Reconstructing serial homology with a special emphasis on the nature of limbs in vertebrates and with references to Cruveilhier, Wyman, Belogolowy, and Balinsky.

This analysis was inspired by the recent paper by Siomava et al. (2020) who attempted to deconstruct the serial homology concept, but retain the special homology. The criticism against this attempt is presented based on reconsideration of the original Owen's trinitarian concept of the general, serial, and special homology, and on a number of evidence on the vertebrate limbs serial homologies and on the vertebrate occiput special homologies which are currently missed by the morphologist community. The research of Belogolowy (1911) proved that the concept of special homology can be deconstructed with the same reasoning as suggested by Siomava et al. (2020) against the serial homology concept. It is argued that the deconstruction attempts come from wrong expectations in respect of homology. It is argued, that, due to developmental singularities, such as the zygote, or spore, or bud (in vegetative reproduction), the true homogeny is possible for genes only. The organs do not arise from organs, and therefore their genetic basis, and hence homology, can be changed in the developmental singularities. Thus, the morphological homology is not static. It can be acquired and it can evolve. Genetically, the evolution of morphological homologies can be thought of as a succession of co-options. The evidence for a succession of serial homologies in vertebrate limbs is suggested. It is argued that homology and analogy have a sense only in relation to each other. When two correspondences between two organs exist simultaneously, the older (deeper in time) is homology, and the newer (more superficial) is analogy. In this conceptual framework of evolvable homology, neither of the three Owen's types of homology can be abandoned. Three respective types of analogy should be added-the general analogy, the serial analogy, and the special analogy.