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Stromswold, Genetics & Evolution of Language Montreal, 2010 Genetics & the Origins of Language Karin Stromswold (karin@ruccs.rutgers.edu) Psychology Dept. & Center for Cognitive Science Rutgers University - New Brunswick .

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Stromswold, Genetics & Evolution of Language

Montreal, 2010

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  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Genetics & the Origins of Language

Karin Stromswold (karin@ruccs.rutgers.edu)

Psychology Dept. & Center for Cognitive Science Rutgers University - New Brunswick

.

Portions of this work were supported by grants from NSF (BCS-9875168, BCS-0002010, BCS-0042561, BCS- 0124095, BCS-0446838), NIH (HD37818), the Charles & Johanna Busch Biomedical Research Fund and the Bamford-Lahey Children's Foundation.

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

With many thanks to …

  • Ellyn Sheffield (former postdoc, now at Towson U.)
  • Lab Manager: Diane Molnar
  • A small army of research assistants and undergraduate students
  • 1400+ parents & children who participated in the PEGI (Prenatal

Environment & Genetic Interaction) project

  • NSF (BCS-0446838; BCS-9875168, BCS-0002010, BCS-0042561, BCS-0124095)), Charles

& Johanna Busch Biomedical Research Fund, Bamford-Lahey Children's Foundation

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Stromswold, Genetics & Evolution of Language

Montreal, 2010

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  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Outline

  • How genetic findings can inform evolutionary theories
  • f language
  • Genetic factors & language
  • What we know

– [Molecular genetics - Enard - 6/24] – Family aggregation studies – Adoption studies – Twin studies

  • [What we don’t know]
  • Evolutionary implications of genetic findings
  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Genetics vs. Heritability of Language

  • Genetic of language: If innate predispositions or neural structures enable us

to use/acquire language, they must be encoded in our DNA

  • Heritability (h2) of language: estimate of the extent to which genetic factors

account for observed variance in a trait

  • Why we might fail to find evidence for significant h2’s

– Genetic factors not important for language – Environmental factors swamp genetic factors – People are linguistically identical: if there is no variation, h2 = 0, even if genetic

factors determine a trait

Chomsky (1980): Language is like number of fingers Lieberman (1984): Language is like height

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  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Variability in Language Acquisition

  • Specific Language Impairment (SLI):

– 5-10% of children have unexplained spoken language impairments

  • Variability in rate of acquisition in normal children

– Phonology (e.g., Sander, 1972, Vihman, 1990) – Vocabulary (e.g., Goldfield & Reznick, 1990, Fenson et al., 1994), – Morphology (e.g., Brown 1973, deVilliers & deVilliers, 1973), – Syntax (e.g., Stromswold 1990, 1995, Snyder & Stromswold 1997)

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Variability in Adult Language

  • SLI in adults:

– 50% of SLI children grow up to be language impaired

  • Variability in normal adults’ linguistic proficiency:

– Verbal fluency (e.g., Day, 1979) – Interpretation of compound nouns (e.g., Gleitman & Gleitman, 1970) – Sentence processing (e.g., Bever et al., 1989, King & Just, 1991; Corley & Corley,

1995)

– Grammaticality judgments (e.g., Ross, 1979; Nagatu, 1992; Cowart, 1994). – Second language acquisition (e.g., Fillmore, 1979; deKeyser, 2000, Dornjei,

2005)

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  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Genetics & the Evolution of Language

  • If language h2’s are significant, then genetic factors play some role in language

acquisition or linguistic proficiency obtained

– It does not mean that genetic factors do play a role for “normal” people – It does not mean that the genetic factors are specific to language or subcomponents of language

  • Significant language h2’s mean that genetic variance exists now
  • Genetic variance for language means something that contributes to linguistic ability

could have been selected for.

