Adolf Naef (1883–1949), systematic morphology and phylogenetics

Several authors have highlighted methodological similarities between Naef’s systematic morphology and Hennig’s phylogenetic systematics. Whereas this may indicate an influence of Naef on Hennig, the relevant issues – such as the principle of generality in character analysis and the threefold parallelism of classification, ontogeny and the Fossil Record – reach back beyond Naef and Hennig and were widely discussed in the German systematics literature of the late 19th and early 20th Century. The same is true of conceptual issues, such as the discussion of the principle of monophyly, which was first introduced by Haeckel in 1866 ( Rieppel 2011b , J Zool Syst Evol Res 49 :1). In spite of methodological and conceptual agreements, Naef’s systematic morphology differed fundamentally from Hennig’s phylogenetic systematics. Naef emphasized the role of unbiased observation and the immediate acquaintance of the investigator with the phenomena given in nature as the basis of natural science in general, and of his hierarchy of types in particular. From the hierarchy of types, Naef derived through conceptual‐logical analysis the natural system, which above the species level forms a nested hierarchy of intensionally defined classes, denoted by general names. The historical‐causal interpretation of the hierarchy of types in turn offers insight into the hypothetical reality of phylogeny. Hennig in contrast denied the possibility of theory‐free observation, indeed of assumption‐free science in general, and on that basis put metaphysical issues above epistemology. Tying individuality to spatiotemporal location, historicity and causality, Hennig took not only species (as did Naef) but also supraspecific monophyletic taxa as individuals, denoted by proper names. From the species up, the phylogenetic system thus becomes a nested hierarchy of complex wholes of increasing degrees of complexity. Diagnostic characters of species or higher taxa can then no longer define classes (as in Naef’s natural system) but are thought to indirectly indicate the phylogenetic relations on which alone the phylogenetic system is to be based.     

Willi Hennig’s dichotomization of nature

Two formal assumptions implied in Willi Hennig’s “phylogenetic systematics” were repeatedly criticized for not being biologically grounded. The first is that speciation is always dichotomous; the second is that the stem‐species always goes extinct when its lineage splits into two daughter species. This paper traces the theoretical roots of Hennig’s “principle of dichotomy”. While often considered merely a methodological principle, Hennig’s realist perspective required him to ground the “principle of dichotomy” ontologically in speciation. As a methodological principle, the adherence to a strictly dichotomously structured phylogenetic system allowed Hennig to be unequivocal in character analysis and precise in the rendition of phylogenetic relationships. The ontological grounding of the “principle of dichotomy” in speciation remains controversial, however. This has implications for the application of techniques of phylogeny reconstruction to populations of bisexually reproducing organisms (phylogeography). Beyond that, the “principle of dichotomy” has triggered an intensive debate with respect to phylogeny reconstruction at the prokaryote level. © The Willi Hennig Society 2010.     

Grundsätze der phylogenetischen Systematik (Eine praxisorientierte Übersicht)

The essential elements of phylogenetic systematics in the sense of Hennig are emphasized: The search for synapomorphies based on a special method of comparative morphology, and the aim of an exclusive use of synapomorphies for kinship proof and the basis of systematics. Special aspects of comparative morphology are: “Directed comparisons” steady reciprocal reflection between comparative morphological result and the system methodical efforts for the realization of distinctive details, comprehensive documentation and functional interpretation. This is equally true for recent and fossil forms. Most suitable for the method (in the sense defined above) are groups with numerous differentiated morphological characters, which can also be preserved in the fossil state. The less this is the case the less is the chance for achieving necessary numbers of well proven synapomorphies. Even so, it is not permitted—for those who want to perform phylogenetic systematics in the sense of Hennig—to use convergences, parallelisms or symplesiomorphies in the sense of “synapomorphies” as phylogenetic arguments for kinship relations. Numerous examples and diagrams demonstrate the methodological proceeding, and differences towards other methods of phylogenetical reconstruction and interpretation. Special attention is paid to direct and indirect conclusions drawn from fossils: Time of origin of characters, stem groups and *groups; predictions concerning the appearance (set of characters) of fossils and simultaneous existence of “neighbour groups” (sister groups, and more distantly related taxa).     

Convergence and parallelism: is a new life ahead of old concepts?

