Toward Developing Unifying Theories of Biology, Mathematics, and Society
Ryosuke Iritani
(Senior Research Scientist, iTHEMS)
Living organisms are immensely complex. Their complexity renders it challenging to understand organisms’ behaviors and evolutionary processes. Despite advances in genomic analysis starting to reveal more biological details, many mysteries remain unsolved. Mathematical biology aims to unravel these mysteries using mathematics. We spoke with Senior Researcher Ryosuke Iritani, who is conducting research in this field, about why he chose this field and found it so fascinating.
Affiliation and position are as of the interview date: November 2023
(Written and Photographed by Yoshitaka Arafune, science writer)
Pursuing a Path to Study Both Biology and Mathematics
"I first encountered a book on mathematical biology as an undergraduate student. I thought it was the perfect field where I could study both mathematics and biology," said Iritani.
In elementary school, Iritani collected insects as a hobby, and loved arithmetic. He would mentally multiply two-digit numbers from car license plates and calculate shopping totals, including tax, as a playful challenge.
At Kyoto University, he enrolled in the Faculty of Science, where he could study both biology and mathematics. Upon learning about the field of mathematical biology, Iritani contacted Professor Yoh Iwasa at Kyushu University, the author of the book he had encountered, and advanced his studies with his guidance.
"I received the advice to study a lot of mathematics while young, as learning new mathematics after obtaining a degree can be more challenging. Following that advice and making a habit of studying mathematics has been beneficial to me even now."
Creating Mathematically Significant Models in Biology
Knowing that differential equations and recurrence relations are fundamental in mathematical biology, Iritani focused on analytical studies during his undergraduate years. After graduation, he joined Professor Iwasa’s lab at Kyushu University, where he conducted research on migration of organisms.
"Migration of organisms involves exploring new habitats and is also related to kin selection theory, as migration helps avoid competition among siblings. During this time, I found kin selection fascinating and delved into this theory."
Professor Iwasa’s lab had a culture where doctoral students would spend a period of time at foreign research institutions. Iritani contacted international researchers who had written intriguing papers, which led him to spend time at the Centre d'Ecologie Fonctionnelle et Evolutive (CEFE, CNRS) in Montpellier, France, and at the University of Lausanne in Switzerland, advancing his research. “Around this time, I began to more deeply understand the appeal of mathematical biology,” recalls Iritani.
"One advice changed his mind. Instead of merely deriving equations using mathematical models, I should aim for biologically meaningful interpretations of these equations. Since then, I turned to arranging equations in a term-by-term basis, based on biological meanings. By deeply considering the connection between equations and biology, I found my research even more interesting."
Communicating Effectively with Both Biologists and Mathematicians
A significant turning point for Iritani came in 2018. At that time, he was a postdoctoral researcher at the University of California, Berkeley. Considering returning to Japan, he heard about an iTHEMS recruitment call, which he applied to. However, although he reached the interview stage in his first application, he was not finally selected. The next recruitment call came six months later, and he applied again, this time being successful.
"When the second recruitment call came, I was unsure whether to apply. However, a friend encouraged me to apply, and I made up my mind. What I realized through the two interviews was the importance of using mathematical language and concepts to clearly communicate with those knowledgeable in mathematics. In the second interview, I focused on not just discussing the biological meaning and phenomena but also clearly linking them with their mathematical expressions and significance. I learned the importance of speaking the language of both fields, and the two interviews were excellent learning experiences."
Changing the Way We See the World with Theory
Since joining iTHEMS, Iritani has met people from various different fields and has been greatly inspired. In his research, he constantly strives to communicate effectively with both mathematicians and biologists.
"Complex mathematical models with many parameters can predict biological phenomena, but their complexity can make them difficult to verify and interpret biologically. I aim to develop models as simple as possible for verification," Iritani explained. “For instance, in an epidemiological “SIR model,” which calculates how a disease spreads within a host population, incorporating sex requires finding the eigenvalues of a 6-by-6 matrix. However, by cleverly using symmetry and geometric properties, the analysis can be approximated to a 2-by-2 matrix, I found.”
Iritani describes the appeal of mathematical biology as follows: "In biology, many fundamental concepts have not yet been modeled. Mathematical biology conceptualizes biological phenomena through modeling. In this sense, I want to call it theoretical biology. When a concept is established, it helps understand how to interpret phenomena, changing the way we see the world. That's incredibly fascinating."
Iritani has focused his research on fundamental areas such as ecology and evolution, stemming from his love for basic mathematics and biology. However, through conversations with various researchers at iTHEMS, he has come to appreciate the importance of research connected to society.
"While continuing basic research, I also want to develop a theory that connects it with society. For example, conservation of biodiversity requires humans to create rules. By linking mathematical biology to society, I am keen on studying human behavioral principles, and social science theories. I hope to develop new theories that provide insights into a society where humans and nature can coexist."