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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. Muelleri x H. Lar:

H. Lar

H. Lar x H. Muelleri:

H. Muelleri:

Hybrid Songs

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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?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.

--Terence Deacon, “The Symbolic Species”

Are humans monogamous?

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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 learningin 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 non-cooperation; 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. Don’t rock the boat: if RRR then C

2. Be provocable: if RRS then D

3. Accept apologies: if TSR then C

4. Forget: if SRR then C

5. 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