In comparative biology, character observations initially separate similar and dissimilar characters. Only similar characters are considered for phylogeny reconstruction; their homology is attested in a two‐step process, firstly a priori of phylogeny reconstruction by accurate similarity statements, and secondly a posteriori of phylogeny analysis by congruence with other characters. Any pattern of non‐homology is then a homoplasy, commonly, but vaguely, associated with “convergence”. In this logical scheme, there is no way to analyze characters which look similar, but cannot meet usual criteria for homology statements, i.e., false similarity detected a priori of phylogenetic analysis, even though such characters may represent evolutionarily significant patterns of character transformations. Because phylogenies are not only patterns of taxa relationships but also references for evolutionary studies, we propose to redefine the traditional concepts of parallelism and convergence to associate patterns of non‐homology with explicit theoretical contexts: homoplasy is restricted to non‐similarity detected a posteriori of phylogeny analysis and related to parallelism; non‐similarity detected a priori of phylogenetic analysis and necessarily described by different characters would then correspond to a convergence event s. str. We propose to characterize these characters as heterologous (heterology). Heterology and homoplasy correspond to different non‐similarity patterns and processes; they are also associated with different patterns of taxa relationships: homoplasy can occur only in non‐sister group taxa; no such limit exists for heterology. The usefulness of these terms and concepts is illustrated with patterns of acoustic evolution in ensiferan insects. © The Willi Hennig Society 2005.     

Homology and errors

A recent review of the homology concept in cladistics is critiqued in light of the historical literature. Homology as a notion relevant to the recognition of clades remains equivalent to synapomorphy. Some symplesiomorphies are “homologies” inasmuch as they represent synapomorphies of more inclusive taxa; others are complementary character states that do not imply any shared evolutionary history among the taxa that exhibit the state. Undirected character‐state change (as characters optimized on an unrooted tree) is a necessary but not sufficient test of homology, because the addition of a root may alter parsimonious reconstructions. Primary and secondary homology are defended as realistic representations of discovery procedures in comparative biology, recognizable even in Direct Optimization. The epistemological relationship between homology as evidence and common ancestry as explanation is again emphasized. An alternative definition of homology is proposed. © The Willi Hennig Society 2012.     

PHYLOGENETIC SELECTION OF A RESOURCE: A NEW USE FOR CLADISTICS

A phylogenetic model for the selection of commercial resources using the cladistic method is proposed. The group selected as an example was the marine agarophyte red algal genus Gracilaria Greville. We suggest the use of the cladistic principle of evolutionary transformational series in order to test the quality of agars instead of the assay‐herror traditional method that consumes time and budget. If we asume that the “good quality of agar” in extant taxa is a sinapomorphic character (but not a reliable taxonomic one), then taxa included in the same monophiletic clade in which the species with “good quality of agar” are, has a high evolutionary posibility to share that character. In order to do this we have to incorporate to the set of available specific characters, those of the taxa actually used as a agar source but not present in the area under scope. A complete set of the basic cladistic data required for run the most popular program currently in use (PAUP) are provided. We applied the model to the Mexican Atlantic species and found that, using Gracilaria chilensis and G. cornea as “indicator taxa,” and found Mexican populations of G. crassissima, G. caudata, G. cervicornis and Gracilariopsis lemaneiformis are candidates for a study of yield and agar properties.     

Impact of increased character sampling on the phylogeny of Cetartiodactyla (Mammalia): combined analysis including fossils

The phylogenetic position of Cetacea (whales, dolphins and porpoises) is an important exemplar problem for combined data parsimony analyses because the clade is ancient and includes many well‐known and relatively complete fossil species. We combined data for 71 terminal taxa (43 extinct/28 extant) to test where Cetacea fits within Cetartiodactyla, and where various fossil hoofed mammals (e.g., ?entelodonts, “?anthracotheriids” and ?mesonychians) are positioned. We scored 635 phenotypic characters (osteology, dentition, soft tissue, behavior), approximately three times the number of characters in the last major analysis of this clade, and combined these with > 40 000 molecular characters, including new data from 10 genes. The analysis supported a topology consistent with the majority of recently published molecular studies. Cetacea was the extant sister taxon of Hippopotamidae, followed successively by Ruminantia, Suina and Camelidae. Several extinct taxa were phylogenetically unstable, upsetting resolution of the strict consensus and limiting branch support, but the positions of several key fossils were consistently resolved. The wholly extinct ?Mesonychia was more closely related to Cetacea than was any “artiodactylan.”“?Anthracotheriids” were paraphyletic, and, with the exception of one species, were more closely related to Hippopotamidae than to any other living taxon. The total evidence analysis overturned a highly nested position for Moschus supported by molecular data alone. The character partition that could be scored for the fossil taxa (osteological and dental characters) included more informative characters than most molecular partitions in our analysis, and had the fewest missing data. The osteological–dental data alone, however, did not support inclusion of cetaceans within crown “Artiodactyla.” Recently discovered ankle bones from fossil whales reinforced the monophyly of Cetartiodactyla but provided no particular evidence of derived similarities between hippopotamids and fossil cetaceans that were not shared with other “artiodactylans”. © The Willi Hennig Society 2007.     