– It does not mean that it was selected for – Even if it was selected for, it does not say what was selected for

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Pathological & Normal Variance: Fingers

Length of fingers: significant h2 for pathological & normal variance Number of fingers: significant h2 for pathological variance only

Polydactyly Oligodactyly Arachnodactyly Brachydactyly Long fingers Stubby fingers

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  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Normal & Impaired Language h2’s

  • Possibility 1: SLI h2 = normal language h2
  • Possible interpretation: Same genetic factors for SLI & normal language
  • Possibility 2: SLI h2 > normal language h2
  • Possible interpretation: Genetic factors affect both SLI and normal language,

but some that only affect SLI language (“length of fingers”)

  • Possibility 3: only SLI h2 is significant
  • Possible interpretation: Genetic factors only account for SLI variance

(“number of fingers”)

  • Evolutionary implications of Possibilities 2 & 3
  • If SLI h2 ≠ normal language h2, this is consistent with unique neural

underpinnings and/or evolutionary history for language in two groups

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Selectivity of Language h2’s

Do genetic factors selectively affect some aspect(s) of language?

– Spoken vs. written language – Expressive vs. receptive language – Subcomponents of language (phonology, lexicon, morphology, syntax, discourse etc.) – Competence vs. performance: (e.g., the rat the cat chased fled)

Evolutionary implications

– If different h2’s for different aspects of language, different genetic factors may be involved (see “Specificity”)

  • This is consistent with different aspects of language having unique neural

underpinnings and/or evolutionary history

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Selection & Competence/Performance

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Specificity of “Language” h2’s

Do the same genetic factors affect linguistic & nonlinguistic abilities?

  • Genetic overlap for linguistic & nonlinguistic abilities is consistent with

them having shared neural underpinnings and/or evolutionary history

Do the same genetic factors affect different aspects of language?

  • Genetic overlap for subcomponents of language is consistent with them

having shared neural underpinnings and/or evolutionary history

Are there genetic factors that are specific to specific aspects of language?

  • Lack of genetic overlap for subcomponents of language is consistent with

them having unique neural underpinnings and/or evolutionary history

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  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010
  • FOXP2-CNTNAP2 gene (see Enard’s talk on Thursday)

– Autosomal dominant disorder with core symptom being speech dyspraxia – All and only affected KE family members have aberrant form of FOXP2 – Not a common cause of spoken language impairment: 10+ studies haven’t found it – [In Vernes et al., core endophenotype for CNTNAP2 was nonword repetition]

  • Other loci linked to spoken language impairments (13q21: 16q24; 19q13: 1p36, 2p15, 6p21, 15q21, 2p22;

1p22; 2q31; 15q13]

  • Loci are not specific

– Same loci linked to different “phenotypes” of SLI – Most loci are also linked to written language disorders – Most loci are also linked to other neuropsychological disorders (autism, Tourette’s, ADHD, schizophrenia, bipolar)

  • Are these bi-linkages merely coincidental (the loci encompass 1000s of genes)?

Or do they indicate that the same genotype may be expressed in different ways?

  • What are the evolutionary implications of these bilinkages?

[Molecular Genetics of SLI]

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

The KE Family: Clearly AD, but disorder not specific to language

  • Core deficit: Difficulty with articution of speech
  • ? Grammatical deficits
  • Low nonverbal IQ
  • Nonverbal learning disorders

KE family: AD Oral-Motor Disorder

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AS: Another Case of AD Speech Dyspraxia?

  • AS's paternal grandfather has a severe speech/language dysfluency, presumably from birth. Short sentences, frequent
  • AS’s paternal grandfather has 2 sisters with possible mild dysfluency and 1 brother with intact speech/language.
  • AS's father is an only child and has no history of speech/language or learning disorder. (very mild stutter?)
  • AS's mother has 1 brother and 1 half-brother. No history of language/speech or learning disorder on maternal side
  • AS has an older sister who has normal speech/language development, but may have a mild learning disability.
  • AS has 4 older half-siblings (same mother), all with no history of speech/language or learning disability.

Key: Circle = female, Square = male, Diamond = not known Black = impaired, White = normal, Hatched = learning disability

Stuttered as a child

From Stromswold (2009)

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Other Families with High Rates of Language Impairment

(from Stromswold, 1998, Human Biology)

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Family Aggregation Studies

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Language Disorders Do Cluster in Families

  • Meta-analyses of 18 family aggregation studies:

Adapted from Stromswold (1998), Human Biology

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Adoption Study

  • Rationale: If genes are important for a trait, adopted children’s abilities will resemble their biological

relatives’ abilities more than their adopted relatives’ abilities.

