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Language genes and evolution

Linguistics lecture #10

November 28, 2006

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Overview

• 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

geneprotein

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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 aretwo ______

Wug … wugness,isn’t it?

Oh, dear.

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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.

People differ in their innate language abilities.

These differences affect people’s reproductive success (so also that of the “language genes”).

FOXP2, etc…?

Seems to be true too….

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 comparisonsFossilsAncient evidence of complex cultureComputer 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…?