Gagrani Praful, Baum David
Institute of Industrial Science, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505 Japan.
University of Wisconsin-Madison, Wisconsin Institute for Discovery, Madison, Wisconsin 53715, USA.
Phys Rev E. 2025 Jun;111(6-1):064403. doi: 10.1103/PhysRevE.111.064403.
While modern physics and biology satisfactorily explain the passage from the Big Bang to the formation of Earth and the first cells to present-day life, respectively, the origins of biochemical life still remain an open question. Since life, as we know it, requires extremely long genetic polymers, any answer to the question must explain how an evolving system of polymers of ever-increasing length could come about on a planet that otherwise consisted only of small molecular building blocks. In this work we show that, under realistic constraints, an abstract polymer model can exhibit dynamics such that attractors in the polymer population space with a higher average polymer length are also more probable. We generalize from the model and formalize the notions of complexity and evolution for chemical reaction networks with multiple attractors. The complexity of a species is defined as the minimum number of reactions needed to produce it from a set of building blocks, which in turn is used to define a measure of complexity for an attractor. A transition between attractors is considered to be a progressive evolution if the attractor with the higher probability also has a higher complexity. In an environment where only monomers are readily available, the attractor with a higher average polymer length is more complex. Thus, by this criterion, our abstract polymer model can exhibit progressive evolution for a range of thermodynamically plausible rate constants. We also formalize criteria for open-ended and historically contingent evolution and explain the role of autocatalysis in obtaining them. Our work provides a basis for searching for prebiotically plausible scenarios in which long polymers can emerge and yield populations with even longer polymers. Additionally, the existence of features like history dependence and open endedness support the view that the path from chemistry to biology was one of gradual complexification rather than an instantaneous origin of life.
虽然现代物理学和生物学分别令人满意地解释了从大爆炸到地球形成以及从最初的细胞到当今生命的过程，但生物化学生命的起源仍然是一个悬而未决的问题。我们所知的生命需要极长的遗传聚合物，因此对于这个问题的任何答案都必须解释在一个原本只由小分子构建块组成的行星上，一个聚合物长度不断增加的进化系统是如何产生的。在这项工作中，我们表明，在现实的限制条件下，一个抽象的聚合物模型可以展现出这样的动力学特性：聚合物种群空间中平均聚合物长度更高的吸引子也更有可能出现。我们从该模型进行推广，并对具有多个吸引子的化学反应网络的复杂性和进化概念进行了形式化定义。一个物种的复杂性被定义为从一组构建块产生该物种所需的最少反应数，进而用它来定义一个吸引子的复杂性度量。如果具有更高概率的吸引子也具有更高的复杂性，那么吸引子之间的转变就被认为是一种渐进进化。在一个只有单体容易获得的环境中，平均聚合物长度更高的吸引子更复杂。因此，按照这个标准，我们的抽象聚合物模型在一系列热力学上合理的速率常数范围内可以展现出渐进进化。我们还对开放式和历史偶然进化的标准进行了形式化定义，并解释了自催化在实现这些标准中的作用。我们的工作为寻找在其中长聚合物能够出现并产生聚合物长度更长的种群的益生元似然情景提供了基础。此外，历史依赖性和开放式等特征的存在支持了这样一种观点，即从化学到生物学的路径是一个逐渐复杂化的过程，而不是生命的瞬间起源。