The role of wood anatomy in phylogeny reconstruction of Ericales

The systematic significance of wood anatomical characters within Ericales is evaluated using separate and combined parsimony analyses including 23 wood characters and 3945 informative molecular characters. Analyses of wood features alone result in poorly resolved and conflicting topologies. However, when pedomorphic character states are coded as inapplicable, the combined bootstrap topology results in an increase of resolution and support at most deeper nodes compared with the molecular analyses. This suggests that phylogenetic information from the limited number of morphological characters is not completely swamped by an overwhelming amount of molecular data. Based on the morphology of vessels and fibers, and the distribution of axial parenchyma, two major wood types can be distinguished within Ericales: (i) a “primitive” type, nearly identical to the wood structure in the more basal outgroup Cornales, which is likely to have persisted in one major clade, and (ii) a “derived” type that must have evolved in at least two separate evolutionary lines. The occurrence of the first type is strongly correlated with shrubs to small trees growing in cold temperate or tropical montane regions, while the second type is common in tall trees of tropical lowlands. This favors the inclusion of ecologically adaptive features in phylogeny reconstruction. © The Willi Hennig Society 2006.     

Homology: Homeostatic Property Cluster Kinds in Systematics and Evolution

Taxa and homologues can in our view be construed both as kinds and as individuals. However, the conceptualization of taxa as natural kinds in the sense of homeostatic property cluster kinds has been criticized by some systematists, as it seems that even such kinds cannot evolve due to their being homeostatic. We reply by arguing that the treatment of transformational and taxic homologies, respectively, as dynamic and static aspects of the same homeostatic property cluster kind represents a good perspective for supporting the conceptualization of taxa as kinds. The focus on a phenomenon of homology based on causal processes (e.g., connectivity, activity-function, genetics, inheritance, and modularity) and implying relationship with modification yields a notion of natural kinds conforming to the phylogenetic-evolutionary framework. Nevertheless, homeostatic property cluster kinds in taxonomic and evolutionary practice must be rooted in the primacy of epistemological classification (homology as observational properties) over metaphysical generalization (series of transformation and common ancestry as unobservational processes). The perspective of individuating characters exclusively by historical-transformational independence instead of their developmental, structural, and functional independence fails to yield a sufficient practical interplay between theory and observation. Purely ontological and ostensional perspectives in evolution and phylogeny (e.g., an ideographic character concept and PhyloCode’s ‘individualism’ of clades) may be pragmatically contested in the case of urgent issues in biodiversity research, conservation, and systematics.     

以演化时间为新增指标构建真菌分类系统

随着分子系统发育研究的普及,真菌各分类类群逐渐被修订为单系发生类群,通常结合形态学特征为代表的表型特征("单系+表型特征")对不同的分类等级命名是最为普遍的方法.历史上存在的大量多系名称被逐步修订、补充和完善,各个不同等级类群的分类系统变得更加合理、客观和趋于自然,这是分类学进程中巨大的进步.然而系统发育重建所揭示的单...     

Othenio Abel (1875–1946) and “the phylogeny of the parts”1

The reconstruction of the evolutionary history of animal phyla was an integral part of Othenio Abel’s paleobiology (paleozoology). Abel took issue with those phylogeneticists who, following the lead of Haeckel, would draw up phylogenetic trees on the basis of transformation series of singular characters considered to be of particular importance. Abel highlighted Louis Dollo’s principle of the chevauchement des spécialisations (crossing of specializations), which transformed phylogenetics from a search for ancestor–descendant sequences to research into relative degrees of relationships. This replacement resolved the conflict, much discussed at the time, between the continuity of ancestor–descendant lineages and the discontinuity inherent in the natural (phylogenetic) system. Walter Zimmermann refined Abel’s methodology, which he called character‐phylogenetics (Merkmalsphylogenie), an approach that was eventually adopted by Willi Hennig.     

