Thomas Haarklau Kleppestø

About

Research interests

My research interests span a wide array of topics in psychological science, yet they are interconnected by an interest in the origin, evolution, and consequences of individual differences in psychological traits.

Sadness

I am currently investigating the emotion sadness: its affective and cognitive characteristics, its evolutionary purpose—if any—and the mechanisms that can transform sadness into clinical depression.

Political psychology

In the domain of political psychology my work is focused on investigating whether humans posess inherent political and moral inclinations and the causes of variation in authoritarian traits and political attitudes. I am also currently working on researcing the psychological underpinnings of why humans engage in intergroup warfare.

Mating psychology

Another key research interest is the psychology of human mating. For example, I examine the attractiveness of psychological traits and the dynamics of assortative mating.

Collaboration

I encourage researchers and students that share an interest in these topics to get in touch if you want to collaborate.

Core interests summarized:

· Personality: Investigating the structure of non-cognitive traits, their origins, and real-life impact.

· Behavior Genetics: Investigating the genetic and non-genetic influences on trait-variation.

· Evolutionary psychology. What is the set of all human psychological adaptations and how do they work?

· Political psychology: The nature of political and moral traits, and the psychological underpinnings of political attitudes and behaviors, including war.

· Intelligence: How does human intelligence work, how did it evolve, and what generates individual differences in it?

· Evolutionary psychopathology: Examining why mental disorders exist. How can psychological adaptations make some humans vulnerable to mental disorders?

· Mating psychology: Examining the psychological mechanisms underlying mate selection and romantic relationships from an evolutionary perspective.

· Psychometrics and Quantitative Methodology: Developing and refining methods for measuring psychological phenomena, in order to improve accuracy, reliability, and validity in psychological measurement and assessment.

· Epistemology: I am interested in the philosophy of how knowledge grows. In my view, this is best explained by «evolutionary epistemology» and is severely underutilized in psychological science.

Research

Publications

2025

Kennair, Leif Edward Ottesen; Kleppestø, Thomas Haarklau. (2025) Det biologiske grunnlaget for personlighet.
Academic chapter/article/Conference paper
Eftedal, Nikolai Haahjem; Eilertsen, Espen Moen; Sunde, Hans Fredrik; Kleppestø, Thomas Haarklau; Ystrøm, Eivind; Czajkowski, Nikolai Olavi. (2025) Beyond additive genetic effects: Explaining family resemblance in school performance across millions of pairs of Norwegian relatives. Proceedings of the National Academy of Sciences of the United States of America (PNAS)
Academic article
Nordmo, Magnus; Sunde, Hans Fredrik; Kleppestø, Thomas Haarklau; Nordmo, Morten; Caspi, Avshalom; Moffitt, Terrie. (2025) Cognitive Abilities and Educational Attainment as Antecedents of Mental Disorders: A Total Population Study of Males. Psychological Science
Academic article
Sunde, Hans Fredrik; Eilertsen, Espen Moen; Kinge, Jonas Minet; Kleppestø, Thomas Haarklau; Nordmo, Magnus; Caspi, Avshalom. (2025) Parental income and psychiatric disorders from age 10 to 40: a genetically informative population study. Journal of Child Psychology and Psychiatry
Academic article

2024

Nordmo, Magnus; Kleppestø, Thomas Haarklau; Reme, Bjørn-Atle; Sunde, Hans Fredrik; Soest, Tilmann von; Torvik, Fartein Ask. (2024) The diminishing association between adolescent mental disorders and educational performance from 2006–2019. JCPP Advances
Academic article
Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Sheehy-Skeffington, Jennifer; Vassend, Olav; Røysamb, Espen; Eftedal, Nikolai Haahjem. (2024) The genetic underpinnings of right-wing authoritarianism and social dominance orientation explain political attitudes beyond Big Five personality. Journal of Personality
Academic article
Nordmo, Magnus; Sunde, Hans Fredrik; Kleppestø, Thomas Haarklau; Nordmo, Morten; Caspi, Avshalom; Moffitt, Terrie E.. (2024) Cognitive Abilities and Educational Attainment as Antecedents of Mental Disorders: A Total Population Study of Males. PsyArXiv
Academic article
Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Vassend, Olav Mandt; Røysamb, Espen; Eftedal, Nikolai Haahjem; Sheehy-Skeffington, Jennifer. (2024) Attachment and Political Personality are Heritable and Distinct Systems, and Both Share Genetics with Interpersonal Trust and Altruism. Behavior Genetics
Academic article
Sunde, Hans Fredrik; Eftedal, Nikolai Haahjem; Cheesman, Rosa; Corfield, Elizabeth C.; Kleppestø, Thomas H.; Seierstad, Anne Caroline. (2024) Genetic similarity between relatives provides evidence on the presence and history of assortative mating. Nature Communications
Academic article

