Dissertation
What makes us human: genomic insights into cognition, language, migration, and mental health
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2025
DOI: 10.25820/etd.008218
Abstract
This thesis investigates how ancient genetic changes shaped the traits that define our species and continue to influence how we think and act. Through four studies integrating evolutionary genomics, behavioral genetics, and psychiatric research across nearly 500,000 participants, this work demonstrates that human distinctiveness arose primarily through regulatory rewiring rather than novel proteins, with subtle changes in gene expression timing and location during brain development. These changes created the foundations for language, exploration, and self-reflection. Chapter 2 reveals that Human Ancestor Quickly Evolved Regions (HAQERs), comprising less than 0.1% of the genome, have a disproportionate effect on individual differences in human language abilities, show balancing selection across 20,000 years, and convergent evolution across vocal learning mammals. Chapter 3 establishes that migration propensity is moderately heritable (SNP h2 ∼5%), with migration-associated variants enriched around genes highly expressed in cortical excitatory neurons, and migration polygenic scores predict both ancient population movements across 10,000 years and modern regional economic growth, revealing how cognitive and motivational systems underpin human adaptability. Chapter 4 uncovers a paradox where exceptional cognitive ability is associated with a ∼6-fold higher risk for suicidal thoughts in children with autism, with polygenic scores for cognition predicting suicidal thoughts in neurodiverse populations. Chapter 5 introduces Lingo, an online phenotyping platform achieving up to 10-fold greater statistical power for genetic associations than traditional measures, enabling population-scale studies while revealing distinct genetic architectures across language components. Collectively, this work reveals that the genetic changes underlying human evolution are not relics of the past but actively contribute to present-day diversity, shaping individual differences in cognition, behavior, and mental health.
Details
- Title: Subtitle
- What makes us human: genomic insights into cognition, language, migration, and mental health
- Creators
- Lucas Casten
- Contributors
- Jacob Michaelson (Advisor)Bob McMurray (Committee Member)Hanna Stevens (Committee Member)Michael Schnieders (Committee Member)Bin He (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Genetics
- Date degree season
- Autumn 2025
- DOI
- 10.25820/etd.008218
- Publisher
- University of Iowa
- Number of pages
- xi, 223 pages
- Copyright
- Copyright 2025 Lucas Casten
- Comment
- This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: https://www.lib.uiowa.edu/sc/contact/
- Language
- English
- Date submitted
- 12/09/2025
- Description illustrations
- illustrations, graphs, tables
- Description bibliographic
- Includes bibliographical references (pages 182-223).
- Public Abstract (ETD)
- What makes us human? To try and answer that question, this thesis explores how DNA changes created our extraordinary abilities, like language, and how these same changes make each of us unique. By studying genetic data from nearly 500,000 people, we find that human traits like language didn t come from entirely new genes. Instead, human DNA changes when and where existing genes turn on in the developing brain. Remarkably, tweaks to tiny DNA regions (<0.1% of our total DNA) that evolved to control gene activity have massive effects on our ability to communicate. On average, a single change in these regions has 188 times larger effect on language skills than changes elsewhere in our DNA. Similar changes appear in other animals with complex communication skills, like bats and whales. We also discovered that our desire to explore has some genetic roots, using many of the same brain circuits for language. These genetic factors predict not just how far people move today, but also how far our ancestors migrated over the past 10,000 years and are related to many aspects of personality and health. However, the brain circuits supporting these capabilities involve trade-offs. While higher intelligence usually protects against mental health problems, children with autism and exceptional intelligence face six times higher risk of suicidal thoughts, showing that brain systems supporting complex thinking can also create emotional problems. Overall, this work reveals that the ancient DNA changes making us human also create the incredible diversity we see across people today.
- Academic Unit
- Interdisciplinary Graduate Program in Genetics
- Record Identifier
- 9985134848902771
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