not share a language, e.g. slaves in
island colonies, “Forman, who carry? Carry
all, cut all” or traders.
• Children of pidgeon-speaking parents form
Creole languages, which have complete
grammatical structure, in 1 generation.
These have developed in many parts of the
world with similar grammars
When did language appear in
hominid evolution
Competitive hominds: Koobi Fora
Australopithecus boisei
Homo ergaster
Paleolithic technology
Oldowan, 2.4-1.5 MYA
Acheulean, 1.4-0.2 MYA
Cave and rock paintings
40,000 bp, Kakadu NP, Australia
27,000 bp, Cosquer, France
Cave paintings
17,000 bp, Lascaux, France
Neocortex size and group size in primates
Grooming time increases with group size
Tribal group sizes
Predicted grooming times for hominoids
Global linguistic diversity
Human language diversity
• Cooperative trading requires a common
language
• Conformity to a language could be used as
an honest signal or group affiliation
• Expect linguistic uniformity when social
networks are large, and distinct languages
when networks are small and self-sustaining
Latitudinal patterns of language diversity
Language diversity and growing season
ESS approach to word evolution
• Relying on a different sound for every
object requires multiple sounds which
eventually become hard to distinguish
• Increase understanding by limiting number
of sounds and stringing them into
sequences, i.e. words.
• Expect words to evolve when there are a
large number of things to name
ESS approach to syntax
• For a word to survive in a community, it must be
used enough to be heard and remembered.
• Memory is constraining if all concepts require
unique words
• Can increase information using syntax
• In a combinatorial world, the number of words a
syntactic communicator needs to know is the sum
of objects and actions, whereas a nonsyntactic
communicator needs to know the product.
Syntax evolution: the problem
Syntax evolution: the answer
ESS approach to universal grammar
• Considers fitness advantage when
alternative grammars are in competition
• Acquisition of correct grammar requires
learning from sample sentences
• Optimal learning period occurs at
intermediate number of sentences to insure
coherency
• Rule-based grammars are more efficient
than list-based grammars
Evolution of universal grammar
Language evolution references
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