A combined evidence phylogenetic analysis of Anguimorpha (Reptilia: Squamata)

Anguimorpha is a clade of limbed and limbless squamates with ca. 196 extant species and a known fossil record spanning the past 130 million years. Morphology‐based and molecule‐based phylogenetic analyses disagree on several key points. The analyses differ consistently in the placements of monstersaurs (e.g. Gila Monsters), shinisaurs (Crocodile Lizards), the anguid Anniella (American Legless Lizards), carusioids (Knobby Lizards), and the major clades within Varanus (Monitor Lizards). Given different data sources with such different phylogenetic hypotheses, Anguimorpha is an excellent candidate for a combined phylogenetic analysis. We constructed a data matrix consisting of 175 fossil and extant anguimorphs, and 2281 parsimony‐informative characters (315 morphological characters and 1969 molecular characters). We analysed these data using the computer program TNT using the “new technology search” with the ratchet. Our result is novel and shows similarities with both morphological and molecular trees, but is identical to neither. We find that a global combined evidence analysis (GCA) does not recover a holophyletic Varanoidea, but omission of fossil taxa reveals cryptic molecular support for that group. We describe these results and others from global morphological analysis, extant‐only morphological analysis, molecular data‐only analyses, combined evidence analysis of extant taxa, and GCA. © The Willi Hennig Society 2010.     

Phylogeny of Mysis (Crustacea, Mysida): history of continental invasions inferred from molecular and morphological data

We studied the phylogenetic history of opossum shrimps of the genus Mysis Latreille, 1802 (Crustacea: Mysida) using parsimony analyses of morphological characters, DNA sequence data from mitochondrial (16S, COI and CytB) and nuclear genes (ITS2, 18S), and eight allozyme loci. With these data we aimed to resolve a long‐debated question of the origin of the non‐marine (continental) taxa in the genus, i.e., “glacial relicts” in circumpolar postglacial lakes and “arctic immigrants” in the Caspian Sea. A simultaneous analysis of the data sets gave a single tree supporting monophyly of all continental species, as well as monophyly of the taxa from circumpolar lakes and from the Caspian Sea. A clade of three circumarctic marine species was sister group to the continental taxa, whereas Atlantic species had more distant relationships to the others. Small molecular differentiation among the morphologically diverse endemic species from the Caspian Sea suggested their recent speciation, while the phenotypically more uniform “glacial relict” species from circumpolar lakes (Mysis relicta group) showed deep molecular divergences. For the length‐variable ITS2 region both direct optimization and a priori alignment procedures gave similar topologies, although the former approach provided a better overall resolution. In terms of partitioned Bremer support (PBS), mitochondrial protein coding genes provided the largest contribution (83%) to the total tree resolution. This estimate however, appears to be partly spurious, due to the concerted inheritance of mitochondrial characters and probable cases of introgression or ancestral polymorphism. © The Willi Hennig Society 2005.     

Species: kinds of individuals or individuals of a kind

The “species‐as‐individuals” thesis takes species, or taxa, to be individuals. On grounds of spatiotemporal boundedness, any biological entity at any level of complexity subject to evolutionary processes is an individual. From evolutionary theory flows an ontology that does not countenance universal properties shared by evolving entities. If austere nominalism were applied to evolving entities, however, nature would be reduced to a mere flow of passing events, each one a blob in space–time and hence of passing interest only. Yet if there is genuine biodiversity in nature, if nature is genuinely carved into species, and taxa, then these evolutionary entities will be genuinely differentiated into specific kinds, each species being one of its kind. Given the fact that evolving entities have un‐sharp boundaries, an appropriately weak, “non‐essentialist” concept of natural kind has to be invoked that does not allow for strong identity conditions. The thesis of this paper is that species are not either individuals, or natural kinds. Instead, species are complex wholes (particulars, individuals) that instantiate a specific natural kind. © The Willi Hennig Society 2007.     

