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Upon separation of the protein from the nucleic acid component of tobacco mosaic virus by phenol, using a fast and gentle procedure, the nucleic acid is infective in assays on tobacco leaves. A series of qualitative and quantitative control experiments demonstrates that the biological activity cannot depend on residual proteins in the preparation, but is a property of isolated nucleic acid which is thus the genetic material of the virus.
Within the sedimentation diagram of infective RNA preparations isolated from Tobacco Mosaic Virus, undegraded molecules form a sharp peak with a molecular weight corresponding to the total RNA content of the virus particle. Degradation kinetics by ribonuclease is of the linear, single-target type, indicating that the RNA is single-stranded. The intact RNA of a virus particle thus forms one big single-stranded molecule. Quantitative evaluation of the effect degradation by RNA-ase on the infectivity of the RNA shows that the integrity of the entire molecule is required for its biological activity.
The generation of viral mutants in vitro was demonstrated by treatment of the isolated RNA of Tobacco Mosaic Virus by nitrous acid. This agent causes deaminations converting cytosine into uracil, and adenine into hypoxanthine. Our assay for mutagenesis was the production of local lesions on a tobacco variety on which the untreated strain produces systemic infections only. A variety of different mutants are generated in this way. Quantitative analysis of the kinetics of mutagenesis leads to the conclusion that alteration of a single out of the 6000 nucleotides of the viral RNA is sufficient for causing a mutation.
Ancient Greek philosophers were the first to postulate the possibility of explaining nature in theoretical terms and to initiate attempts at this. With the rise of monotheistic religions of revelation claiming supremacy over human reason and envisaging a new world to come, studies of the natural order of the transient world were widely considered undesirable. Later, in the Middle Ages, the desire for human understanding of nature in terms of reason was revived. This article is concerned with the fundamental reversal of attitudes, from “undesirable” to “desirable”, that eventually led into the foundations of modern science. One of the earliest, most ingenious and most interesting personalities involved was Eriugena, a theologian at the Court of Charles the Bald in the 9th century. Though understanding what we call nature is only one of the several aspects of his theological work, his line of thought implies a turn into a pro-scientific direction: the natural order is to be understood in abstract terms of ‘primordial causes’; understanding nature is considered to be the will of God; man encompasses the whole of creation in a physical as well as a mental sense. Basically similar ideas on the reconciliation of scientific rationality and monotheistic religions of revelation were conceived, independently and nearly simultaneously, by the Arab philosopher al-Kindi in Bagdad. Eriugena was more outspoken in his claim that reason is superior to authority. This claim is implicit in the thought of Nicholas of Cusa with his emphasis on human mental creativity as the image of God’s creativity; and it is the keynote of Galileo’s ‘Letter to the Grand Duchess Christina’ some 800 years later, the manifesto expressing basic attitudes of modern science. This article in English is based on the monography (in German): A. Gierer “Eriugena, al-Kindi, Nikolaus von Kues - Protagonisten einer wissenschaftsfreundlichen Wende im philosophischen und theologischen Denken”, Acta Historica Leopoldina 29 (1999), Barth Verlag in MVH Verlage Heidelberg, ISBN: 3-335-00652-6
The development of modern science has depended strongly on specific features of the cultures involved; however, its results are widely and transculturally accepted and applied. The science and technology of electricity, for example, emerged as a specific product of post-Renaissance Europe, rooted in the Greek philosophical tradition that encourages explanations of nature in theoretical terms. It did not evolve in China presumably because such encouragement was missing. The transcultural acceptance of modern science and technology is postulated to be due, in part, to the common biological dispositions underlying human cognition, with generalizable capabilities of abstract, symbolic and strategic thought. These faculties of the human mind are main prerequisites for dynamic cultural development and differentiation. They appear to have evolved up to a stage of hunters and gatherers perhaps some 100 000 years ago. However, the extent of the correspondence between some constructions of the human mind and the order of nature, as revealed by science, is a late insight of the last two centuries. Unless we subscribe to extreme forms of constructivism or historical relativism, we may take the success and the formal structure of science as indications of a close, intrinsic relation between the physical and the mental, between the order of nature and the structure of human cognition. At the metatheoretical level, however, modern science is consistent with philosophical and cultural diversity.
Understanding cooperative human behaviour depends on insights into the biological basis of human altruism, as well as into socio-cultural development. In terms of evolutionary theory, kinship and reciprocity are well established as underlying cooperativeness. Reasons will be given suggesting an additional source, the capability of a cognition-based empathy that may have evolved as a by-product of strategic thought. An assessment of the range, the intrinsic limitations, and the conditions for activation of human cooperativeness would profit from a systems approach combining biological and socio-cultural aspects. However, this is not yet the prevailing attitude among contemporary social and biological scientists who often hold prejudiced views of each other's notions. It is therefore worth noticing that the desirable integration of aspects has already been attempted, in remarkable and encouraging ways, in the history of thought on human nature. I will exemplify this with the ideas of the fourteenth century Arab-Muslim historian Ibn Khaldun. He set out to explicate human cooperativeness - "asabiyah" - as having a biological basis in common descent, but being extendable far beyond within social systems, though in a relatively unstable and attenuated fashion. He combined psychological and material factors in a dynamical theory of the rise and decline of political rulership, and related general social phenomena to basic features of human behaviour influenced by kinship, expectation of reciprocity, and empathic emotions.
