Intelligence: The Dynamics of Intelligence Part six Does intelligence remain stable over a lifetime or does it change? Are individuals on opposite ends of the spectrum really that different?

Intelligence: The Dynamics By age 4, children’s performance on intelligence tests begins to predict their adolescent & adult scores High scoring adolescents tend to have been early readers Intelligence scores become stable after about 7 years of age In numerous studies, consistency of intelligence scores has been determined to increase with age

Intelligence: The Extremes of Intelligence Part seven

Intelligence: The Extremes (Low) Intellectual Disability/Developmentally Delayed (Mental Retardation) A condition characterized by limited mental capacity Indicated by a low test score (<70) and difficulty adapting to the normal demands of independent living; before the age of 18 1-3% of the population An estimated 6.2 to 7.5 million Americans Male to female ratio?

Intelligence: The Extremes (Low) The three most common biological causes… Down Syndrome A condition of intellectual disability & associated physical disorders 47 chromosomes, as opposed to 46 (an extra 21st) Fetal Alcohol Syndrome Fragile X Syndrome A condition in which a male has a defect in a gene on the X chromosome of the twenty- third pair Leads to a deficiency in a protein needed for brain development

Intelligence: The Extremes (Low) Other Causes? Environmental Factors Lead poisoning Prenatal exposure to mercury Poor nutrition Lack of mental stimulation Familial Intellectual Disabilities A developmental delay related to living in poverty; generally produces relatively intellectual disability.

Intelligence: The Extremes (High) Definitions of giftedness (>130) vary considerably 2% of the population is >130 (gifted) ½% of the population >140-145 (genius) Misconceptions about the high extreme “Early ripe, early rot…” Socially awkward, physically weak, more likely to suffer from mental illness, etc. The “mad scientists” or “evil geniuses”

Intelligence: The Extremes (High) Lewis Terman (1921) Terman’s “Termites” Longitudinal Study of 1,528 children IQs ranging from 130 – 200 Findings Gifted individuals tend to be above average in… Physical health Emotional adjustment Mental health Social maturity

Intelligence: Heredity & Environment Part eight

Intelligence: Heredity & Environment Early pioneers of intelligence… Maintained the nature view of intelligence Today’s nature theorists… Assert that a child’s intelligence CANNOT be changed; genetic destiny Many argue that this downplays the value of special education programs for underprivileged groups

Intelligence: Heredity & Environment Today’s nurture theorists… Assert that traits with a strong genetic component are not necessarily unchangeable Argue that even MORE funds be allocated for remedial programs, especially in lower- income areas

Evidence for Hereditary Influence

Intelligence: Heredity & Environment Family Studies Can determine only whether genetic influence on a trait is plausible Twin Studies The average correlation for identical twins is +0.86 The average correlation for fraternal twins is +0.60 Adoption Studies Studies indicate that there is more than chance similarity between adopted children and their biological parents

Intelligence: Heredity & Environment Heritability Ratio An estimate of the proportion of trait variability in a population that is determined by variations in genetic inheritance Can be estimated for any trait 90% for height 85% for weight Intelligence?

Intelligence: Heredity & Environment Heritability estimates for intelligence vary considerably High Estimate: 80% 20% of the variation in intelligence is attributable to environmental factors Low Estimate: 40% 60% of the variation in intelligence is attributable to environmental factors

Intelligence: Heredity & Environment Limitations of heritability estimates Heritability is a group statistic; CANNOT be meaningfully applied to individuals A trait’s heritability may vary from one group to another “There really is no single fixed value that represents any true, constant value for the heritability of IQ or anything else…”

Evidence for Environmental Influence

Intelligence: Heredity & Environment Twin Studies The average correlation for identical twins raised together is +0.86 The average correlation for identical twins raised apart is +0.72 Adoption Studies There is some resemblance between adoptive parents and their children Siblings reared together are more similar in IQ than siblings reared apart (0.48, as opposed to 0.23)

Intelligence: Heredity & Environment Sandra Scarr (1991) Reaction-Range Model Heredity sets certain limits on intelligence and environmental factors determine where individuals fall within these limits Genetic makeup places an upper limit on a person’s IQ Cannot be exceeded; even when environment is ideal Genetic makeup places a lower limit on a person’s IQ except in extreme cases