Transcript Document

Perspectives on Human
Linguistic Variation
College 002 -- Spring Term 2002
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Variation across human
languages
• Navajo vs. English
– Vocabulary, morphology, grammar
– Culture
• Navajo Code Talkers
– USMC WWII battlefield encryption
– Small dictionary + general translation
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Variation within English
• Read the first few paragraphs of this link, and
listen to the 11 examples of American
dialects.
Ask yourself to identify:
–
–
–
–
sex
age
region
class
• How accurate do you think you are?
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Human linguistic variation in biological
perspective
• Universality and species specificity
– like Gibbons
• Constrained variation
– like Humpbacked Whales
and Zebra Finches
• Structural adaptation
– like siamang gular sacs
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Gibbons
• Arboreal apes
– tropical rain forests of southeast asia
– 12 species in four (sub-)genera
• subgenera are somewhat more different
than humans and chimps
– brachiation
– monogamy
• like 3% of mammal species
• 90% of bird species
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Gibbons and us:
Primate Phylogeny
Among the apes, only gibbons and humans have pair bonding.
Also, only gibbons and humans sing…
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Gibbon duetting
All species of gibbons are known to produce elaborate,
species-specific and sex-specific patterns of
vocalisation often referred to as "songs" (Haimoff, 1984;
Marshall & Marshall, 1976). Songs are loud and
complex and are mainly uttered at specifically
established times of day. In most species, mated pairs
may characteristically combine their songs in a relatively
rigid pattern to produce coordinated duet songs. Several
functions have been attributed to gibbon songs, most of
which emphasise a role in territorial advertisement,
mate attraction and maintenance of pair and family
bonds (Geissmann, 1999; Geissmann & Orgeldinger in
press; Haimoff, 1984; Leighton, 1987).
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The female “great call”
The most prominent song contribution of female gibbons
consists of a loud, stereotyped phrase, the great call.
Depending on species, great calls typically comprise
between 6-100 notes, have a duration of 6-30 s. The
shape of individual great call notes and the intervals
between the notes follow a species-specific pattern.
. A female song bout is usually introduced by a variable but
simple series of notes termed the introductory sequence;
it is produced only once in a song bout. Thereafter, great
calls are produced with an interval of about 2 min. In the
intervals, [are] so-called interlude sequences consisting
of shorter, more variable phrases … The typical female
song bout hence follows the sequential course
ABCBCBCBC…,
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Male duet contributions
As a rule, adult males do not produce great calls, but "male short
phrases" only. Whereas female great calls remain essentially
unchanged throughout a song bout, males gradually build up
their phrases, beginning with single, simple notes. As less
simple notes are introduced, these notes are combined to
increasingly complex phrases, reaching the fully developed form
only after several minutes of singing …
During duet songs, mated males and females combine their song
contributions to produce complex, but relatively stereotyped
vocal interactions… Both pair partners contribute to an
introductory sequence at the beginning of the song bout (A).
Thereafter, interlude sequences (B) and great call sequences
(C) are produced in successive alternation…
During great call sequences the male becomes silent and does not
resume calling until near or shortly after the end of the female's
great call, when he will produce a coda.
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Gibbon song samples
• Hylobates Lar
– white-handed gibbon
– Female “great call”
with male “coda”
• Hylobates Muelleri
– gray gibbon
– Female “great call”
with male “coda”
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H. Lar
Hybrid Songs
H. Muelleri x H. Lar:
H. Lar x H. Muelleri:
H. Muelleri:
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Phylogeny of singing in primates
Singing is rare in mammals. It occurs in members of 26 species in four primate genera:
Indri, Tarsius, Callicebus, Hylobates. These are 11% of primate species and 4% of
primate genera. Since the four singing genera are widely separated, they are thought to
have evolved singing independently.
In all singing primates, both males and females sing, and duetting usually if not always
occurs. All singing primates are monogamous (with the possible exception of humans).
Most bird species sing; often bird song is mostly male; duetting bird species are also
usually monogamous.
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Are humans monogamous?
Are humans monogamous?
In most mammalian species, sexual access is either determined
by rank… and results in polygyny; or else … two individuals
become “attached” to one another and then isolate themselves
from other members of their species…
[In humans] what is common is… cooperative, mixed-sex
social groups, with significant male care and provisioning of
offspring, and relatively stable patterns of reproductive
exclusion, mostly in the form of monogamous relationships.
Reproductive pairing is not found in exactly this pattern in any
other species.
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--Terence Deacon, “The Symbolic Species”
Gular sac
Some gibbons have developed a large
“gular sac” apparently involved with
breath control and/or resonance.
Gular sac size and song complexity
seem to correlate across species.
Symphalangus syndactylus
(siamang):
“the [siamang] duet is probably the
most complicated opus sung by a
land vertebrate other than man…”
--Marshall and Sugardjito (1986)
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Zebra Finch
(Taeniopygia guttata)
• Small songbird (Australia and Timor)
• Highly social (colonies of 20-1000)
• Pair bonding (with frequent “cheating”)
– Male display, females choose
– bond marked by “clumping” and preening
• Males sing, females do not
– part of sexual and territorial displays
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Typical Zebra Finch song
• Not intrinsically pleasing to most humans
• nasal quality, repetitive rhythm
• Production requires difficult motor control and
large expenditure of energy
• Female Zebra Finches (and competing males)
are wiling to be impressed
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Song learning
in Zebra Finches and other oscines
• Song patterns are species-specific
• However, exposure to adult patterns is necessary for
normal sing development
– deafened birds develop highly degraded song
– birds reared without adult male models
develop degraded but species-typical songs
• Sensitive/critical period for exposure
– 20-35 days after hatching
• Active song develops later
– 60-90 days after hatching
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Why learned songs?
