The increasing maximal hierarchical complexity of organisms is one of the best-supported macroevolutionary trends. The nature and causes of this trend, as well as several accompanying macroevolutionary phenomena are, however, still unclear. In this theoretical article, we propose that the cause of this trend could be the increasing pressure of species selection, which results from the gradual decrease of (macro)evolutionary potential (i.e. the probability of producing major evolutionary innovations). As follows from the Theory of Frozen Evolution, this process is an inevitable consequence of the sorting of genes, traits, and their integrated groups (modules) based on their contextually dependent stability. In turn, this causes effectively unchangeable elements of genetic architecture to accumulate during the existence of evolutionary lineages. Although (macro)evolutionary potential can be partially restored by several processes, a profound restoration of (macro)evolutionary potential is probably possible only by means of a transition to a higher level of hierarchical complexity. However, the accumulation of contextually more stable elements continues even on this higher level. This leads to the integration of the modular character of composite organisms and a repeated pressure to increase the level of hierarchical complexity. Our model explains all components of McShea’s “Evolutionary Syndrome,” i.e. the trend of increasing the hierarchical complexity of organisms, the growth of variability among elements on the immediately lower level, and their gradual machinification. This pattern should be characteristic of sexual eukaryotes and especially their complex representatives. Our model also sheds new light on several related macroevolutionary phenomena, such as the gradual acceleration of the trend or the striking difference between pre-Neoproterozoic and Phanerozoic evolution.

中文翻译：

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美德的必然性：性进化论的等级复杂性增加是其（宏观）进化潜能下降的必然结果吗？

有机体最大的层次复杂性的增加是最受支持的宏观进化趋势之一。然而，这种趋势的性质和原因，以及一些伴随的宏观进化现象仍然不清楚。在这篇理论文章中，我们认为，造成这种趋势的原因可能是物种选择压力的增加，这是由于（宏观）进化潜能（即产生重大进化创新的可能性）逐渐降低所致。正如《冻结进化论》所述，这一过程是基因，性状及其整合基团（模块）基于上下文相关稳定性的排序的必然结果。反过来，这会导致遗传结构中不可改变的有效元素在进化世系的存在期间积累。尽管可以通过几个过程部分地恢复（宏观）进化潜力，但是只有通过过渡到更高层次的层次复杂性，才能（深度）恢复（宏观）进化潜力。但是，即使在更高的级别上，上下文上更稳定的元素的累积仍在继续。这导致了复合生物的模块化特征的整合以及不断增加的压力，以增加分级复杂性的水平。我们的模型解释了McShea的“进化综合症”的所有组成部分，即，生物体的层次复杂性不断提高的趋势，紧邻较低层次的元素之间的变异性的增长以及它们的逐渐机械化。这种模式应该是性真核生物特别是其复杂代表的特征。