2023

Nordmo, Magnus; Kleppestø, Thomas Haarklau; Sunde, Hans Fredrik; Flatø, Martin; Demange, Perline; Torvik, Fartein Ask. (2023) Author Correction: The association between parental internalizing disorders and child school performance (npj Science of Learning, (2023), 8, 1, (34), 10.1038/s41539-023-00182-x). npj Science of learning
Errata
Nordmo, Magnus; Kleppestø, Thomas Haarklau; Sunde, Hans Fredrik; Flatø, Martin; Demange, Perline; Torvik, Fartein Ask. (2023) The association between parental internalizing disorders and child school performance. npj Science of learning
Academic article
Kleppestø, Thomas Haarklau; Eilertsen, Espen Moen; Bergen, Elsje van; Sunde, Hans Fredrik; Zietsch, Brendan; Nordmo, Magnus. (2023) Intergenerational transmission of ADHD behaviors: Genetic and environmental pathways. Psychological Medicine
Academic article

2022

Sunde, Hans Fredrik; Kleppestø, Thomas Haarklau; Gustavson, Kristin; Nordmo, Magnus; Reme, Bjørn-Atle; Torvik, Fartein Ask. (2022) The ADHD deficit in school performance across sex and parental education: A prospective sibling‐comparison register study of 344,152 Norwegian adolescents. JCPP Advances
Academic article
Eftedal, Nikolai Haahjem; Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Sheehy-Skeffington, Jennifer; Røysamb, Espen; Vassend, Olav Mandt. (2022) Justice sensitivity is undergirded by separate heritable motivations to be morally principled and opportunistic. Scientific Reports
Academic article

2021

Kleppestø, Thomas Haarklau; Eilertsen, Espen Moen; Bergen, Elsje van; Zeitsch, Brendan; Sunde, Hans Fredrik; Nordmo, Magnus. (2021) Intergenerational Transmission of ADHD: More Evidence for Heritability than Fast Life History. Behavior Genetics
Abstract

2019

Kleppestø, Thomas Haarklau; Eftedal, Nikolai Haahjem; Thomsen, Lotte. (2019) Social Dominance Orientation(SDO).
Academic chapter/article/Conference paper
Kleppestø, Thomas Haarklau. (2019) Intelligence.
Academic chapter/article/Conference paper
Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Vassend, Olav; Røysamb, Espen; Eftedal, Nikolai Haahjem; Sheehy-Skeffington, Jennifer. (2019) Correlations between social dominance orientation and political attitudes reflect common genetic underpinnings. Proceedings of the National Academy of Sciences of the United States of America (PNAS)
Academic article
Ulset, Vidar; Czajkowski, Nikolai Olavi; Kraft, Brage; Kraft, Pål; Wikenius, Ellen; Kleppestø, Thomas Haarklau. (2019) Are unpopular children more likely to get sick? Longitudinal links between popularity and infectious diseases in early childhood. PLOS ONE
Academic article

2017

Kennair, Leif Edward Ottesen; Kleppestø, Thomas Haarklau. (2017) Social Anxiety.
Academic chapter/article/Conference paper
Kennair, Leif Edward Ottesen; Kleppestø, Thomas Haarklau; Jørgensen, Bjørn Emil Gloppen; Larsen, Simen Mjøen. (2017) Evolutionary Clinical Psychology.
Academic chapter/article/Conference paper
Kennair, Leif Edward Ottesen; Kleppestø, Thomas Haarklau; Larsen, Simen Mjøen; Jørgensen, Bjørn Emil Gloppen. (2017) Depression: Is Rumination Really Adaptive?.
Academic chapter/article/Conference paper
Kleppestø, Thomas Haarklau; Kennair, Leif Edward Ottesen; Jørgensen, Bjørn Emil Gloppen; Borgan, Kristina; Larsen, Simen Mjøen. (2017) Depression.
Academic chapter/article/Conference paper