  • One large (N>300) longitudinal study comparing adopted & non-adopted children’s skills with those of

their biological and adopted parents and siblings.

– Positive biological family history was the best predictor of language disorders – 25% of children with + biological family history were impaired (9% with + adopted FH)

  • Heritable factors affect verbal abilities more than other types of abilities
  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Twin Studies of Language

  • Rationale of twin studies:

– Monozygotic (MZ) cotwins share ~ 100% environment, ~100% alleles – Dizygotic (DZ) cotwins share ~ 100% environment, ~50% alleles

⇒ Can quantify the relative importance of DNA and environment by comparing the linguistic similarity of MZ cotwins and DZ cotwins

  • Twin studies can be used to quantify the role of:

– Additive genetic factors (A) and non-additive genetic factors (D) – Shared environment (C): environment both twins experience – Nonshared environment (E): environment only one twin experiences

  • Many twin studies show that genetic factors affect language development

– Meta-analysis (see Stromswold, 2001, Language)

  • About 1/2 to 2/3 of language-impaired twins’ language
  • About 1/4 to 1/2 of typically-developing (normal) twins’ language

– Perinatal Environment & Genetic Interaction (PEGI) Study (see Stromswold 2006, Cognition)

  • Phonology: 68% genetic
  • Lexicon: 40% genetic
  • Syntax: 69% genetic
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PEGI Study

  • Participants

– N = 542 twin pairs (all analyses performed on same sex twins)

  • 208 monozygotic (MZ)
  • 170 same sex dizygotic (DZ)
  • 164 opposite sex DZ

– Age: Between 2 and 6 years old – Sex: 56% male, 44% female – Birth Weight = 2350 grams – Gestational Age at Birth (GA) = 35.3 weeks

  • Wide range of abilities assessed

– Linguistic measures:

  • Articulation, lexical access, receptive vocabulary, syntax, pragmatics

– Nonlinguistic measures:

  • Gross motor, fine motor, oral-motor, social and cognitive
  • Extensive information about perinatal environment
  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Language Impaired PEGI Twins

Concordant twins: Both twins are language impaired Discordant twins: Only one cotwin is language impaired

  • Genetic factors account for 82% of language disorders in PEGI

twins

D Z D Z M Z M Z

20 40 60 80 100

Discordant Concordant % % of

  • f twins

twins

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  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Genetics of SLI: Non-Mendelian

  • Most genetic language disorders don’t have classic Mendelian transmission.. Review of lit shows

– Not AD: At most one-third of probands has 1 affected parent: – Not AR:

  • At most one-quarter of probands have 2 affected parents:
  • At most one-third of siblings are impaired:

– Not XLR: Sex ratios generally between 2:1 to 3:1.

  • Adoption: not 100% genetic
  • Twin studies: not 100% genetic
  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Language-Impaired & Normal Twins

Articulation Articulation Vocabulary Vocabulary Syntax Syntax General 20 20 40 40 60 60 80 80 100 100 Additive Genetic Additive Genetic Dominant Genetic Dominant Genetic Shared Environment Shared Environment NonShared Environment NonShared Environment

Language Impaired

% % of

  • f Variance (SEM)

(SEM)

Articulation Articulation Vocabulary Vocabulary Syntax Syntax General 20 20 40 40 60 60 80 80 100 100 Additive Genetic Additive Genetic Dominant Genetic Dominant Genetic Shared Environment Shared Environment NonShared Environment NonShared Environment

Normal Normal

% % Variance (SEM) (SEM)

  • Genetic factors account for more of the linguistic variance in language-

impaired (LI) than normal twins

  • Dominant genetic factors only play a role for LI twins
  • For LI and normal twins, genetic factors affect vocabulary the least
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Selectivity: Linguistic Abilities (LI + Normal twins)

Heritable factors account for different amounts of variance for different aspects of language:

Vocabulary < Syntax < Articulation < General

Vocabulary Vocabulary Syntax Syntax Articulation Articulation General 20 20 40 40 60 60 80 80 100 100 Additive Genetic Additive Genetic Dominant Genetic Dominant Genetic Shared Environment Shared Environment NonShared Environment NonShared Environment