石山苣苔属(苦苣苔科)花形态演化及分类学意义

石山苣苔属(苦苣苔科)约30种,主要分布于我国南部的石灰岩地区.目前该属已知物种数虽少但花形态极其多样,是该科中分类最为困难的类群之一.基于分子证据,其它8个属中花形态迥异的一些物种被并入石山苣苔属.然而,该属花形态的演化趋势缺乏系统性的研究,传统分类对属的界定与分子系统学研究结果相矛盾的原因,以及是否有形态特征支持新界定的石山苣苔属还不清楚.该研究中,总共编码了19种石山苣苔属植物和9种报春苣苔属植物的35个形态特征,其中包括26个花部形态特征,在分子系统树上追踪了它们的演化路径.结果表明:无论属内还是属间,多数花部形态特征,尤其以往属的分类界定特征,在演化过程中变化频繁且发生了高度同塑性演化,这是导致传统形态分类不自然的关键因素.此外,在观察研究的所有特征中,花丝和柱头的差异可能在石山苣苔属植物共同祖先中经历了演变,或可用于区分石山苣苔属与其姐妹报春苣苔属的大多数种类.因此,在苦苣苔科植物的分类学研究中应当慎用这些花部性状作为分类依据,而且应对形态特征进行广泛地观察研究,在密集的取样和分辨率更高、更可靠的系统树上追踪它们的演化规律.更为重要的是,需要进一步研究导致复杂形态性状演化的内在分子调控机理和外在的自然选择动力,最终更加深入地理解石山苣苔属等典型喀斯特植物的演化过程和机理.     

Species are individuals—the German tradition

The German tradition of considering species, and higher taxonomic entities, as individuals begins with the temporalization of natural history, thus pre‐dating Darwin’s ‘Origin’ of 1859. In the tradition of German Naturphilosophie as developed by Friedrich Schelling, species came to be seen as parts of a complex whole that encompasses all (living) nature. Species were comprehended as dynamic entities that earn individuality by virtue of their irreversible passage through time. Species individuality was conceived in terms of species taxa forming a spatiotemporally located relational system (complex whole), a conception of species that was easily assimilated to an evolutionary world view. However, the dynamics of an evolutionary process driven by variation and natural selection created a tension between continuity in nature as opposed to the discreteness and relative stasis of species. As a consequence, some authors such as Ernst Haeckel and Karl August Möbius denied the reality of species, while others explicitly linked the reality and individuality of species to their temporal duration. The mature conception of species as individuals, as formulated by Ludwig von Bertalanffy and adopted by Willi Hennig, is one of an historically conditioned, spatiotemporally located, causally integrated, dynamic yet transiently homeostatically stabilized relational system.     

Haeckel's ABC of evolution and development

One of the central, unresolved controversies in biology concerns the distribution of primitive versus advanced characters at different stages of vertebrate development. This controversy has major implications for evolutionary developmental biology and phylogenetics. Ernst Haeckel addressed the issue with his Biogenetic Law, and his embryo drawings functioned as supporting data. We re-examine Haeckel's work and its significance for modern efforts to develop a rigorous comparative framework for developmental studies. Haeckel's comparative embryology was evolutionary but non-quantitative. It was based on developmental sequences, and treated heterochrony as a sequence change. It is not always clear whether he believed in recapitulation of single characters or entire stages. The Biogenetic Law is supported by several recent studies -- if applied to single characters only. Haeckel's important but overlooked alphabetical analogy of evolution and development is an advance on von Baer. Haeckel recognized the evolutionary diversity in early embryonic stages, in line with modern thinking. He did not necessarily advocate the strict form of recapitulation and terminal addition commonly attributed to him. Haeckel's much-criticized embryo drawings are important as phylogenetic hypotheses, teaching aids, and evidence for evolution. While some criticisms of the drawings are legitimate, others are more tendentious. In opposition to Haeckel and his embryo drawings, Wilhelm His made major advances towards developing a quantitative comparative embryology based on morphometrics. Unfortunately His's work in this area is largely forgotten. Despite his obvious flaws, Haeckel can be seen as the father of a sequence-based phylogenetic embryology.     