2016

Larsen, Simen Mjøen; Kleppestø, Thomas Haarklau; Buss, David M.; Kennair, Leif Edward Ottesen. (2016) Repetitive thinking in a normal population: reponse to negative events. HBES - Human Behavior and evolution society - 28th Annual Meeting - Conference programme and Book of Abstracts
Abstract
Kennair, Leif Edward Ottesen; Kleppestø, Thomas Haarklau. (2016) Hva er psykopatologi?.
Academic chapter/article/Conference paper

Journal publications

Eftedal, Nikolai Haahjem; Eilertsen, Espen Moen; Sunde, Hans Fredrik; Kleppestø, Thomas Haarklau; Ystrøm, Eivind; Czajkowski, Nikolai Olavi. (2025) Beyond additive genetic effects: Explaining family resemblance in school performance across millions of pairs of Norwegian relatives. Proceedings of the National Academy of Sciences of the United States of America (PNAS)
Academic article
Nordmo, Magnus; Sunde, Hans Fredrik; Kleppestø, Thomas Haarklau; Nordmo, Morten; Caspi, Avshalom; Moffitt, Terrie. (2025) Cognitive Abilities and Educational Attainment as Antecedents of Mental Disorders: A Total Population Study of Males. Psychological Science
Academic article
Sunde, Hans Fredrik; Eilertsen, Espen Moen; Kinge, Jonas Minet; Kleppestø, Thomas Haarklau; Nordmo, Magnus; Caspi, Avshalom. (2025) Parental income and psychiatric disorders from age 10 to 40: a genetically informative population study. Journal of Child Psychology and Psychiatry
Academic article
Nordmo, Magnus; Kleppestø, Thomas Haarklau; Reme, Bjørn-Atle; Sunde, Hans Fredrik; Soest, Tilmann von; Torvik, Fartein Ask. (2024) The diminishing association between adolescent mental disorders and educational performance from 2006–2019. JCPP Advances
Academic article
Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Sheehy-Skeffington, Jennifer; Vassend, Olav; Røysamb, Espen; Eftedal, Nikolai Haahjem. (2024) The genetic underpinnings of right-wing authoritarianism and social dominance orientation explain political attitudes beyond Big Five personality. Journal of Personality
Academic article
Nordmo, Magnus; Sunde, Hans Fredrik; Kleppestø, Thomas Haarklau; Nordmo, Morten; Caspi, Avshalom; Moffitt, Terrie E.. (2024) Cognitive Abilities and Educational Attainment as Antecedents of Mental Disorders: A Total Population Study of Males. PsyArXiv
Academic article
Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Vassend, Olav Mandt; Røysamb, Espen; Eftedal, Nikolai Haahjem; Sheehy-Skeffington, Jennifer. (2024) Attachment and Political Personality are Heritable and Distinct Systems, and Both Share Genetics with Interpersonal Trust and Altruism. Behavior Genetics
Academic article
Sunde, Hans Fredrik; Eftedal, Nikolai Haahjem; Cheesman, Rosa; Corfield, Elizabeth C.; Kleppestø, Thomas H.; Seierstad, Anne Caroline. (2024) Genetic similarity between relatives provides evidence on the presence and history of assortative mating. Nature Communications
Academic article
Nordmo, Magnus; Kleppestø, Thomas Haarklau; Sunde, Hans Fredrik; Flatø, Martin; Demange, Perline; Torvik, Fartein Ask. (2023) Author Correction: The association between parental internalizing disorders and child school performance (npj Science of Learning, (2023), 8, 1, (34), 10.1038/s41539-023-00182-x). npj Science of learning
Errata
Nordmo, Magnus; Kleppestø, Thomas Haarklau; Sunde, Hans Fredrik; Flatø, Martin; Demange, Perline; Torvik, Fartein Ask. (2023) The association between parental internalizing disorders and child school performance. npj Science of learning
Academic article
Kleppestø, Thomas Haarklau; Eilertsen, Espen Moen; Bergen, Elsje van; Sunde, Hans Fredrik; Zietsch, Brendan; Nordmo, Magnus. (2023) Intergenerational transmission of ADHD behaviors: Genetic and environmental pathways. Psychological Medicine
Academic article
Sunde, Hans Fredrik; Kleppestø, Thomas Haarklau; Gustavson, Kristin; Nordmo, Magnus; Reme, Bjørn-Atle; Torvik, Fartein Ask. (2022) The ADHD deficit in school performance across sex and parental education: A prospective sibling‐comparison register study of 344,152 Norwegian adolescents. JCPP Advances
Academic article
Eftedal, Nikolai Haahjem; Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Sheehy-Skeffington, Jennifer; Røysamb, Espen; Vassend, Olav Mandt. (2022) Justice sensitivity is undergirded by separate heritable motivations to be morally principled and opportunistic. Scientific Reports
Academic article
Kleppestø, Thomas Haarklau; Eilertsen, Espen Moen; Bergen, Elsje van; Zeitsch, Brendan; Sunde, Hans Fredrik; Nordmo, Magnus. (2021) Intergenerational Transmission of ADHD: More Evidence for Heritability than Fast Life History. Behavior Genetics
Abstract
Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Vassend, Olav; Røysamb, Espen; Eftedal, Nikolai Haahjem; Sheehy-Skeffington, Jennifer. (2019) Correlations between social dominance orientation and political attitudes reflect common genetic underpinnings. Proceedings of the National Academy of Sciences of the United States of America (PNAS)
Academic article
Ulset, Vidar; Czajkowski, Nikolai Olavi; Kraft, Brage; Kraft, Pål; Wikenius, Ellen; Kleppestø, Thomas Haarklau. (2019) Are unpopular children more likely to get sick? Longitudinal links between popularity and infectious diseases in early childhood. PLOS ONE
Academic article
Larsen, Simen Mjøen; Kleppestø, Thomas Haarklau; Buss, David M.; Kennair, Leif Edward Ottesen. (2016) Repetitive thinking in a normal population: reponse to negative events. HBES - Human Behavior and evolution society - 28th Annual Meeting - Conference programme and Book of Abstracts
Abstract

