Yoh Iwasa is a professor emeritus at Kyushu University, Japan. He received PhD from Kyoto University (Theoretical Biophysics) in 1980. After postdoctoral studies at Stanford and Cornell, he joined the faculty of Department of Biology, Kyushu University in 1985. Dr Yoh Iwasa started his carrier in the theoretical study of ecology, evolution, and animal behavior, including the evolution of mate preference, the dynamics of tropical forests, and social-ecological coupled dynamics for ecosystem management. More recently he has also been working on biological rhythm, cancer, development, and immune system, as well as cultural/social studies. He has repeatedly found that the same mathematical and computational methods are applicable to diverse branches of biology, and similar concepts are able to give insights in different subfields of life sciences. Director, Institute of Advanced Study Kyushu University (since 2010). FHM of American Academy of Arts and Sciences (since 2006).
EDUCATION
1975 B Sc Kyoto University, Japan
1980 Ph.D Kyoto University, Japan
RESEARCH INTERESTS
mathematical biology
378
Scopus Publications
45779
Scholar Citations
84
Scholar h-index
288
Scholar i10-index
Scopus Publications
Is Thymic Involution Truly a Deterioration or an Adaptation? Yoh Iwasa, Rena Hayashi, Akane Hara, Kosei Matsuo Bulletin of Mathematical Biology, 2026 In mammals, the immune system recognizes and combats pathogens while retaining a memory of prior encounters. In the thymus, naïve T cells capable of recognizing specific antigens are generated through random gene rearrangement, ensuring a diverse immune repertoire. However, the production rate of naïve T cells declines with age, typically following an exponential or power-law function—a phenomenon known as thymic involution, which is often regarded as a deterioration of biological function (immunosenescence). In this paper, we propose a novel theory suggesting that thymic involution may represent an adaptive strategy. As individuals age, repeated exposure to diverse pathogens leads to the accumulation of memory T cells, thereby reducing the need for newly generated naïve T cells to combat infections. Moreover, naïve T cells can persist in the periphery and retain the capacity to initiate immune responses against novel antigens. Using Pontryagin’s Maximum Principle, we calculate the optimal schedule of naïve T cell production. The results show that the production rate peaks during a brief period shortly after birth, followed by an exponential decline throughout life, eventually reaching a phase in which naïve T cell production ceases. If peripheral naïve T cells decay very slowly, the optimal strategy may consist of producing all cohorts at birth, with no subsequent production.
Genetic diversity within a tree and alternative indexes for different evolutionary effects Yoh Iwasa, Sou Tomimoto, Akiko Satake Quantitative Plant Biology, 2024 Trees, living for centuries, accumulate somatic mutations in their growing trunks and branches, causing genetic divergence within a single tree. Stem cell lineages in a shoot apical meristem accumulate mutations independently and diverge from each other. In plants, somatic mutations can alter the genetic composition of reproductive organs and gametes, impacting future generations. To evaluate the genetic variation among a tree’s reproductive organs, we consider three indexes: mean pairwise phylogenetic distance ( $\\overline{D}$ ), phylogenetic diversity ( $PD$ ; sum of branch lengths in molecular phylogeny) and parent-offspring phylogenetic distance ( ${D}_{PO}$ ). The tissue architecture of trees facilitated the accumulation of somatic mutations, which have various evolutionary effects, including enhancing fitness under strong sib competition and intense host-pathogen interactions, efficiently eliminating deleterious mutations through epistasis and increasing genetic variance in the population. Choosing appropriate indexes for the genetic diversity of somatic mutations depends on the specific aspect of evolutionary influence being assessed.
Optimal seasonal schedule for the production of isoprene, a highly volatile biogenic VOC Yoh Iwasa, Rena Hayashi, Akiko Satake Scientific Reports, 2024 The leaves of many trees emit volatile organic compounds (abbreviated as BVOCs), which protect them from various damages, such as herbivory, pathogens, and heat stress. For example, isoprene is highly volatile and is known to enhance the resistance to heat stress. In this study, we analyze the optimal seasonal schedule for producing isoprene in leaves to mitigate damage. We assume that photosynthetic rate, heat stress, and the stress-suppressing effect of isoprene may vary throughout the season. We seek the seasonal schedule of isoprene production that maximizes the total net photosynthesis using Pontryagin’s maximum principle. The isoprene production rate is determined by the changing balance between the cost and benefit of enhanced leaf protection over time. If heat stress peaks in midsummer, isoprene production can reach its highest levels during the summer. However, if a large portion of leaves is lost due to heat stress in a short period, the optimal schedule involves peaking isoprene production after the peak of heat stress. Both high photosynthetic rate and high isoprene volatility in midsummer make the peak of isoprene production in spring. These results can be clearly understood by distinguishing immediate impacts and the impacts of future expectations.