All All Twins Twins

% % Variance (SEM) (SEM)

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Selectivity: Non-Linguistic Abilities (LI + Normal twins)

Heritable factors account for different amounts of variance for different non-linguistic abilities:

Oral Motor < Fine Motor < Cognitive < Gross Motor < Social < General

Oral Motor Fine Motor Motor Cognitive Cognitive Gross Motor Social General 20 20 40 40 60 60 80 80 100 100 Additive Genetic Additive Genetic Dominant Genetic Dominant Genetic Shared Environment Shared Environment NonShared Environment NonShared Environment

All All Twins Twins

% % Variance (SEM) (SEM)

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Specificity &Bivariate Analyses

  • Bivariate analyses: Compare twin’s performance on test A with

cotwin’s performance on test B

– Bivariate heritability, hb

2: Extent to which genetic factors account for the

phenotypic correlation between test A and test B – Genetic correlation, Rg: Extent to which the same genetic factors affect A and B regardless of their contribution to the correlation between A and B

  • hb

2 can be low and Rg high:

– e.g., genetic factors play a modest role for A and B, but the same genetic factors affect both A and B

  • hb

2 can be high and Rg low:

– e.g., genetic factors play a substantial role for A & B, but different genetic factors affect A and B

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Genetic Overlap Between Linguistic & Non-Linguistic ASQ Scores

The amount of genetic overlap between linguistic and nonlinguistic ability differs for nonlinguistic skills Gross Motor < Cognitive < Social < Fine Motor

GrossMotor-Language GrossMotor-Language Cognitive-Language Social-Language Social-Language FineMotor-Language 0.0 0.0 0.2 0.2 0.4 0.4 0.6 0.6 0.8 0.8 1.0 1.0 Bivariate Heritability Bivariate Heritability Genetic Correlation Genetic Correlation

All All Twins Twins

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Genetic Overlap Between Linguistic & Non-Linguistic Therapy

The amount of genetic overlap between linguistic and nonlinguistic ability differs for nonlinguistic skills:

(Cognitive) < Psych = Gross Motor < Fine Motor = Oral Motor

Psych-SpeechLang PT-SpeechLang PT-SpeechLang OT-SpeechLang FeedTx-SpeechLang 0.0 0.0 0.2 0.2 0.4 0.4 0.6 0.6 0.8 0.8 1.0 1.0 Bivariate Heritability Bivariate Heritability Genetic Correlation Genetic Correlation

All All Twins Twins

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Genetic Overlap for Language Milestones

Little genetic overlap for babbling & other language milestones

=> different genetic factors for babbling?

Babble-Word Babble-Word Babble-Artic Babble-Sentence Word-Artic Sentence-Artic Sentence-Word 0.0 0.0 0.2 0.2 0.4 0.4 0.6 0.6 0.8 0.8 1.0 1.0

Bivariate Heritability Bivariate Heritability Genetic Correlation Genetic Correlation

All All twins

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Overlap for Subcomponents of Language

The genetic overlap between aspects of language differs: Vocabulary-Syntax = Vocabulary-Articulation < Articulation-Syntax

=> Genetic overlap is not just a reflection of expressive vs. receptive measure

Vocabulary-Articulation Vocabulary-Syntax Articulation-Syntax Articulation-Syntax 0.0 0.0 0.2 0.2 0.4 0.4 0.6 0.6 0.8 0.8 1.0 1.0 Bivariate Heritability Bivariate Heritability Genetic Correlation Genetic Correlation

All All Twins Twins

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Genetics of Language: Clues

  • Genetic Findings:

– Genetic factors play a non-negligible role in language – Genetic factors affect normal and language-impaired people’ language (greater impact on language-impaired) – Genetic factors affect all aspects of language – Some genetic factors are not specific to language – Some genetic factors are specific to language – Some genetic factors are specific to parts of language:

  • [Environmental Findings:]

– Biological environment has a large effect on language – Psychosocial environment has a relatively modest effect on spoken language

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Genetics of Language: Complexities

  • Genotype-phenotype mapping: pleiotropy & phenocopy
  • Developmental problem: phenotypes change
  • Interactions

– Gene-gene interactions – Environment-environment interactions: – Gene-environmental interactions

  • Causality: direct vs. indirect genetic effects
  • Specificity
  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Complexities: Genotype-Phenotype Mapping

  • Pleiotropy: One genotype: many phenotypes.

