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Post-genomics, Evo-Devo and the recurrence of teleologic thought†

Paul Gottlob Layer
Paul Gottlob Layer
   | 25 maj 2022
BioCosmos: New perspectives on the origin and evolution of life's Cover Image
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Article Category: Review
Data publikacji: 25 maj 2022
Zakres stron: 12 - 25
DOI: https://doi.org/10.2478/biocosmos-2022-0002
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© 2022 Paul Gottlob Layer, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Figure 1

Two concepts of gene action in comparison. – a. The classic concept of one gene-one protein was strictly deterministic. The environment (including the inner milieu of the developing embryo) remains irrelevant (white background). A particular gene, and its coded protein were assigned only one function. – b. According to a postgenomic conception, one gene can code for more than one protein, and be involved in many functions. Note feedback effects on gene switches (ON/OFF; blue arrow), which are derived from many environmental sources (dotted blue background; misses in a.).
Two concepts of gene action in comparison. – a. The classic concept of one gene-one protein was strictly deterministic. The environment (including the inner milieu of the developing embryo) remains irrelevant (white background). A particular gene, and its coded protein were assigned only one function. – b. According to a postgenomic conception, one gene can code for more than one protein, and be involved in many functions. Note feedback effects on gene switches (ON/OFF; blue arrow), which are derived from many environmental sources (dotted blue background; misses in a.).

Figure 2

Avian Formenkreise as analyzed by Otto Kleinschmidt (denoted as “super-species” by E. Mayr), exemplified here with the long-tailed tit (Aegithalos caudatus): regional variations are arranged vertically from Sweden (on top) to the Pyrenees (bottom), while variations within local populations are presented side by side (30,31).
Avian Formenkreise as analyzed by Otto Kleinschmidt (denoted as “super-species” by E. Mayr), exemplified here with the long-tailed tit (Aegithalos caudatus): regional variations are arranged vertically from Sweden (on top) to the Pyrenees (bottom), while variations within local populations are presented side by side (30,31).

Figure 3

Evo-Devo can (in theory) explain a macroevolutionary transition from a saurian to a serpent’s bauplan by only two mutational steps of master genes (scheme, simplified): in step 1 expression of a Hox-gene is extended toward the front (anteriorily, left), suppressing formation of front legs, thereby achieving an evolutionary status of limb reduction as revealed in ancient snakes (e.g., pythons, boas; their skeleton still presents remnants of pelvis girdle and hind limbs). In step 2, a 2nd master gene inhibits formation of hind limbs, a status found in young snakes (e.g., vipers).
Evo-Devo can (in theory) explain a macroevolutionary transition from a saurian to a serpent’s bauplan by only two mutational steps of master genes (scheme, simplified): in step 1 expression of a Hox-gene is extended toward the front (anteriorily, left), suppressing formation of front legs, thereby achieving an evolutionary status of limb reduction as revealed in ancient snakes (e.g., pythons, boas; their skeleton still presents remnants of pelvis girdle and hind limbs). In step 2, a 2nd master gene inhibits formation of hind limbs, a status found in young snakes (e.g., vipers).

Figure 4

Modular phenotypic change in a bird with additional pair of legs at its hind end documents “Evo-Devo in action”. Supposedly, only minor genetic changes have caused these drastic malformations, e.g., induced by hormonal stress (c.f. also Fig. 3). Note normal morphology of additional legs (see text: drive to wholeness – holism, teleonomy). Evidently, such a malformation will not provide any survival advantage, and thus will not evolutionarily persist. Yet this specimen exemplifies the occurrence of abrupt and far-reaching alterations (specimen and photo: laboratory of author).
Modular phenotypic change in a bird with additional pair of legs at its hind end documents “Evo-Devo in action”. Supposedly, only minor genetic changes have caused these drastic malformations, e.g., induced by hormonal stress (c.f. also Fig. 3). Note normal morphology of additional legs (see text: drive to wholeness – holism, teleonomy). Evidently, such a malformation will not provide any survival advantage, and thus will not evolutionarily persist. Yet this specimen exemplifies the occurrence of abrupt and far-reaching alterations (specimen and photo: laboratory of author).

Figure 5

H. P. Wilson and H. Driesch – two widely forgotten fathers of regeneration and stem cell biology. Driesch was the eminent proponent of Neovitalism.
H. P. Wilson and H. Driesch – two widely forgotten fathers of regeneration and stem cell biology. Driesch was the eminent proponent of Neovitalism.

