The Evolutionary Ontogenetic Program?
Generally speaking, the evolutionary’ ontogenetic research program is just beginning to take shape and is therefore is barely noticeable against the currently dominating cladistics based on the analysis of molecular data [Pavlinov 2019]. Its specificity is that it focuses on the evolutionarily interpreted disparity of ontogenetic patterns of multi-cellular organisms [Minelli 2015]. The basis for this is provided by a synthesis of the phylogenetics considered in its rather broadened sense, epigenetic typology, and the “evo-devo” concept (a now well-known abbreviation for evolutionary developmental biology). The concepts of dynamic archetype (phylocreod) and phylotype (phylotypic stage) mentioned above fit well into the context of this taxonomic theory, thus making a typological approach compatible with modern macroevolutionary theory [Lewens 2009b, Riegner 2013].
From a historical perspective, this theory goes back to the classical principle of trifold parallelism of the mid 19th century [Gould 1977]. Its fundamental novelty is incorporation of the evo-devo concept that focuses on the historical changes of the genetic mechanisms of regulation of ontogenesis [Minelli 2003, Laubichler and Maienschein 2008, Minelli and Pradeu 2014].
As can be seen, the evo-devo (or phylo-evo-devo) taxonomic theory and the respective research program are based on a rather rich biologically meaningful ontology, which distinguishes it positively from reductionist cladistics and molecular phylogenetics. This means another, newer version (along with biomorphics and evolutionary taxonomy) of the most recent biologization of systematics. At the same time, as far as phylogeny is considered one of the cornerstones of this program, it is possible to consider the latter as another branch of the phylogenetic program in its widest sense.
By focusing on the evolution of ontogenetic patterns and epigenetic mechanisms ensuring their historical stability and dynamics, this research program brings its own version of representing historical patterns of biodiversity and their respective classifications. The former can be represented by a phylo-ontogenetic tree, which is actually a phylogenetically interpreted “Baerian tree” (see Section 3.4 on the latter). This tree is transformed into a corresponding evo-devo classification in the same manner as the phylogenetic one, with its ranking scale being derived from a sequence of appearances of respective ontogenetic patterns in the evolution of multicellular organisms. The main characteristics of an evo-devo taxon become its specific ontogenetic pattern as a whole dynamic system, not reducible to any particular developmental stages [Orton 1955; Martynov 2011, 2012; Pavlinov 2013c; Minelli 2015]. All this provides biological systematics with a rich ontological basis and allows it to get rid of the overload reductionism brought in by the above-mentioned “new phylogenetics.”
From an epistemic viewpoint, the research program under consideration faces a serious problem caused by its rich natural ontology. The latter presumes that the elaboration of evo-devo classifications should be based on a joint exploration of two complexly interacting multifaceted dynamic systems of phylogeny and ontogeny [Rieppel 1989, 1990; Pavlinov 2013c]. In such a knotty cognitive situation, the above-mentioned NP-completeness problem [Garey and Johnson 1979] (see Section 5.7.1) becomes quite relevant.
It is evident that the evo-devo research program is not universal: its application is limited to groups of multicellular organisms with sufficiently developed ontogenetic cycles. Accordingly, many protists and apparently all prokaryotes appear to be outside the scope of its competence. However, this circumstance should hardly be considered a serious disadvantage: as emphasized repeatedly above, any research program in systematics and each particular taxonomic theory underlying it are inevitably local with regard to its applications.
At the moment, those classifications that realize the evo-devo taxonomic theory most consistently and, thus, belong to the program in question are very few. The reason is that detailed studies on diversity and evolution of the mechanisms of regulation of ontogenesis in animals and plants on a modern epigenetic basis are just beginning. Therefore, as always happens with new disciplines, they involve analyses of only a few model organisms. So, it seems premature to consider how actively this research program will be developing, how productive it may turn out to be for systematics, how serious the alterations of taxonomic classifications may be, and which particular alterations will occur. Among the main tasks to be solved by evo-devo taxonomic theory, to make the program in question more promising, seem to be the following: (a) elaboration of a calculus for assessment of the relative significance (weight) of the differences in molecular sequences and ontogenetic rearrangements; (b) elaboration of the unified ranking scale for the evo-devo classifications of different groups of organisms; and (c) development of an optimal way to combine vertical and horizontal interrelations between groups with different ontogenetic patterns to reflect best both their primitive (ancestral) and derived features.