We cannot go back in time and ask people to fill out questionnaires or participate in experiments. However, we can study what their minds produced: books, paintings, sculptures, music, and so on. These cultural artefacts are the remnants of people’s past psychologies and can function as cognitive fossils of past mental states, emotions, and preferences.
In a series of projects, I have tried to quantify the evolution of several psychological traits or preferences: love, trust, parental investment, self-control. Sometimes, quantification is difficult. In theses cases. I have turned to more qualitative methods, through systematic surveys of existing comparisons between periods and countries in the academic literature. These surveys lead to a project I call the Ancient World Values Survey.

Representative papers
Baumard, N., Huillery, E., Hyafil, A. and Safra, L. (2022) The cultural evolution of love in history, Nature Human Behavior (Supplementary material, supplementary review, data and code here, as well as the Ancient World Values Survey)
Safra, L., Chevallier, C., Grèzes, J., Baumard, N. (2020) Tracking the rise of trust in history using machine learning and paintings, Nature Communication
Martin, M. & Baumard, N. (2020) The rise of prosociality in fiction preceded democratic revolutions in Early Modern Europe, PNAS
Papers
Hyafil, A. & Baumard, N. (2022) Evoked and Transmitted Culture models: Using bayesian methods to infer the evolution of cultural traits in history, Plos One
Martins, M. D. J. D., & Baumard, N., (2022) How to develop reliable instruments to measure the cultural evolution of preferences and feelings in history?, Frontiers in Psychology
Baumard, N., Huillery, E. and Zabrocki, L. (in review) The Economic Origins of Ascetic Values : Evidence from Medieval Europe
Baumard, N. (2021) From Chariclea and Theagen to Cui Yingying and Zhang Sheng: How romantic fictions inform us about the cultural evolution of pair-bonding in Eurasia. Working paper
Martin, M. & Baumard, N. (sublmitted) Loving, Fast and Slow: A Quantitative History of Tenderness and Passion
Baumard, N. (2019) Psychological Origins of the Industrial Revolution, Behavioral and Brain Sciences, Target article, Commentaries and Response, 1-63.
Boyer, P. & Baumard, N., (2017) Cognitive attractors in the evolution and diffusion of religious representations in Luther Martin and Don Wiebe (Eds.) Religion Explained: The Cognitive Science of Religion Twenty-Five Years On
Boyer, P. & Baumard, N., (2017) The diversity of religious systems: An evolutionary and cognitive framework, in Liddle and Shackelford (Eds.), The Oxford Handbook of Evolutionary Perspectives on Religion
Baumard, N., Hyafil, A. & Boyer, p. (2015) What Changed During the Axial Age: Cognitive Styles or Reward Systems?, Communicative and Integrative Biology. 8(5).
Baumard, N., Hyafil, A. Morris, I., and Boyer, P., (2015) Increased affluence explains the emergence of ascetic wisdoms and moralizing religions. Current Biology, 25(1), 10-15. (See press coverage in Science)