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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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