• Some sub-oscine species have completely
programmed song
– deafened or isolated birds sing normally
• Suggested advantages of learned song:
– more complex or varied song via cultural rather than genetic
development
• females prefer constrained novelty
• promotes exogamy in large colonies
– intra-species varients of song, called dialects, may serve to
segregate populations of the same species
• promotes endogamy in microhabitats
– more rapid adaptation of the song to different acoustic
environments
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Humpback Whale Songs
• Samples:
• Variation and change:
– At any one time, all whales sing similar
songs
– Over time, songs change rapidly
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How do behaviors evolve?
• Mapping from genes to behaviors is
almost completely mysterious
• The mapping from genes to morphology
is not much better understood
• However, the principles of evolution are
clear, even where the detailed
mechanisms are not
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Example:
Strategies for the “Iterated Prisoner’s Dilemma”
• The “prisoner’s dilemma” paradox
• The “iterated prisoner’s dilemma”
– Proposed in 1984 by Robert Axelrod
• The IPD tournaments
• Genetic algorithms
• Applications of GA to the IPD
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The “prisoner’s dilemma” paradox
Origin: situation of captured thieves
– if everybody keeps silent, all go free
– if one confesses
• (s)he gets a reward
• everyone else gets a heavy sentence
– if everyone confesses
• everyone gets a moderate sentence
If you analyze the options objectively, your best bet is
to confess. But if everyone confesses, everyone is
worse off than if everyone kept silent.
Generically: total cooperation is better than total noncooperation; but any individual can then better his or
her situation by “defecting”.
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PD payoff matrix
(payoff to me)
Temptation >> Reward >> Punishment >> Sucker’s payoff
[Also: (Temptation + Sucker)/2 <= Reward]
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Consider the options…
• If you defect
– if I cooperate I pay $100
– if I defect I pay $10
– so my best bet is to defect…
• If you cooperate
– if I cooperate I get $300
– if I defect I get $500
– so my best bet is to defect…
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PD without money or cops:
the “furry critter’s dilemma”
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Conclusion: nice guys finish last
• PD arguments were used to “prove” that
cooperation could never be an evolutionarily
stable strategy, except perhaps among kin
• “Every man for himself, and the devil take the
hindmost…”
• A depressing conclusion in the context of the
cold war, where nuclear standoff looks very
much like a PD situation.
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Axelrod’s innovation
(1984)
• Treat PD as a game with repeating turns
– Endless, or at least players don’t know when the
end will come
• Add up the scores across turns
• Play different strategies against one another
– Human game-playing
– Better, let the computer do it
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Payoff matrix for Axelrod’s game
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First try
• Axelrod advertised for strategies
– 14 were submitted, some very complicated
– Axelrod added one: Random
• Run a tournament: every strategy plays against every other
strategy 200 times
• The winner:
– “Tit for tat” (submitted by Anatol Rapoport)
– “Cooperate with strangers, and otherwise do whatever the opponent
did last time around”
• If we define a “nice” strategy as one that is never the first to
defect, then the 8 top scoring strategies (out of 15) were “nice”.
• “Forgiving” strategies do better than those that bear grudges
– in fact, “tit for two tats” would have won if it had been entered
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Second try
• Analysis of first tournament was published
• Second tournament was opened to any new
entrants
– 62 entrants this time
– number of rounds was left open
• Result: “tit for tat” wins again
– including against “tit for two tats”
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More results
• Many other analyses and competitions
• Two attempts at evolutionary simulations
– (1) Evolutionary competition among fixed set of 63
strategies
• “tit for tat” won 5 out of 6 rounds
• A similar “nice, forgiving” strategy won the 6th
• However, no such strategy is “evolutionarily stable”, in
the sense that a uniform population can always be
successfully invaded by an alternative.
– (2) “Genetic algorithm” to evolve new strategies
and let them compete
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Evolving PD strategies
• Strategies as pseudochromosomes
– 4 possible outcomes at each stage of the game
– 4 x 4 x 4 = 64 possible 3-move “histories”
– To determine how to act in each of these 64 cases
requires 64 specification of “C” (cooperate) or “D”
(defect)
– Thus a PD “gene” is a string of 64 C’s or D’s
– Add 6 more to cover the first 3 moves
– Total of 70 letters make up a pseudochromosome
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Mutations and mating
• Mutation: just change one of the 70
letters from C to D or from D to C, with
some small probability
• Mating: combine two “genotypes” by
selecting a random crossover point
– crossover point of 9 combines 1-9 from
one parent with 10-70 from the other, and
vice versa
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Natural selection
• Run a mini-tournament and score each
genotype
• Mate genotypes (with random
mutations) to produce offspring in
proportion to their score on the previous
round of the tournament
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Results: overall population fitness improves
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Gene pool analysis
•
Five “alleles” evolved in the vast majority of
individuals:
1.
2.
3.
4.
5.
–
Don’t rock the boat: if RRR then C
Be provocable: if RRS then D
Accept apologies: if TSR then C
Forget: if SRR then C
Accept a rut: if PPP then D
Most of the resulting “individuals”
beat tit-for-tat
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Back to language
• Natural selection vs. sexual selection
– differential survival (and thus reproduction)
vs. differential reproduction, period.
• Sexual selection
– Non- (or dys-) functional appearance, sound
– Social and mating behavior
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