Die Anwendung der Naturgesetze auf das verhaltenslenkende Gehirn widerspricht auf den ersten Blick der Freiheit des menschlichen Willens. Entsprechendes gilt für die Anwendung der Allmacht Gottes auf alle Vorgänge einschliesslich des menschlichen Verhaltens. Bei einem zweiten Blick auf diese scheinbar so konsequenten Gedankengänge erkennt man aber Verstrickungen in Selbstbezüglichkeiten, die jeweils Mehrdeutigkeiten und Grenzen unseres möglichen Wissens implizieren. Diese zeigten sich schon in Gödels Grenzen mathematisch-logischer Entscheidbarkeit ebenso wie in Heisenbergs Unbestimmtheitsgesetzen der Quantenphysik. Entsprechende Grenzen könnte es für eine vollständige physikalisch begründete Theorie unseres Bewußtseins und damit auch des menschlichen Willens geben - schliesslich würde sie Bewußtsein von Bewußtsein implizieren. In der theologischen Gedankenlinie wiederum kann sich die Allmacht Gottes auch auf die Allmacht selbst richten, indem sie eine weise naturgesetzliche Ordnung ohne ständige göttliche Eingriffe begr ündet und darin den Menschen als Freien will - so etwa sahen es freiheitsfreundliche unter den Theologen wie Eriugena und Cusanus. Mein Essay weist darauf hin, dass selbst bei so verschiedenen Denkweisen wie den naturwissenschaftlichen und theologischen jeweils analoge Selbstbezüglichkeiten auftreten, die unsere Erkenntnis begrenzen.
The introductory personal remarks refer to my motivations for choosing research projects, and for moving from physics to molecular biology and then to development, with Hydra as a model system. Historically, Trembley’s discovery of Hydra regeneration in 1744 was the begin¬ning of developmental biology as we understand it, with passionate debates about preformation versus de novo generation, mechanisms versus organisms. In fact, seemingly conflicting bottom-up and top-down concepts are both required in combination to understand development. In modern terms, this means analysing the molecules involved, as well as searching for physical principles underlying development within systems of molecules, cells and tissues. During the last decade, molecular biology has provided surprising and impressive evidence that the same types of mol¬ecules and molecular systems are involved in pattern formation in a wide range of organisms, including coelenterates like Hydra, and thus appear to have been “invented” early in evolution. Likewise, the features of certain systems, especially those of developmental regulation, are found in many different organisms. This includes the generation of spatial structures by the interplay of self-enhancing activation and “lateral” inhibitory effects of wider range, which is a main topic of my essay. Hydra regeneration is a particularly clear model for the formation of defined patterns within initially near-uniform tissues. In conclusion, this essay emphasizes the analysis of development in terms of physical laws, including the application of mathematics, and insists that Hydra was, and will continue to be, a rewarding model for understanding general features of embryogenesis and regeneration.
Die moderne Naturwissenschaft hat auch ihre prinzipiellen, intrinsischen Grenzen zum Thema gemacht; auf der „metatheoretischen“, nämlich der philosophischen und kulturellen Ebene erweist sie sich als offen für unterschiedliche, wissenschaftlich und logisch konsistente Deutungen - sowohl religiöse als auch agnostische. Die Wahl ist nicht nur eine Frage des Wissens, sondern der Weisheit und der Lebenskunst, und die wiederum spricht für anthropologischen und metaphysischen Optimismus. In diesem Essay geht es dabei um ein religionsfreundliches Selbst- und Weltverständnis, das die Reichweite der menschlichen Vernunft ebenso wie deren intrinsische Grenzen achtet. Es ergänzt und erweitert die Thematik der Schrift „Wissenschaft, Religion und die deutungsoffenen Grundfragen der Biologie“ (2009), (http://www.mpiwg-berlin.mpg.de/Preprints/P388.PDF). Es konzentriert sich nicht nur auf Biologie, es berührt auch den Vergleich immanenter und transzendenter Auffassungen im Allgemeinen und verweist auf einige zentrale theologische Aspekte, was die gegenwärtige Situation und das Verständnis des Christentums angeht. Es steht in Zusammenhang mit Schriften des Autors, die im BBAW edoc Server online verfügbar sind und in denen auch Literaturhinweise zur Thematik zu finden sind. Dazu gehören eine Monographie über Eriugena, al-Kindi, Nikolaus von Kues; Artikel zur Arbeitsgruppe „Humanprojekt“ der BBAW über „Bewusstsein – Reichweite und Grenzen naturwissenschaftlicher Erklärung“ und zum Band „Was ist der Mensch?“; sowie Beiträge zur Arbeitsgruppe „Gemeinsinn und Gemeinwohl“ und zum Thema der „Debatte 1“ der BBAW „Freiheit des menschlichen Willens“.
Die moderne Naturwissenschaft hat auch ihre prinzipiellen, intrinsischen Grenzen zum Thema gemacht; auf der „metatheoretischen“, nämlich der philosophischen und kulturellen Ebene erweist sie sich als offen für verschiedene, wissenschaftlich und logisch konsistente Deutungen – sowohl religiöse als auch agnostische. Die Wahl ist nicht nur eine Frage des Wissens, sondern der Weisheit und der Lebenskunst, und die wiederum spricht für anthropologischen und metaphysischen Optimismus. Diese Zusammenfassung des letzten der hier wiedergegeben Texte kann auch über der ganzen Reihe stehen. Die Arbeiten entstanden von 1985 bis 2014, und sie betreffen und betonen recht verschiedene Aspekte, wenn sich auch eine gewisse Redundanz nicht vermeiden lässt. Es geht um ein religionsfreundliches Selbst- und Weltverständnis, das die Reichweite der menschlichen Vernunft ebenso wie deren intrinsische Grenzen achtet.