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Language genes and evolution
Linguistics lecture #10
November 28, 2006
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Overview
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Language and genes
Natural selection and language
Reconstructing the history of language
Language and human nature
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Language innateness:
Review of the evidence
• Universals: Every human society has
language, and they are all similar (nouns,
verbs, transformations, phonology, etc)
• Learnability: The induction and gavagai
problems imply that we need to know
something first before we can learn
• Experiments show that babies know a lot
• Brains have built-in language areas
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So is language in our genes?
• No, because nothing is “in our genes”
• A gene is just a piece of DNA that makes a
protein
gene
protein
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The discovery of genes
• Genes are the “atoms” of
heredity
• They combine in ways
that can be described
with mathematics
• So they were discovered
in the 1860s through
mathematical patterns in
heredity
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A “language gene”
• The first gene specific to language was
discovered the same way in the 1990s, by
studying a language disorder in one family
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Specific language impairment
• People with this disorder have difficulty
processing aspects of grammar, such as
grammatical word endings in English
• They say things like “The boys eat four cookie.”
This is a wug.
Here are two more of them.
These are
Oh, dear.
two ______
Wug … wugness,
isn’t it?
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Is it really specific to language?
• People with this disorder do have lower IQ
than non-impaired people
• However, there are people in this family
with equally low IQ who do not have
language problems
• So most researchers do think that the
disorder is specific to language
• Interestingly, it also affects muscle
movements of the mouth….
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Finding the gene
• Because of the regular pattern of impaired
people in this family, it must be that the
mutation of a single gene is responsible
• Comparing impaired and unimpaired
members of the family allowed this key
gene to be isolated
• Soon it was found on chromosome 7, and
was named SPCH1 (“speech 1”)
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SPCH1 = FOXP2
• More recently, SPCH1 was renamed
FOXP2, since it turned out to be similar to
another human gene already called FOXP1.
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What does FOXP2 actually do?
• Like FOXP1, FOXP2 makes a protein that
helps make other genes make other proteins
• The mouse version of FOXP2 is active
during brain development
• So human FOXP2 is just the first of a chain
of processes that ultimately, somehow,
affects the development of the brain’s
ability to process language….
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Huh? Mice have FOXP2??
• So do chimpanzees, gorillas, orangutans,
rhesus monkeys, etc, but there are differences
(… etc ...)
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How come human FOXP2 is so
similar to other animals’?
• There are two possibilities:
A. It’s just an amazing coincidence.
B. Human beings (including our genes) are
related to other living things, just as I am related
to you, and you are related to your brothers and
sisters, etc.
• Of course, scientists prefer B: evolution.
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Our friend Darwin
• Many people had argued
for evolution before
Darwin
• But Darwin was the first
person to provide a
mechanism that makes
evolution happen:
natural selection
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Natural selection
• Natural selection (and thus evolution)
occurs whenever three things are true:
Something can copy itself.
The copies are not exactly the same.
Differences in the copies affect their ability to
copy themselves again.
• Genes have all three properties, so evolution
is inevitable
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What about language?
• If human language evolved by natural
selection, those three must be true here too:
There are “language genes” that copy
themselves from parent to child. FOXP2, etc…?
People differ in their innate language abilities.
Seems to be true too….
These differences affect people’s reproductive
success (so also that of the “language genes”).
Good talkers have more kids…? Maybe so….
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Molecular evolution
• More changes in the human form of FOXP2
affect protein structure, and thus its real-life
effects, suggesting that these changes were
selected, not random
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Reconstructing history
• But what about the actual history of this
evolution?
• Scientists have used a number of methods to
try to reconstruct it
Genetic comparisons
Fossils
Ancient evidence of complex culture
Computer models
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Language fossils
• Fossilized skulls show brains getting bigger
(including language areas), and tongues
getting rounder (to move more easily)
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Ancient culture
• If culture (e.g. religion) requires language,
did the Neanderthals (尼安德塔人) who
buried their dead have language?
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Modeling language evolution
• For example, you can model the brain with
a connectionist network
• Then let it have “babies” that have slightly
different “innate” connections
• Put many such networks into a virtual
“community”
• Result: If it affects their survival, the
networks will evolve some innate language
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Chomsky vs. Darwin
• Chomsky believes language is innate, right?
• Surprisingly, he has also often argued that
language did NOT evolve by natural
selection:
“It would be a serious error to suppose that all
properties [of the brain, e.g. language] can be
‘explained’ in terms of natural selection.”
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Summary
• There are “language genes”, but their
relation with language is complex
• These genes evolved from genes in other
animals, where they had a different function
• Fossils, ancient culture, and modeling can
also help reconstruct language evolution
• What does Chomsky believe…?
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