Willoughby, Emily2021-04-122021-04-122020-12https://hdl.handle.net/11299/219333University of Minnesota Ph.D. dissertation. 2020. Major: Psychology. Advisors: James Lee, Matt McGue. 1 computer file (PDF); 206 pages.The work included in this dissertation represents empirical inquiries into three areas of cause and consequence for individual differences in human intelligence: How molecular genetic data can be used to draw inference about environmental mechanisms, how intelligence relates to information processing in the brain, and whether intelligence is meaningfully malleable by parental influence into adulthood. Study 1 uses polygenic scores derived from a large GWAS of educational attainment to demonstrate “genetic nurture”, through which the unique genetics of parents can give rise to passive gene-environment correlation that affects their offspring’s years of education. Study 2 explores the observation that faster reaction time (RT) on elementary cognitive tasks (ECTs) is associated with higher g. By partitioning stimuli into perceptual and decisional stages of information flow, we show through both additive-factors logic and diffusion modeling that g is expressed uniquely in the decisional, but not perceptual, stage of processing. Finally, Study 3 examines the sources of variance in IQ in a fully adult sample of adoptive and biological families to provide new evidence about the extent of IQ’s malleability. We find that the environment fostered by the parents explains less than 3% of the variance in their offspring’s IQ scores in adulthood. In sum, the converging operations afforded by twin and adoption studies, GWAS, and ECTs can address crucial questions of causal inference in human intelligence.enBehavior geneticsIndividual differencesIntelligenceThesis or Dissertation