Figure 6

Target-directed self-organization in reaggregated spheroids from chick embryonic retina, initiated by cells of outer retina. A. experimental set-up (left, 6 days-old embryo; right, reaggregated spheroid); b. section of “rosetted spheroid” (cf., right in a), presenting PR rosettes(ros), and IPL-like synaptic areas (ipl); c. higher magnification of a rosette (ros) and a close-by ipl; d. so-called stratospheroid with correct and complete laminar organization, onl is outside and gcl is inside (d. on right, chicken retina for comparison); e. enlarged ipl presenting formation of synaptic subbands. Stainings: DAPI (blue) for cell nuclei; b. Pax6 (red) for Acs; c. visinin (green) for PRs; vimentin (yellow) for MCs; d. CERN901 (red) for PRs, dACs (green); e. calretinin (green) for Acs; ChAT (red) for SACs. Note different magnifications in a-e. Abbreviations: INL, ONL, inner and outer nuclear layer; GCL, ganglion cell layer; IPL, OPL, inner and outer plexiform layer; PR, photoreceptor; HC, horizontal cell; BP, bipolar cell; AC, amacrine cell; dAC, displaced amacrine cell; SAC, starburst amacrine cell; GC, ganglion cell; ChAT, choline acetyltransferase; ros, cell rosette holding mitotic cells and/or photoreceptors. Figs. 6a, b, d from (1); Figs. 6 c, e from (64).
Target-directed self-organization in reaggregated spheroids from chick embryonic retina, initiated by cells of outer retina. A. experimental set-up (left, 6 days-old embryo; right, reaggregated spheroid); b. section of “rosetted spheroid” (cf., right in a), presenting PR rosettes(ros), and IPL-like synaptic areas (ipl); c. higher magnification of a rosette (ros) and a close-by ipl; d. so-called stratospheroid with correct and complete laminar organization, onl is outside and gcl is inside (d. on right, chicken retina for comparison); e. enlarged ipl presenting formation of synaptic subbands. Stainings: DAPI (blue) for cell nuclei; b. Pax6 (red) for Acs; c. visinin (green) for PRs; vimentin (yellow) for MCs; d. CERN901 (red) for PRs, dACs (green); e. calretinin (green) for Acs; ChAT (red) for SACs. Note different magnifications in a-e. Abbreviations: INL, ONL, inner and outer nuclear layer; GCL, ganglion cell layer; IPL, OPL, inner and outer plexiform layer; PR, photoreceptor; HC, horizontal cell; BP, bipolar cell; AC, amacrine cell; dAC, displaced amacrine cell; SAC, starburst amacrine cell; GC, ganglion cell; ChAT, choline acetyltransferase; ros, cell rosette holding mitotic cells and/or photoreceptors. Figs. 6a, b, d from (1); Figs. 6 c, e from (64).

Figure 7

Alternate routes of target-directed self-organization in reaggregated spheroids from a mammalian neonatal retina (Gerbil, Mongolian desert rat), initiated by cells of inner retina. A-c) ipl formation is leading target (not PR rosettes, as in Fig. 1): in control reaggregates, calretinin+ ACs (red) sort out and begin to organize an ipl, including synaptic subbands (at 7, 9, 12 dic., resp.); d) inside- out laminar retina: in presence of RPE, all ACs and dACs plus their ipl become arranged under surface (outside) of spheroid; HCs and few PRs are found inside); e) shows in vivo gerbil retinaat P9 for comparison; f) correct laminar structure and advanced ipl differentiation: addition of Wnt-3b and RPE counteracts laminar inversion (as seen in d), and promotes ipl differentiation. Stainings: calretinin+ (red) for Acs and dACs; CERN901 (green) for PRs. For abbreviations., see legend to Fig. 6. Figs. 7a-d from (65); Fig. 7e, f from (66).
Alternate routes of target-directed self-organization in reaggregated spheroids from a mammalian neonatal retina (Gerbil, Mongolian desert rat), initiated by cells of inner retina. A-c) ipl formation is leading target (not PR rosettes, as in Fig. 1): in control reaggregates, calretinin+ ACs (red) sort out and begin to organize an ipl, including synaptic subbands (at 7, 9, 12 dic., resp.); d) inside- out laminar retina: in presence of RPE, all ACs and dACs plus their ipl become arranged under surface (outside) of spheroid; HCs and few PRs are found inside); e) shows in vivo gerbil retinaat P9 for comparison; f) correct laminar structure and advanced ipl differentiation: addition of Wnt-3b and RPE counteracts laminar inversion (as seen in d), and promotes ipl differentiation. Stainings: calretinin+ (red) for Acs and dACs; CERN901 (green) for PRs. For abbreviations., see legend to Fig. 6. Figs. 7a-d from (65); Fig. 7e, f from (66).

