The forces driving regression of biologically functionless traits remain disputed. There is ongoing debate regarding whether selection, as opposed to disuse and neutral mutations, is involved in this process. Cave species are of particular relevance for study in this regard because in continuous darkness all traits that depend on information from light, such as eyes, dark pigmentation and certain behaviours, abruptly lose their function. Recently, strong selection driving reduction has again been proposed, which relied on modelling analyses based on assumptions such as immigration of surface alleles into the cave forms or no fitness difference existing between Astyanax surface and cave fish. The validity of these assumptions, often applied to reject neutral processes in functionless traits, is questioned in this review. Morphological variation in a trait resulting from genetic variability is typical of biologically functionless traits and is particularly notable in phylogenetically young cave species. It is the most evident indicator of loss of selection, which normally enforces uniformity to guarantee optimal functionality. Phenotypic and genotypic variability in Astyanax cave fish eyes does not derive from genetic introgression by the surface form, but from regressive mutations not being eliminated by selection. This matches well with the principles of Kimura’s neutral theory of molecular evolution.

中文翻译：

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选择在洞穴鱼类失明进化中的作用

驱使无生物学功能的性状退化的力量仍然存在争议。关于选择，而不是废品和中性突变，是否参与了这一过程，目前正在进行辩论。洞穴物种在这方面与研究特别相关，因为在连续黑暗中，所有依赖于光信息的特征（例如眼睛，深色色素和某些行为）突然失去其功能。最近，再次提出了强选择驱动降低的方法，该方法基于模型分析，该模型分析基于以下假设：表面等位基因迁移到洞穴形式中，或者在Astyanax之间不存在适应性差异表面和洞穴鱼。在这篇评论中，人们常常质疑这些假设的有效性，这些假设通常用于拒绝无功能性状的中性过程。由遗传变异引起的性状的形态变异是生物学上无功能性状的典型特征，在系统发育上较年轻的洞穴物种中尤为明显。它是丢失选择的最明显指标，通常会要求一致性以保证最佳功能。Astyanax洞穴鱼眼中的表型和基因型变异性并非源于表面形态的基因渗入，而是源于通过选择无法消除的回归突变。这与Kimura的分子进化中性理论的原理非常吻合。