Is Thymic Involution Truly a Deterioration or an Adaptation? Y Iwasa, R Hayashi, A Hara, K Matsuo Bulletin of Mathematical Biology 88 (2), 28 , 2026 2026
Human papillomavirus driving cervical cancer: A mathematical model with persistent infection, cancer progression, and spontaneous remission R Hayashi, A Hara, Y Iwasa Journal of Theoretical Biology 617 (112289), doi.org/10.1016/j.jtbi.2025.112289 , 2026 2026 Citations: 2
Seasonal scheduling of chemical defense in trees: An optimal-control approach: Y. Iwasa et al. Y Iwasa, R Hayashi, A Satake Japan Journal of Industrial and Applied Mathematics 42 (4), 1291-1307 , 2025 2025
Branching architecture affects genetic diversity within an individual tree S Tomimoto, Y Iwasa, A Satake Journal of Theoretical Biology 605 (112093), doi org/10.1016/j.jtbi.2025.112093 , 2025 2025 Citations: 5
Age-dependence of food allergy due to decreased supply of naive T cells Y Kotsubo, A Hara, R Hayashi, Y Iwasa Journal of Theoretical Biology 602 (112060), doi.org/10.1016/j.jtbi.2025.112060 , 2025 2025 Citations: 3
Optimal seasonal schedule for producing biogenic volatile organic compounds for tree defense Y Iwasa, R Hayashi, A Satake Journal of Theoretical Biology 596 (111986), doi.org/10.1016/j.jtbi.2024.111986 , 2025 2025 Citations: 4
Modeling innate immunity causing chronic inflammation and tissue damage K Matsuo, Y Iwasa Bulletin of Mathematical Biology 87 (art 34), doi.org/10.1007/s11538-024-01410-0 , 2025 2025 Citations: 5
Thymic involution as an adaptive schedule for combating diverse pathogens Y Iwasa, K Matsuo BioRxiv, 2024.12. 21.629868 , 2024 2024 Citations: 1
Genetic diversity within a tree and alternative indexes for different evolutionary effects Y Iwasa, S Tomimoto, A Satake Quantitative Plant Biology 5 (e11, 1-9.), https://dx.doi.org/10.1017/qpb.2024.9 , 2024 2024 Citations: 5
Optimal seasonal schedule for the production of isoprene, a highly volatile biogenic VOC Y Iwasa, R Hayashi, A Satake Scientific Reports 14 (12311), doi.org/10.1038/s41598-024-62975-3 , 2024 2024 Citations: 8
Human movement avoidance decisions during coronavirus disease 2019 in Japan R Omori, K Ito, S Kanemitsu, R Kimura, Y Iwasa Journal of Theoretical Biology 585, 111795 , 2024 2024 Citations: 3
Viral rebound occurrence immediately after drug discontinuation involving neither drug resistance nor latent reservoir R Hayashi, A Hara, Y Iwasa Journal of Theoretical Biology 582, 111767 , 2024 2024 Citations: 4
Multiple colonies of cancer involved in mutual suppression with the immune system K Matsuo, R Hayashi, Y Iwasa Journal of Theoretical Biology 572, 111577 , 2023 2023 Citations: 8
Temporal pattern of the emergence of a mutant virus escaping cross-immunity and stochastic extinction within a host. R Hayashi, Y Iwasa Bulletin of Mathematical Biology 85, 81 (doi: 10.1007/s11538-023-01184) , 2023 2023 Citations: 1
Mathematical modeling for developmental processes Y Iwasa Development Growth and Differentiation 2023, 1-10. doi: 10.1111/dgd.12856 , 2023 2023 Citations: 2
The genetic structure within a single tree is determined by the behavior of the stem cells in the meristem Y Iwasa, S Tomimoto, A Satake Genetics 223, iyad020 doi:10.1093/genetics/iyad020 , 2023 2023 Citations: 15
Waves of infection emerging from coupled social and epidemiological dynamics Y Iwasa, R Hayashi Journal of Theoretical Biology 558, 111366 , 2023 2023 Citations: 7
Theoretical studies of diverse sexual patterns in marine animals Y Iwasa, S Yamaguchi Proceedings of the Royal Society B: Biological Sciences 290 (1990) , 2023 2023 Citations: 1