Part of book/report

Kennair, Leif Edward Ottesen; Kleppestø, Thomas Haarklau. (2025) Det biologiske grunnlaget for personlighet.
Academic chapter/article/Conference paper
Kleppestø, Thomas Haarklau; Eftedal, Nikolai Haahjem; Thomsen, Lotte. (2019) Social Dominance Orientation(SDO).
Academic chapter/article/Conference paper
Kleppestø, Thomas Haarklau. (2019) Intelligence.
Academic chapter/article/Conference paper
Kennair, Leif Edward Ottesen; Kleppestø, Thomas Haarklau. (2017) Social Anxiety.
Academic chapter/article/Conference paper
Kennair, Leif Edward Ottesen; Kleppestø, Thomas Haarklau; Jørgensen, Bjørn Emil Gloppen; Larsen, Simen Mjøen. (2017) Evolutionary Clinical Psychology.
Academic chapter/article/Conference paper
Kennair, Leif Edward Ottesen; Kleppestø, Thomas Haarklau; Larsen, Simen Mjøen; Jørgensen, Bjørn Emil Gloppen. (2017) Depression: Is Rumination Really Adaptive?.
Academic chapter/article/Conference paper
Kleppestø, Thomas Haarklau; Kennair, Leif Edward Ottesen; Jørgensen, Bjørn Emil Gloppen; Borgan, Kristina; Larsen, Simen Mjøen. (2017) Depression.
Academic chapter/article/Conference paper
Kennair, Leif Edward Ottesen; Kleppestø, Thomas Haarklau. (2016) Hva er psykopatologi?.
Academic chapter/article/Conference paper

Teaching

Courses

Outreach