Nature & Nurture Language Development
Importance of Language Development:
Early language skills are essential for:
School readiness
Academic success
Literacy skills
Earnings and mental health in adulthood
Factors Affecting Language Development:
Language abilities manifest early (first three years of life) across all cultures.
No explicit instruction is needed; it is considered an innate ability.
Key Methods to Assess Language Development:
Clinical Evaluation of Language Fundamentals (CELF): Measures both receptive and expressive language skills by comparing a child to their peers.
Evidence Supporting Nature and Nurture:
1. Twin Studies:
o Monozygotic (MZ) twins share 100% of genes, while Dizygotic (DZ) twins share 50%.
o Heritability is calculated using twin comparisons:
Heritability = 2 (rMZ – rDZ).
o Studies show language ability is influenced by both genetics and environment.
2. KE Family (Verbal Dyspraxia):
o Affected members exhibit significant speech and language impairments, due to a mutation in the FOXP2 gene.
o FOXP2 gene is essential for proper speech and language development.
3. Genetic Association Studies:
o Multiple studies (e.g., Reader et al., 2014; Landi & Perdue, 2018; Eising et al., 2022) indicate that language development is influenced by several genetic factors.
Twin Studies Key Findings:
Heritability Estimates:
Vocabulary: 26% at age 2.
Grammar: 52% in boys, 43% in girls at age 2.
By age 6, heritability increases to 44%-92%.
Limitations:
Large sample sizes are needed.
Twinning effects: Twins might show more language delays than singletons.
FOXP2 Gene and Language Evolution:
The FOXP2 gene has remained highly conserved across species, playing a critical role in speech and language functions.
Two unique amino acid substitutions in humans (compared to primates) suggest a selective advantage in human evolution.
Summary:
Both genetic and environmental factors are critical to language development.
Heritability of language skills increases with age.
Genetic factors like FOXP2 are key, but language ability results from complex gene-environment interactions.
Importance of Language Development:
Early language skills are essential for:
School readiness
Academic success
Literacy skills
Earnings and mental health in adulthood
Factors Affecting Language Development:
Language abilities manifest early (first three years of life) across all cultures.
No explicit instruction is needed; it is considered an innate ability.
Key Methods to Assess Language Development:
Clinical Evaluation of Language Fundamentals (CELF): Measures both receptive and expressive language skills by comparing a child to their peers.
Evidence Supporting Nature and Nurture:
1. Twin Studies:
o Monozygotic (MZ) twins share 100% of genes, while Dizygotic (DZ) twins share 50%.
o Heritability is calculated using twin comparisons:
Heritability = 2 (rMZ – rDZ).
o Studies show language ability is influenced by both genetics and environment.
2. KE Family (Verbal Dyspraxia):
o Affected members exhibit significant speech and language impairments, due to a mutation in the FOXP2 gene.
o FOXP2 gene is essential for proper speech and language development.
3. Genetic Association Studies:
o Multiple studies (e.g., Reader et al., 2014; Landi & Perdue, 2018; Eising et al., 2022) indicate that language development is influenced by several genetic factors.
Twin Studies Key Findings:
Heritability Estimates:
Vocabulary: 26% at age 2.
Grammar: 52% in boys, 43% in girls at age 2.
By age 6, heritability increases to 44%-92%.
Limitations:
Large sample sizes are needed.
Twinning effects: Twins might show more language delays than singletons.
FOXP2 Gene and Language Evolution:
The FOXP2 gene has remained highly conserved across species, playing a critical role in speech and language functions.
Two unique amino acid substitutions in humans (compared to primates) suggest a selective advantage in human evolution.
Summary:
Both genetic and environmental factors are critical to language development.
Heritability of language skills increases with age.
Genetic factors like FOXP2 are key, but language ability results from complex gene-environment interactions.