Biomolecular Information Gained through In Vitro Evolution on a Fitness Landscape in Sequence Space

Biological evolution at the molecular level is conceptually regarded as the genetic information gaining process. Analyzing the in vitro evolution process, which is a simplified Darwinian evolution under a well-controlled environment, we can clarify the concept of the information gaining process. This evolution process can be modeled as a hill-climbing or adaptive walk on a fitness landscape in sequence space. Through the hill-climbing process, the evolving biopolymer (as the adaptive walker) stores the following two aspects of information: one stems from the sequences converged in sequence space and the other stems from the fitness increment on the fitness landscape. In Eigen’s words, the former and latter are described as the “extent” and “content” of biological information, respectively [25]. In our approach, these two aspects can be interpreted based on the analogy between evolutionary dynamics and thermodynamics. Several studies introduced the concept of “free fitness” (which is analogous to free energy) as the Lyapunov function for evolution: Free fitness ≡ Fitness + Temperature − like parameter ×Entropy. Furthermore, we focus on the novel quantity of Fitness divided by \(\mbox{\it Temperature-like para\-meter}\), and regard this quantity as the content of information, while we regard Entropy as the extent of information. The quantity of Free fitness divided by Temperature-like parameter is a Lyapunov function of the evolution process, and then it should be called “biomolecular information”, which includes both aspects of information.