Design principle of optimal biological systems

Biology does not seem to have as unified theories as physics or chemistry. Nevertheless, as all organisms participated natural selection with no exception, they optimally adapt to the environment through the evolution. Therefore, their existence and necessity can be accounted for by the notion of optimality. We are trying to answer many biological riddles by mathematical optimization. Specifically, we studied an optimal design of circadian clocks (24 h biological clock). Many terrestrial species from bacteria to humans acquired circadian oscillatory systems to increase chances of survival. In order to maintain the endogenous clock, two properties are necessary: regularity, to keep time precisely and entrainability to synchronize the internal time to the environmental cycle. However, these two requirements are trade-off factors and it is difficult to satisfy them simultaneously. By using mathematical optimization, we found for the first time that all existing circadian clocks are near optimal and that many inherent properties of circadian clocks can be explained by the optimality.

生物には，物理学にあるような統一的な理論があまりないように思えます．しかし，実際には現存する生物は例外なく「進化」という過程を経ているため，全ての生物システムは環境に対して高度に最適化されています．生物システムには多くの「Why?」が存在しますが，その問いに対する答えを最適化の観点から導き出すことが出来るのではないか，というのが研究テーマの一つです．具体的には，体内時計と呼ばれる生体振動子の最適設計原理を明らかにしました．バクテリアから人に至るまで，ほとんどの生物には24時間周期の体内時計が備わっています．「時計」であるため，正確に時間を刻む必要があると同時に，外界の時間に同期する能力も必要です．これらはトレードオフな要素なため，最適に二つを満たすことは制約付きの最適化に相当します．数理最適化によって，現存の全ての体内時計が最適値に近いことを世界で初めて明らかにしました．