Systems theory of evolution
The system theory of evolution goes back in particular to the information - theoretical system theory after Ludwig von Bertalanffy and its application to phenomena of evolution by the Viennese School (including Rupert Riedl ) from the 1970s and represents a further development of the synthetic evolution theory according to Ernst Mayr , which in turn is based on Charles Darwin .
The systems theory of evolution assumes that living organisms are open systems in the sense of thermodynamics , which are in constant equilibrium with their environment . They are characterized by the fact that the states of equilibrium of many factors within living beings differ significantly from the states of equilibrium in the environment. One example is the body temperature of most mammals, which is often well above ambient temperature and, in contrast to it, remains constant. Abiotic systems that are far from equilibrium, such as the Belousov-Zhabotinsky reaction , also show special properties and certain forms of self-organization, for example oscillation .
Critique of the synthetic theory of evolution
The system theory of evolution is particularly dedicated to those phenomena that are not adequately explained by the classical synthetic theory of evolution , for example
- the emergence of profound changes in the basic construction plan ( macroevolution ).
- coevolution, i.e. the parallel evolution of coordinated characteristics in very different species, for example of symbioses
The concept of selection is critically questioned in systems theory.
The systems theory of evolution supplements the concept of external selection in Darwin's definition by that of internal selection. An organism must be coherent in terms of the functionality of its subsystems, otherwise it would not be able to survive (inner fit). If this is not the case, the external, classical selection cannot take effect. For example, a joint developed by nature must function properly according to its design purpose. A mutation in the gene network that codes for the joint can disrupt this adapted functionality and thus be fatal for the organism . Thus the degrees of freedom are also restricted, i.e. the leeway that mutation, recombination, selection create in order to progressively develop organisms and their organs, i.e. H. to be improved with regard to the function that is to be fulfilled in the organism. This means that the change in the external selection conditions can initially only have an indirect effect within the framework of the boundary conditions given by the internal fit. Riedl describes this inner functionality as an evolutionary burden because it resists change. This creates evolutionary constraints that ultimately lead to construction principles known as “construction plans”.
The system theory takes into account that the expression of characteristics is not solely due to the DNA sequence of a gene, but rather a result of a complex interaction of many factors of the entire system of living beings in the course of ontogenesis. Not only genetically determined factors of direct genetic information and control by mechanisms of gene regulation (Riedl: epigenetic system ) and material gradients within an organism, but also external factors such as temperature or the effects of chemical substances during embryonic development have an effect. The set of factors at work in embryogenesis is also known as the epigenetic landscape.
This consideration of the interrelationships should explain why certain developmental stages of ontogenesis should recapitulate stages of phylogeny (see also the outdated theory of basic biogenetic rule ). In terms of system theory, the complexity of ontogenetic development results in development channels. So this limits the amount of possible evolutionary dynamics. The channels of development complement the concept of convergent selection pressures derived from synthetic theory in the explanation of convergences ( e.g. analog organs ). Leaving the development channels enables major changes (macroevolution).
Systems theory also takes into account that the one-gene-one-enzyme hypothesis should not be understood as “one DNA sequence - one characteristic”. There are characteristics that arise from the interaction of many genes (and polypeptides) (polygeny), but also genes that influence several characteristics at the same time ( polyphenia or pleiotropy) (Riedl: The adaptation of a functional unit is therefore not only a favorable but even have to wait for the accumulation of favorable opportunities ). There are also multifactorial characteristics, the expression of which is not only polygenic, but also due to environmental factors. Genes that are responsible for gene regulation play a special role. Thus only the gene regulates Paxx6 in Drosophila melanogaster more than 2000 individual loci . Such master genes can significantly reduce the overall costs of the living being system.
Macro evolution
Macroevolutionary changes can thus be understood through those mutations in regulators and structural genes that cause a whole spectrum of phenotypic changes as a result of changes in gene expression patterns. So these mutations change the entire system. As already can act simple changes profoundly, experiments have mud jumpers , a halbamphibisch in mangrove swamps live fish group shown. After several months of treatment with the thyroxine hormone , a. the following changes: the pectoral fins became bone-like extremities, the skin became thicker, the gills were reduced, and lung breathing increased. In the end, the absence of water was endured significantly longer than without treatment. Sievert Lorenzen on this: In many genotypes lies dormant potencies which, as in the cases mentioned, are only realized through adequate environmental stimuli. On the other hand, even minor genotypic changes can produce quite dramatic effects under certain conditions. These development potentials are also called pre- adaptation, to put it simply, a random adaptation before this proves to be advantageous under selection pressure.
Pre-adaptation
A pre-adaptation can also exist because many features can have a double or multiple function. The evolution of feathers and wings in birds did not necessarily have to take place in a coordinated manner. Feathers were already present in dinosaurs before the development of bird flight and were used for thermal insulation. Recent fossil finds reveal a number of intermediate stages from simple to complex feathers in clearly ground-dwelling dinosaurs. With the evolution of the wing, they could then also be used for flying.
The pre-adaptation has found an additional molecular genetic basis through the discovery of alternative splicing as well as introns and exons . Alternative splicing, in particular, is a prime example of multiple functions and enables the rapid development of new proteins without changing the primary DNA code by recombining already “tried and tested” DNA code sections. If one takes into account that - for example in humans - well over 90 percent of the DNA does not code directly for proteins, it becomes clear what amount of genetic information is available that can in principle be activated for the development of new features by even small changes in the DNA in the area of gene regulation .
See also
literature
- Rupert Riedl: The order of the living. System conditions of evolution Berlin: Parey 1975
Individual evidence
- ^ Rupert Riedl : The Order of the Living 1975; GP Wagner, MD Laubichler (2004): Rupert Riedl and the Re-Synthesis of Evolutionary and Developmental Biology , Journal of Experimental Zoology: Part B, 302B: 92-102
- ↑ Cf. also Günter P. Wagner on the population genetic basis of a systems theory of evolution. In: Jörg Ott , GP Wagner, Franz Wuketits (Hrsg.) Evolution, Order and Knowledge. Berlin: Parey, 1985. pp. 97-111
- ↑ By including synergetics , the system theory of evolution was expanded to a synergetic theory of evolution . See Sievert Lorenzen How to advance from the theory of natural selection towards a General Theory of Self-Organization in Dieter Stefan Peters, Michael Weingarten (eds.) Organisms, genes and evolution: evolutionary theory at the crossroads . Scientific society at the Johann Wolfgang Goethe University in Frankfurt am Main. Writings 2000, Vol. 14, pp. 119-127