Keynote Speakers for ICSD 2026

hisashi ohtsuki

SOKENDAI (The Graduate University for Advanced Studies)

Mathematical Biology, Evolutionary Game Theory, Social Evolution, Indirect Reciprocity

Biography

Hisashi Ohtsuki is a theoretical evolutionary biologist and currently an Associate Professor at SOKENDAI (the Graduate University for Advanced Studies) in Hayama, Japan. He received his PhD degree in biology from Kyushu University in 2006. He was a postdoctoral fellow at the Program for Evolutionary Dynamics, Harvard University, and a PRESTO researcher at the Japan Science and Technology Agency. One of his main interests is in social evolution theory. Using evolutionary game theoretic models, he studies evolutionary mechanisms of how cooperation is established and stably maintained in a population. He is a winner of the JSMB Early Career Award, the Young Scientist's Award by MEXT, and the JSPS Prize.

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Selected Publications

Fujimoto, Y. & Ohtsuki, H. (2023). Evolutionary stability of cooperation in indirect reciprocity under noisy and private assessment. Proceedings of the National Academy of Sciences of the United States of America, 120(20), e2300544120, https://doi.org/10.1073/pnas.2300544120
Kristensen, N.P., Ohtsuki, H. & Chisholm, R.A. (2022). Ancestral social environments plus nonlinear benefits can explain cooperation in human societies. Scientific Reports, 12, 20252, https://doi.org/10.1038/s41598-022-24590-y
Ohtsuki, H. (2018). Evolutionary dynamics of coordinated cooperation. Frontiers in Ecology and Evolution, 6, 62, https://doi.org/10.1038/s41598-022-24590-y
Reeves, T., Ohtsuki, H. & Fukui, S. (2017). Asymmetric public goods game cooperation through pest control. Journal of Theoretical Biology, 435, 238-247, https://doi.org/10.3389/fevo.2018.00062
Tanaka, H., Ohtsuki, H. & Ohtsubo, Y. (2016). The price of being seen to be just: an intention signalling strategy for indirect reciprocity. Proceedings of the Royal Society B, 283(1835), 20160694, https://doi.org/10.1016/j.jtbi.2017.09.006

Kazutoshi Sasahara

Institute of Science Tokyo

Computational Social Science, Fake News, Deepfake, Social AI

Biography

Kazutoshi Sasahara received his Ph.D. from Graduate School of Arts and Sciences, The University of Tokyo in 2005. He held positions as Assistant Professor and Lecturer at Graduate School of Informatics, Nagoya University, and Associate Professor and Professor at School of Environment and Society, Tokyo Institute of Technology. He is currently a Professor at School of Environment and Society, Institute of Science Tokyo. He was a Visiting Researcher at UCLA in 2009 and at Indiana University in 2016. He also served as a JST PRESTO Researcher from 2016 to 2020. His expertise is in computational social science, with a focus on the science of fake news. He received the Excellence Award in the Social Sciences Category of the DOCOMO Mobile Science Award in 2024.

Webpage

Selected Publications

Xu, W., Sasahara, K., Chu, J., Wang, B., Fan, W., & Hu, Z. (2025). Social media warfare: Investigating human-bot engagement in English, Japanese, and German during the Russo–Ukrainian war on Twitter and Reddit. EPJ Data Science, 14(10). https://doi.org/10.1140/epjds/s13688-025-00528-y
Miyazaki, K., Uchiba, T., Tanaka, K., An, J., Kwak, H., & Sasahara, K. (2023). “This is Fake News”: Characterizing the spontaneous debunking from Twitter users to COVID-19 false information. Proceedings of the International AAAI Conference on Web and Social Media, 17(1), 650–661. https://doi.org/10.1609/icwsm.v17i1.22176
Ghasiya, P., Ahnert, G., & Sasahara, K. (2023). Identifying themes of right-wing extremism in Hindutva discourse on Twitter. Social Media + Society, 9(3), 2023D. https://doi.org/10.1177/20563051231199457
Gamage, D., Ghasiya, P., Bonagiri, V. K., Whiting, M. E., & Sasahara, K. (2022). Are deepfakes concerning? Analyzing conversations of deepfakes on Reddit and exploring societal implications. Proceedings of the 2022 CHI Conference on Human Factors in Computing Systems (CHI ’22), 103, 1-19. https://doi.org/10.1145/3491102.3517446
Xu, W., & Sasahara, K. (2022). Characterizing the roles of bots on Twitter during the COVID-19 infodemic. Journal of Computational Social Science, 5, 591–609. https://doi.org/10.1007/s42001-021-00139-3
Sasahara, K., Chen, W., Peng, H., Ciampaglia, G. L., Flammini, A., & Menczer, F. (2021). Social influence and unfollowing accelerate the emergence of echo chambers. Journal of Computational Social Science, 4(1), 381–402. https://doi.org/10.1007/s42001-020-00084-7

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