Fitness contribution alone should not be the criterion of ‘function’ in molecular biology and genomics. Disagreement over the use of ‘function’ in molecular biology and genomics is still with us, almost eight years after publicity surrounding the Encyclopedia of DNA Elements project claimed that 80.4% of the human genome comprises “functional elements”. Recent approaches attempt to resolve or reformulate this debate by redefining genomic ‘function’ in terms of current fitness contribution. In its favour, this redefinition for the genomic context is in apparent conformity with predominant experimental practices, especially in biomedical research, and with ascription of function by selective maintenance. We argue against approaches of this kind, however, on the grounds that they could be seen as non-Darwinian, and fail to properly account for the diversity of non-adaptive processes involved in the origin and maintenance of genomic complexity. We examine cases of molecular and organismal complexity that arise neutrally, showing how purifying selection maintains non-adaptive genomic complexity. Rather than lumping different sorts of genomic complexity together by defining ‘function’ as fitness contribution, we argue that it is best to separate the heterogeneous contributions of preaptation, exaptation and adaptation to the historical processes of origin and maintenance for complex features.

仅健身贡献不应该成为分子生物学和基因组学中“功能”的标准。关于在分子生物学和基因组学中使用“功能”的分歧仍然存在，在围绕 DNA 元素百科全书项目的宣传声称 80.4% 的人类基因组包含“功能元素”近八年后。最近的方法试图通过根据当前的健康贡献重新定义基因组“功能”来解决或重新制定这一争论。对其有利的是，对基因组背景的重新定义显然符合主要的实验实践，特别是在生物医学研究中，并且通过选择性维护来赋予功能。然而，我们反对这种方法，理由是它们可以被视为非达尔文主义的，并且未能正确解释与基因组复杂性的起源和维持有关的非适应性过程的多样性。我们检查了中性出现的分子和有机体复杂性的案例，展示了纯化选择如何保持非适应性基因组复杂性。与其通过将“功能”定义为适应度贡献将不同类型的基因组复杂性混为一谈，我们认为最好将预适应、扩展和适应复杂特征的起源和维护的历史过程的异质贡献分开。