Scorpion higher phylogeny and classification, taxonomic anarchy, and standards for peer review in online publishing

Soleglad and Fet's (2003a) attempt to reconstruct the phylogeny of Recent (including extant) scorpions, the revised classification derived from it, and recent emendations, mostly published in their self‐edited online journal, Euscorpius, are deficient. Separate analyses of three independent matrices (morphology, 16S rDNA, 18S rDNA) were presented. In the morphological matrix, 52 binary and 10 tristate trichobothrial characters were replaced with one character comprising six ordered states representing trichobothrial “types”. The remaining matrix of 105 characters was further reduced to 33 “fundamental” characters (20% of the morphological dataset), the analysis of which appears to be the basis for the revised classification presented. The taxon sample for the morphological analysis included 14 supraspecific terminal taxa representing genera, the monophyly of only 7 (12.5%) of which has been confirmed. A composite terminal, assembled from the fragments of fossils that may not be confamilial let alone monophyletic, was created for the Palaeopisthacanthidae, employed as the primary outgroup for the analysis. Other important outgroup taxa, notably eurypterids, xiphosurans and other arachnids, were omitted entirely. The morphological characters presented contained numerous unjustifiable assumptions of character polarity and phylogenetic relationship. An approach to character coding, deliberately adopted to reduce “homoplasy”, biased the analysis towards a preconceived result. Structurally and topographically similar features in different taxa were explicitly assigned separate (often autapomorphic) states according to presumed phylogenetic relationships among the taxa in which they were observed. Putative “reversals” were coded as separate characters or states. Character transformation was forced by ordering, additive coding or Sankoff optimization through allegedly intermediate states for which there is no empirical evidence. Many characters were defined in a manner that demonstrates either a lack of understanding of, or disregard for, established methods and standards of morphological character coding. Some states display overlapping variation whereas others subsume variation that is not structurally or topographically similar. Polymorphic “states” were created for terminals with interspecific variation and unknown “states” for terminals that should have been scored unknown. Many characters were not evaluated for particular terminal taxa, but merely scored inapplicable although the structures and, consequently, the characters in question are present and therefore applicable to them. In view of the significant theoretical and empirical problems with the approach to cladistics taken by Soleglad and Fet, we find no justification for accepting either the results of their analyses or the revised classification derived from them. Pending the outcome of a rigorous phylogenetic analysis, published according to acceptable standards of scholarship in a peer‐reviewed journal, we revert to the suprageneric classification of Scorpiones reflected by the most recent peer‐reviewed, published treatments and reject all changes to the classification proposed by Soleglad, Fet and colleagues since 2001. We argue that an analysis and revised classification of the kind presented in various papers by these authors could not survive the peer‐review process of a mainstream scientific journal. The poor scholarship exemplified by these and other papers published in Euscorpius emphasize the importance of quality control associated with the emergent infrastructure of online publishing. A centralized register of taxa may be the only solution for ensuring quality control in the taxonomy of the future. © The Willi Hennig Society 2005.     

Molecular phylogeny and systematics of flowering plants of the family Crassulaceae DC

Crassulaceae (orpine or stonecrop family) is the most species-rich (ca. 1400 spp) family in the order Saxifragales. Most members of the family are succulent plants. Phenotypic diversity and large number of species complicates systematics of the family and obscures reconstruction of relationship within it. Phylogenetic analyzes based on morphological and molecular markers placed Crassulaceae as one of the crown clades of Saxifragales. In this contribution a review of phylogenetic studies on the family Crassulaceae, based on DNA nucleotide sequence comparisons is presented; major clades established in the family are characterised; their structure and polyphylesis of some genera are discussed. It is shown that the traditional taxonomic structure of Crassulaceae contradicts pattern of phylogenetic relationships between its members. We critically analyzed recent taxonomic systems of the family and stress that homoplasy of morphological characters does not allow to use them to reconstruct relationships between crassulacean taxa even at the low taxonomic levels.     

Ernst Haeckel (1834–1919) and the monophyly of life

Ernst Haeckel, who first introduced the term ‘monophyly’ into the biological literature, has in the past been appealed to in adjudication of the modern use of that concept. A contextual analysis of his writings reveals an inconsistent use of the term ‘monophyly’ by Haeckel. Morphological phylogeny was decoupled in Haeckel’s thinking from the evolutionary history of taxa. Monophyly could mean the derivation of one taxon from another, ancestral one, where these taxa could be species or of supraspecific rank. Monophyly could also mean the phylogenetic differentiation of a diversity of organismal ‘forms’ (morphologies) from a common primitive ‘form’ (morphological stage). And finally, monophyly, as also polyphyly, could apply to the origin of specific anatomical structures, in which case the monophyly/polyphyly of anatomical structures needed not to correlate with the monophyly/polyphyly of the taxon characterized by these structures. With respect to the issue of the unity and reality of monophyletic taxa, Haeckel’s writings again are indeterminate as is his stance on the monophyletic origin of life.