Genetic oral motor dyspraxia

– Feeding problem – Mutism: unwilling or unable to speak in any situation (mutism) – Selective mutism: unable/unwilling to speak in selective situations – Speech dyspraxia – Dysfluency – Omission of phonologically unstressed elements (i.e., grammatical morphemes) – Incomplete penetrance: have the genotype but are clinically normal

  • Phenocopy: One phenotype: many genotypes.

“Grammatical SLI”

– Genetic disorder that selectively impairs syntax – Genetic speech dyspraxia – Genetic disorder that impacts auditory processing (e.g., auditory STM, auditory sequencing, , rapid auditory processing) – Genetic disorder affecting multiple aspects of language but not nonverbal cognition – Genetic disorder affecting multiple areas of development, but it is most apparent with morphosyntax (it’s a developmental “stress test”)

  • Advantage of studying genetics of abnormally good linguistic ability
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Still More Complexities …. Causality & Specificity

  • Causality problem: direct vs. indirect genetic effects

– Direct: Child has the language disorder “gene(s)” – Indirect: Parent with the language disorder gene(s) provides suboptimal linguistic input (DLEH)

  • Specificity problem

– FOXP2/CNTNAP2: NWR endophenotype; autism – What about KE family & “generic” SLI children’s non-linguistic problem – Familial Dysautonomia (IKBKAP gene at 9q31).

  • Profound oral motor dyspraxia resulting in very poor speech
  • Normal IQs, normal psychologically, normal nonverbal learning
  • But they also have ANS problems (BP, HR, temperature) & motoric delays
  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Impaired & Normal Language & Evolution

1. Genetic factors play a substantial role for LI language than “normal” language

⇒ Some language-related ability may have been selected for

2. Genetic factors play a greater role for LI language than “normal” language

⇒ Different genes? ⇒ Different evolutionary history?

Less likely to reproduce? Stoppage? Fewer children? Later children?

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Genetic Selectivity and Evolution

  • 3. Genetic factors affect all aspects of language, but articulation

& syntax are affected more than vocabulary

⇒ Greater selective pressure for articulation & syntax?

  • 4. Genetic factors also play a substantial role for all nonlinguistic

abilities (with the possible exception of oral motor in normal twins).

⇒ Language h2’s are greater for LI twins because their language impairment is partly due to non-specific genetic factors?

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Genetics Specificity and Evolution

5. Genetic overlap for linguistic & non-linguistic skills

⇒ Language and Fine Motor: Shared evolutionary history? ⇒ Language and Oral Motor: Shared evolutionary history? ⇒ Language and Social Skills: Shared evolutionary history?

6. Genetic overlap is greatest for syntax and articulation

⇒ Shared evolutionary history due to their hierarchical structure?

7. Small amount of syntax-specific genes (FLN?)

⇒ Recursion? Push-down stack (working memory)? Grammatical categories?

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Phonology & Syntax are Hierarchical

  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Syntax

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Hauser, Chomsky, & Fitch (2002)

Features of human language belong to 2 categories

  • 1. Faculty of Language Broad (FLB): shared with other species
  • 2. Faculty of Language Narrow (FLN): unique to human language (recursion)
  • K. Stromswold, Summer Institute in Cognitive Science, Montreal 2010

Theories of Language Evolution

  • If not serendipity, what is the process by which the genetic factors that subserve

language came into existence? Natural selection vs. exaptation

  • Were any of the genetic factors specifically linguistic or did they all piggy-back
  • n other abilities (e.g., communication, oral motor, fine motor (object

manipulation), cognition, mental representation?

  • If some were specifically linguistic, what were their functions?

Hitch-hikingNatural Selection Precursor Language A B a1 a2 b1 b2

From Stromswold, 2010

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Thank you …

ACQUIRING WH-QUESTIONS GENE PARSING PASSIVES GENE RECURSION GENE EXCEEDING TIME LIMITS GENE