The origin and early evolution of life in chemical composition space
The origin and early evolution of life in chemical composition space
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DOI：
10.1016/j.jtbi.2018.08.016
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发表时间：
2018-11-07
影响因子：
2
通讯作者：
Baum, David A.
中科院分区：
文献类型：
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作者：
Baum, David A.
生命可以被看作是一个局部化的化学系统，它位于一个亚稳态动力学吸引子状态的吸引盆中，与环境保持不平衡。为了探讨这一概念的含义，我介绍了一个抽象的坐标系，化学成分（CC空间），它总结了化学系统与大体积环境的平衡程度。系统的化学不平衡（CD）被定义为与物理空间的一个小区域的组成、像素和CC空间的原点之间的欧几里得距离成比例。这种模型意味着新的生命状态是通过局部化学浓度的偶然变化（“突变”）而产生的，这些变化导致化学系统在CC空间中移动并进入生命状态的吸引盆地。生命状态的吸引子包括一组自催化的化学物质，其基本（“基石”）物质的产生速率高于它们通过扩散而损失到环境中的速率，使得生命状态的空间增长是预期的。这一框架表明，新的生命状态最有可能形成在不同的物理相之间的界面，其中的关键物种的扩散率是绑在低扩散制度，而食品和废物产品受到更扩散的制度。一旦生命成核，例如在矿物表面上，它将倾向于生长并产生变异，这是由于找到替代生命状态的额外突变的结果。通过从一个生命状态跳到另一个生命状态，系统最终可以占据CC空间的区域，这些区域与环境的平衡太远，无法在单个突变步骤中出现。此外，我建议，在不同的表面相关的生命状态的持续和竞争的能力的变化可能会系统地有利于国家，具有较高的化学不平衡。该模型还提出了一个简单而可预测的路径，从表面相关的生命到细胞样的个性化。这个动力系统的理论框架提供了一个完整的观点的起源和生命的早期进化，并支持新的经验方法。(C)2018爱思唯尔有限公司版权所有
Life can be viewed as a localized chemical system that sits in the basin of attraction of a metastable dynamical attractor state that remains out of equilibrium with the environment. To explore the implications of this conception, I introduce an abstract coordinate system, chemical composition (CC Space), which summarizes the degree to which chemical systems are out of equilibrium with the bulk environment. A system's chemical disequilibrium (CD) is defined to be proportional to the Euclidean distance between the composition of a small region of physical space, a pixel, and the origin of CC space. Such a model implies that new living states arise through chance changes in local chemical concentration ("mutations") that cause chemical systems to move in CC space and enter the basin of attraction of a life state. The attractor of a life state comprises an autocatalytic set of chemicals whose essential ("keystone") species are produced at a higher rate than they are lost to the environment by diffusion, such that spatial growth of the life state is expected. This framework suggests that new life states are most likely to form at the interface between different physical phases, where the rate of diffusion of keystone species is tied to the low-diffusion regime, whereas food and waste products are subject to the more diffusive regime. Once life nucleates, for example on a mineral surface, it will tend to grow and generate variants as a result of additional mutations that find alternative life states. By jumping from life state to life state, systems can eventually occupy areas of CC space that are too far out of equilibrium with the environment to ever arise in a single mutational step. Furthermore, I propose that variation in the capacity of different surface associated life states to persist and compete may systematically favor states that have higher chemical disequilibrium. The model also suggests a simple and predictable path from surface-associated life to cell-like individuation. This dynamical systems theoretical framework provides an integrated view of the origin and early evolution of life and supports novel empirical approaches. (C) 2018 Elsevier Ltd. All rights reserved.