Process & terms Explanation
Assimilation, genetic Environment-dependent phenotypic alterations, which are inherited and fixed in progeny.
EcoEvo-Devo Ecological Evo-Devo processes, directed by environmental conditions.
Environment as used in here, does not only refer to external surrounds of an organism, but internal environments, from molecular to cellular to organismic, etc.
Epistemic closure of SET Mindset of SET proponents to neglect opposing arguments (see 20).
Constraints Development-dependent restrictions on evolution, i.e., physical, or morphogenetic constraints; c.f., tinkering.
Epigenetic patterns Individually acquired molecular changes on DNA or histone levels; epigenetic patterns can be passed on; contradicts Weismann’s barrier.
Gene duplication Important for evolution: entire families of related genes originated via gene duplication (i.e., Hox genes). One of the two duplicated genes first can be redundant to only later take on a certain new function.
Genocentrism Gene-centric determinism of NeoD, postulating that the genotype exclusively determines the phenotype.
Gradualism Concept that evolutionary change occurs at a slow and steady rate; opposite to punctualism.
Holism Here: tendency to establish whole structures (teleonomy; cf. Fig. 4).
Hox genes Important family of developmental genes (master genes). On gene level they present a conserved homeobox (sequence of 180 nucleotides), on protein level a homeodomain of 60 amino acids.
Genotype Genetic outfit of an individual.
Canalization Conditional regulation of development; e.g., by environment; c.f., constraints.
Convergence, evolutionary Independent evolution of similar features in non-related organisms, to adapt to similar environment.
Macroevolution Large and abrupt morphologic changes of species in evolution.
Microevolution Minor evolutionary alterations; c.f., Macroevolution.
Modularity Not only morphology is modular, but also many DNA regions, which can function as enhancers.
Mosaic theory of animal development August Weismann’s postulate, according to which the later cell fate (the cell type) is fixed right after fertilization in so-called cleavage cells. In most cases, this presumption is false.
Nature-vs.-Nurture Discussion Question of relative influences of the genome versus environment on development and life of organisms.
Neodarwinism Standard theory of evolution (SET), as developed in the 1st half of 20th century.
Neolamarckism Epigenetics shows that environmentally-acquired individual traits can - under certain circumstances - be passed on into the next generation.
Organoids Spherical (3D) cell constructs cultured from stem cells, which resemble histotypic tissue or organ structures; cf., cell spheroids.
Parsimony, molecular „Molecular toolbox“: Development works with (is achieved by) a restricted set of genetic and molecular networks.
Phenotype Morphologic appearance of an organism; the organism „as a whole“.
Plasticity, phenotypic Environment-dependent morphologic adaptation, i.e., jaw size dependent on diet; becomes genetically fixed.
Pleiotropy Capacity of a gene to code for various functions in different cells.
Ploidy, degree of Number of sets of chromosomes in a cell, e.g., haploid, diploid, polyploid = single, double and more than double set of chromosomes.
Punctualism Opposite of gradualism, see above.
Regulation, biologic Regeneration of a whole bodily structure from few (stem) cells, i.e., regeneration of lizard tail.
Robustness Property of developmental processes to reliably (re-)establish a certain target structure; cf. teleonomy.
Teleology Directionality of biologic processes, incl. metaphysical “vital” forces; distinction to teleonomy; see next.
Teleonomy Directionality of biologic processes, driven by natural forces; opposite to teleology.
The Big Five 5 major periods of mass extinctions at approx. 440, 365, 250, 210 and 65 mys ago.
Tinkering, with „toolbox“ Spatio-temporal expression of identical or similar genes (or their resp. proteins) can lead to alternate phenotypes, through mechanism of:

Heterotopy (gene expression at different locations of embryo),

Heterochrony (g.e. at different times),

Heterometry (g.e. defines size or shape of a structure),

Heterotypy (g.e. alters respective protein structure).
Vitalism, biologic Meaning here: Life conceived as unique unseizable phenomenon, influenced by some transcendental vital force; cf. teleology.
Weismann barrier Weismann’s obsolete postulate of segregation of early germ and somatic cells; e.g., that genetic information is passed on exclusively via the germline, without any influence from environment; c.f., epigenetic patterns, Neolamarckism.
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