Sharov Alexei A
National Institute on Aging, Genetics Laboratory, 251 Bayview Blvd., Baltimore, MD 21224, USA.
Biosystems. 2014 Apr 22;120C:21-30. doi: 10.1016/j.biosystems.2014.04.005.
Natural selection is traditionally viewed as a leading factor of evolution, whereas variation is assumed to be random and non-directional. Any order in variation is attributed to epigenetic or developmental constraints that can hinder the action of natural selection. In contrast I consider the positive role of epigenetic mechanisms in evolution because they provide organisms with opportunities for rapid adaptive change. Because the term "constraint" has negative connotations, I use the term "regulated variation" to emphasize the adaptive nature of phenotypic variation, which helps populations and species to survive and evolve in changing environments. The capacity to produce regulated variation is a phenotypic property, which is not described in the genome. Instead, the genome acts as a switchboard, where mostly random mutations switch "on" or "off" preexisting functional capacities of organism components. Thus, there are two channels of heredity: informational (genomic) and structure-functional (phenotypic). Functional capacities of organisms most likely emerged in a chain of modifications and combinations of more simple ancestral functions. The role of DNA has been to keep records of these changes (without describing the result) so that they can be reproduced in the following generations. Evolutionary opportunities include adjustments of individual functions, multitasking, connection between various components of an organism, and interaction between organisms. The adaptive nature of regulated variation can be explained by the differential success of lineages in macro-evolution. Lineages with more advantageous patterns of regulated variation are likely to produce more species and secure more resources (i.e., long-term lineage selection).
传统上，自然选择被视为进化的主要因素，而变异则被认为是随机且无方向的。变异中的任何秩序都归因于表观遗传或发育限制，这些限制可能会阻碍自然选择的作用。相比之下，我认为表观遗传机制在进化中具有积极作用，因为它们为生物体提供了快速适应性变化的机会。由于“限制”一词具有负面含义，我使用“调控变异”一词来强调表型变异的适应性本质，这有助于种群和物种在不断变化的环境中生存和进化。产生调控变异的能力是一种表型特性，在基因组中并未描述。相反，基因组就像一个总机，大多数随机突变在这里“开启”或“关闭”生物体组成部分预先存在的功能能力。因此，存在两种遗传渠道：信息性（基因组）和结构功能性（表型）。生物体的功能能力很可能是在一系列更简单的祖先功能的修饰和组合中出现的。DNA的作用是记录这些变化（而不描述结果），以便它们能够在后代中重现。进化机会包括个体功能的调整、多任务处理、生物体各个组成部分之间的联系以及生物体之间的相互作用。调控变异的适应性本质可以通过宏观进化中谱系的不同成功来解释。具有更有利调控变异模式的谱系可能会产生更多物种并获取更多资源（即长期谱系选择）。
