1 LING001 Evolution and Language 4-27-2009. 2 Evolution and Language “Nothing in biology makes sense except in the light of evolution”. Theodosius Dobzhansky.

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LING001

Evolution and Language4-27-2009

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Evolution and Language

• “Nothing in biology makes sense except in the light of evolution”. Theodosius Dobzhansky (1973)

• The uniqueness of human language in the biological world has driven people to “make sense” of it in the light of evolution.

• But it is important to distinguish mere “stories” from testable scientific theories

• Today:

• basic structure of Natural Selection and the difficulties with which it is applied to language and cognition (Lewontin)

• some suggestions about the evolution of language

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Angry Dick

• Richard Lewontin (b. 1929): perhaps the greatest living evolutionary biologist, also prominent social commentator

• Outlines the structure of the argument for Natural Selection and dismisses existing accounts of evolution of language as story telling

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Three Components of Natural Selection

• Variation: individuals must be different (no variation, no evolution)

• Heredity: differences must be passed down to descendants

• Selection: differential reproduction and survival due to variation

• The fallacy of the role of skin cancer in the evolution of skin colors

• Fitness is not constant: Bad eyesight is a good reason to avoid the draft

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Natural Selection in Real World

• Natural Selection only increases the probability of passing down the gene but doesn’t guarantee it: like a coin toss

• N.S. can boost the chance of getting tails from 0.5 to 0.51 (0.01 advantage is considered large in nature)

• If the population is very large, tails will make up close to 51% of the population in one generation, and more next, and will gradually take over

• But if the population is small, you may not have get more tails in next generation even if it’s more likely to draw tails

• Draw 10 balls: 60% of drawing red, 40% of drawing green

• we may end up with a 6-4 split, but also 5-5, 2-8, even 0-10

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Natural Selection in Real World

• For human evolution, it is generally held that while in Africa, and when our ancestors marched out of Africa, the population size was quite small

• this makes the effect of sampling a lot more dramatic

• as a result of this and other factors, in human evolutionary genetics, the default hypothesis of observing change is to assume that it is NOT caused by Natural Selection

• Which is why no serious biologists participate in the story telling of the evolution of language and cognition: it’s almost exclusively the game of psychologists, philosophers, ... and linguists!

http://news.nationalgeographic.com/news/2008/04/080424-humans-extinct.html

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Stories• It’s possible to simply tell plausible stories about biological properties of organisms.

• In the case of language, there are many such stories; language is required for communication, hunting, evolved because of gossip

• :This ‘story-telling’ can involve more or less plausible parts; but ultimately we’re interested in theories that can be tested, and that’s where most of Lewontin’s critique is directed.No one doubts language did

evolve by biological mechanisms

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A “just so” story

• Pinker & Bloom (1990: cited in Lewontin article)

• Because language is complex (any questions?), it must be the product of Natural Selection

• Because Natural Selection has produced many complex things though complexity is also the argument used by creationists as evidence of a Designer

• Much of evolutionary psychology has held Natural Selection to be the force that created cognitive systems

• “God gene”, “cheater detector gene”, etc., each with a Natural Selection story that “makes sense”

• But gene-trait mapping is not unique

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Difficulties with Evolution of Language

• Language doesn’t leave fossils

• We have no “close” relatives: chimps diverged from us about 5-7 million years ago

• no time to evolve every component of language individually, contrary to Pinker & Bloom

• The measurement of cognitive abilities is itself very challenging

• the Bell curve and the IQ test controversy

• Not clear where to find genetically based variation

• Not clear how variation translates into selectional advantage

• the first caveman who started talking might have been killed instantly

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Homology vs. Analogy• Homology: similarity by common

descent

• Analogy: similarity via independent evolutionary pathways

• When a monkey is doing X, which bears some rudimentary aspect of language, it’s difficult to know X is homology or analogy to infer about the evolutionary history

• With this in mind, we turn to a few cases that have surfaced in language and evolution in recent years that compare the cognitive abilities of humans and other species

homology

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Speech Perception

• Categorical perception: bah~pah

• once held to be uniquely human and uniquely linguistic

• this has been disconfirmed: recall that chinchillas, monkeys etc. can do CP as well

• Tracking prosody to identify speech in language learning

• rodents and monkeys can do that too

• But none of these touches on the core element of language: the combinatorial infinity of phonology, morphology, and syntax

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Starling Syntax (NY

Times)

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Monkey Business

Fitch & Hauser (2004, Science): cotton-top tamarin

A={ba, di, yo, tu, la, mi, no, wu}: female voice

B={pa, li, mo, ku, ka, bi, do, gu}: male voice

matched for duration, loudness

Are monkeys good at pattern matching?

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Monkey Syntax?

Played a sequence of syllable, of the following patterns

(AB)n = AB, ABAB, ABABAB ...

no li ba pa, la pa wu mo no li

AnB

n = AB, AABB, AAABBB

yo la pa do, ba la tu li pa ka

“Training” by exposure to a pattern

“Test” by playing a sequence than violates the training pattern

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Monkey Syntax?

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Monkey Syntax?

Such experiments are often difficult to interpret:

There could be other cognitive or processing mechanisms that affect the ability to learn these patterns

But one possibility is that monkeys do not have language: they really don’t

They lack the cognitive/computational capacity to process AnBn patterns, which are the minimum requirement for the design of human language

This may be the right kind of research question to pursue

Morphology

• All languages have morphology

• We create morphological classes from data with remarkable accuracy

• In languages like Italian or Spanish, children produce correct agreement in over 98% of the contexts from the beginning of speech

• They seem to place words into their appropriate classes very accurately

• In English past tense, children over-regularize (about 10% of the time) but they do not over-irregularize (about 0.2%)

• i.e. they say “bring-bringed”, and do not say “bring-brang”

• Categories are discrete rather than based overall similarity (which would have produced think-thunk, flow-flew)

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Categorization (Medin et al. 1987)

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One dimensional sort

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Learning in a maze

• Many species learn to match the probabilities of events/rewards/etc. in the environment when they make choices

• They do not, for instance, go for the most prominent/frequent choice

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Learning both languages

• In “bilingual” environments, children acquire both options, closely matching the frequencies of their usage

• Here “bilingual” could mean two alternative choices in phonology, morphology, or syntax, like some of the sociolinguistic variation to be discussed on Wednesday

• In monolingual environments, children go through a period of time trying both the target and the non-target forms, which are given by Universal Grammar, before settling on the target

• These strongly suggest that at some level, the mechanisms of language learning are the same as those used in running the maze, and evolutionarily ancient

• These mechanisms in turn pose constraintson, or explain, the properties of human language

Conclusion

• To understand language evolution, we need to partition the properties of languages into distinct components and hope to find them in other cognitive/perceptual systems and in other species (Hauser, Chomsky & Fitch 2002)

• The irreducible components must be uniquely human and evolved recently (but don’t expect to trace them to a single gene)

• Of course, that begs the question of how the shared components evolved, which may be cognitive and leave little trace behind, and we are back to Lewontin.

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Into the wild• There are many other linguistics courses that deal

with various subfields in depth: feel free to explore them.

• The field of linguistics is becoming increasingly inter-disciplinary

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