Motility often plays a decisive role in the survival of species. Five systems of motility have been studied in depth: those propelled by bacterial flagella, eukaryotic actin polymerization and the eukaryotic motor proteins myosin, kinesin and dynein. However, many organisms exhibit surprisingly diverse motilities, and advances in genomics, molecular biology and imaging have showed that those motilities have inherently independent mechanisms. This makes defining the breadth of motility nontrivial, because novel motilities may be driven by unknown mechanisms. Here, we classify the known motilities based on the unique classes of movement-producing protein architectures. Based on this criterion, the current total of independent motility systems stands at 18 types. In this perspective, we discuss these modes of motility relative to the latest phylogenetic Tree of Life and propose a history of motility. During the ~4 billion years since the emergence of life, motility arose in Bacteria with flagella and pili, and in Archaea with archaella. Newer modes of motility became possible in Eukarya with changes to the cell envelope. Presence or absence of a peptidoglycan layer, the acquisition of robust membrane dynamics, the enlargement of cells and environmental opportunities likely provided the context for the (co)evolution of novel types of motility.

中文翻译：

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运动树-生命树中运动系统的拟议历史。

运动性通常在物种的生存中起决定性作用。已对5种运动系统进行了深入研究：细菌鞭毛，真核肌动蛋白聚合以及真核运动蛋白肌球蛋白，驱动蛋白和动力蛋白所推动的那些系统。但是，许多生物体表现出惊人的多样性，并且基因组学，分子生物学和成像技术的进步表明，这些本质上具有独立的机制。这使得确定运动的广度变得不容易，因为新颖的运动可能是由未知机制驱动的。在这里，我们根据产生运动的蛋白质结构的独特类别对已知的功能进行分类。基于此标准，当前独立运动系统的总数为18种。从这个角度来看，我们讨论了相对于最新的系统进化生命树的这些运动方式，并提出了运动史。自生命出现以来的约40亿年间，细菌与鞭毛和菌毛一起生长，而古细菌与古细菌一起发生运动。随着细胞包膜的改变，在Eukarya中出现了新的运动模式。肽聚糖层的存在与否，稳健的膜动力学的获得，细胞的扩大和环境机会可能为新型运动的（共）进化提供了背景。