Comparative biology builds up systematic knowledge of the diversity of life, across evolutionary lineages and levels of organization, starting with evidence from a sparse sample of model organisms. In developmental biology, a key obstacle to the growth of comparative approaches is that the concept of homology is not very well defined for levels of organization that are intermediate between individual genes and morphological characters. In this paper, we investigate what it means for ontogenetic processes to be homologous, focusing specifically on the examples of insect segmentation and vertebrate somitogenesis. These processes can be homologous without homology of the underlying genes or gene networks, since the latter can diverge over evolutionary time, while the dynamics of the process remain the same. Ontogenetic processes like these therefore constitute a dissociable level and distinctive unit of comparison requiring their own specific criteria of homology. In addition, such processes are typically complex and nonlinear, such that their rigorous description and comparison requires not only observation and experimentation, but also dynamical modelling. We propose six criteria of process homology, combining recognized indicators (sameness of parts, morphological outcome and topological position) with novel ones derived from dynamical systems modelling (sameness of dynamical properties, dynamical complexity and evidence for transitional forms). We show how these criteria apply to animal segmentation and other ontogenetic processes. We conclude by situating our proposed dynamical framework for homology of process in relation to similar research programmes, such as process structuralism and developmental approaches to morphological homology.

比较生物学从模型生物的稀疏样本中获得证据，建立了关于生命多样性、跨越进化谱系和组织层次的系统知识。在发育生物学中，比较方法发展的一个主要障碍是，对于介于个体基因和形态特征之间的组织水平，同源性的概念没有得到很好的定义。在本文中，我们研究了个体发生过程同源的含义，特别关注昆虫分节和脊椎动物体细胞发生的例子。这些过程可以是同源的，而无需底层基因或基因网络的同源性，因为后者可能随着进化时间的推移而出现分歧，而过程的动态保持不变。因此，像这样的个体发生过程构成了一个可分离的水平和独特的比较单位，需要它们自己特定的同源性标准。此外，此类过程通常是复杂和非线性的，因此对其进行严格的描述和比较不仅需要观察和实验，还需要动态建模。我们提出了过程同源性的六个标准，将公认的指标（部件的相同性、形态结果和拓扑位置）与动力系统建模中衍生的新颖指标（动力特性的相同性、动力复杂性和过渡形式的证据）结合起来。我们展示了这些标准如何应用于动物分割和其他个体发育过程。最后，我们将我们提出的过程同源性动态框架与类似的研究项目（例如过程结构主义和形态同源性的发展方法）联系起来。