On the role of eviction in group living sex changers Y Iwasa, S Yamaguchi Behavioral Ecology and Sociobiology 76 (4), 49 , 2022 2022 Citations: 3
Escaping stochastic extinction of mutant virus: temporal pattern of emergence of drug resistance within a host R Hayashi, S Iwami, Y Iwasa Journal of Theoretical Biology 537, 111029 , 2022 2022 Citations: 3
MOST CITED SCHOLAR PUBLICATIONS
Sexual selection M Andersson, Y Iwasa Trends in ecology & evolution 11 (2), 53-58 , 1996 1996 Citations: 17471
Influence of nonlinear incidence rates upon the behavior of SIRS epidemiological models W Liu, SA Levin, Y Iwasa Journal of mathematical biology 23 (2), 187-204 , 1986 1986 Citations: 1161
Dynamics of chronic myeloid leukaemia F Michor, TP Hughes, Y Iwasa, S Branford, NP Shah, CL Sawyers, ... Nature 435 (7046), 1267-1270 , 2005 2005 Citations: 1026
The evolution of costly mate preferences II. The “handicap” principle Y Iwasa, A Pomiankowski, S Nee Evolution 45 (6), 1431-1442 , 1991 1991 Citations: 979
Demographic theory for an open marine population with space‐limited recruitment J Roughgarden, Y Iwasa, C Baxter Ecology 66 (1), 54-67 , 1985 1985 Citations: 707
Prey distribution as a factor determining the choice of optimal foraging strategy Y Iwasa, M Higashi, N Yamamura The American Naturalist 117 (5), 710-723 , 1981 1981 Citations: 700
Dynamics of cancer progression F Michor, Y Iwasa, MA Nowak Nature reviews cancer 4 (3), 197-205 , 2004 2004 Citations: 679
How should we define goodness?—reputation dynamics in indirect reciprocity H Ohtsuki, Y Iwasa Journal of theoretical biology 231 (1), 107-120 , 2004 2004 Citations: 617
The leading eight: social norms that can maintain cooperation by indirect reciprocity H Ohtsuki, Y Iwasa Journal of theoretical biology 239 (4), 435-444 , 2006 2006 Citations: 612
The evolution of costly mate preferences I. Fisher and biased mutation A Pomiankowski, Y Iwasa, S Nee Evolution 45 (6), 1422-1430 , 1991 1991 Citations: 517
Indirect reciprocity provides only a narrow margin of efficiency for costly punishment H Ohtsuki, Y Iwasa, MA Nowak Nature 457 (7225), 79-82 , 2009 2009 Citations: 430
The evolution of cooperation in a lattice-structured population M Nakamaru, H Matsuda, Y Iwasa Journal of theoretical Biology 184 (1), 65-81 , 1997 1997 Citations: 401
Onymity promotes cooperation in social dilemma experiments Z Wang, M Jusup, RW Wang, L Shi, Y Iwasa, Y Moreno, J Kurths Science advances 3 (3), e1601444 , 2017 2017 Citations: 386
Theory of oviposition strategy of parasitoids. I. Effect of mortality and limited egg number Y Iwasa, Y Suzuki, H Matsuda Theoretical population biology 26 (2), 205-227 , 1984 1984 Citations: 364
The evolution of mate preferences for multiple sexual ornaments Y Iwasa, A Pomiankowski Evolution 48 (3), 853-867 , 1994 1994 Citations: 363
Shoot/root balance of plants: optimal growth of a system with many vegetative organs Y Iwasa, J Roughgarden Theoretical population biology 25 (1), 78-105 , 1984 1984 Citations: 341
Exploiting a cognitive bias promotes cooperation in social dilemma experiments Z Wang, M Jusup, L Shi, JH Lee, Y Iwasa, S Boccaletti Nature communications 9 (1), 2954 , 2018 2018 Citations: 339
Aggregation in model ecosystems. I. Perfect aggregation Y Iwasa, V Andreasen, S Levin Ecological Modelling 37 (3-4), 287-302 , 1987 1987 Citations: 323
Evolution of resistance during clonal expansion Y Iwasa, MA Nowak, F Michor Genetics 172 (4), 2557-2566 , 2006 2006 Citations: 306
Stochastic tunnels in evolutionary dynamics Y Iwasa, F Michor, MA Nowak Genetics 166 (3), 1571-1579 , 2004 2004 Citations: 306
