Alfred Gierer

• Aggregates of previously isolated cells of Hydra are capable, under suitable solvant conditions, of regeneration forming complete animals. In a first stage, ecto- and endodermal cells sort out, producing the bilayered hollow structure characteristic of Hydra tissue; thereafter, heads are formed (even if the original cell preparation contained no head cells), eventually leading to the separation of normal animals with head, body column and foot. Hydra appears to be the highest type of organism that allows for regeneration of the entire structure from random cell aggregates. The system is particularly useful for studying cell interactions, tissue polarity, pattern formation, and cell differentiation.

Biological evolution and technological innovation, while differing in many respects, also share common features. In particular, implementation of a new technology in the market is analogous to the spreading of a new genetic trait in a population. Technological innovation may occur either through the accumulation of quantitative changes, as in the development of the ocean clipper, or it may be initiated by a new combination of features or subsystems, as in the case of steamships. Other examples of the latter type are electric networks that combine the generation, distribution, and use of electricity, and containerized transportation that combines standardized containers, logistics, and ships. Biological evolution proceeds, phenotypically, in many small steps, but at the genetic level novel features may arise not only through the accumulation of many small, common mutational changes, but also when distinct, relatively rare genetic changes are followed by many further mutations. In particular, capabilities of biologically modern man may have been initiated, perhaps some 150 000 years ago, by one or few accidental but distinct combinations of modules and subroutines of gene regulation which are involved in the generation of the neural network in the cerebral cortex. It is even conceivable that it was one primary genetic event that initiated the evolution of biologically modern man, introducing some novel but subtle feature of connectivity into the cerebral cortex which allowed for meta-levels of abstraction and upgraded modes of information processing. This may have set the stage for the evolution of integrated but diverse higher capabilities such as structured language, symbolic thought, strategic thought, and cognition based empathy.

Validity of physical laws for any aspect of brain activity and strict correlation of mental to physical states of the brain do not imply, with logical necessity, that a complete algorithmic theory of the mind-body relation is possible. A limit of decodability may be imposed by the finite number of possible analytical operations which is rooted in the finiteness of the world. It is considered as a fundamental intrinsic limitation of the scientific approach comparable to quantum indeterminacy and the theorems of logical undecidability. An analysis of these limits, applied to dispositions of future behaviour, suggests that limits of decodability of the psycho-physic relation may actually exist with respect to brain states with self-referential aspects, as they are involved in mental processes. Limits for an algorithmic theory of the mind-body problem suggested by this study are formally similar to other intrinsic limits of the scientific method such as quantum indeterminacy and mathematical undecidability which are also related to self-referential operations. At the metatheoretical level, hard sciences, despite their reliability, universality and objectivity, depend on metatheoretical presuppositions which allow for multiple philosophical interpretations. -/- .

The essay is an English version of the German article "Wissenschaftliche Rationalität, menschliches Bewusstsein und pro-religiöse Ideen". It discusses immanent versus transcendent concepts in the context of the art of living, as well as the understanding of human consciousness in the context of religion. Science provides us with a far reaching understanding of natural processes, including biological evolution, but also with deep insights into its own intrinsic limitations. This is consistent with more than one interpretation on the “metatheoretical“, that is on the philosophical and cultural level, including liberal, enlightened forms of religion as well as agnostic views. Choices and preferences are mainly a matter of wisdom and art of living, and not just of knowledge, and this, in my view, supports metaphysical and anthropological optimism as expressed in liberal pro-religious ideas. Within Christian theology, metaphysical optimism and openness are most characteristic for the ideas of “apokatastasis” – “salvation for all” - repeatedly condemned as heretical, but also widely supported from early Christianity to modern times.

The development of modern science has depended strongly on specific features of the cultures involved; however, its results are widely and trans-culturally accepted and applied. The science and technology of electricity provides a particularly interesting example. It 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 trans-cultural 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 centuries. Quantum physics and relativity are particularly impressive examples.

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, which is also available online on this server. -/- -/- .

The full text of this essay is available in an English translation (also in philpapers) under: Alfred Gierer, Science, religion, and basic biological issues that are open to interpretation. Der Artikel bildet das Schlusskapitel des Buches " Alfred Gierer: Wissenschaftliches Denken, das Rätsel Bewusstsein und pro-religiöse Ideen", Königshausen&Neumann, Würzburg 2019. Reichweite und Grenzen naturwissenschaftlicher Erklärungen ergeben sich zum einen aus der universellen Gültigkeit physikalischer Gesetze, zum anderen aus prinzipiellen, intrinsischen Grenzen der Bestimmbarkeit und Berechenbarkeit, zumal bei selbstbezüglichen Fragestellungen. In diesem Essay geht es um deutungsoffene Grundfragen in Zusammenhang mit der Beziehung von Wissenschaft und Religion: Der Unterscheidung von Tier und Mensch, der Entstehung der mentalen Fähigkeiten der biologischen Spezies „Mensch“, den naturgesetzlichen Voraussetzungen eines „lebensfreundlichen“ physikalischen Universums, und der Reichweite wie den Grenzen einer naturwissenschaftlichen Erklärung von menschlichem Bewusstsein. Naturwissenschaft kann auf der philosophischen, kulturellen und religiösen Ebene die Mehrdeutigkeit der Welt nicht auflösen. Agnostische und religiöse Grundauffassungen werden auf Dauer ko-existieren, und die Wahl ist nicht nur eine Frage des Wissens, sondern besonders auch der Weisheit und der Lebenskunst.

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 paper addresses the formation of striking patterns within originally near-homogenous tissue, the process prototypical for embryology, and represented in particularly purist form by cut sections of hydra regenerating, by internal reorganisation of the pre-existing tissue, a complete animal with head and foot. The essential requirements are autocatalytic, self-enhancing activation, combined with inhibitory or depletion effects of wider range – “lateral inhibition”. Not only de-novo-pattern formation, but also well known, striking features of developmental regulation such as induction, inhibition, and proportion regulation can be explained on this basis. The theory provides a mathematical recipe for the construction of molecular models with criteria for the necessary non-linear interactions. It has since been widely applied to different developmental processes.

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.

What, precisely, are the ‘changing perspectives on reality’ in contemporary scientific thought? The topics of the lecture are the scope and the limits of science with emphasis on the physical foundations of biology. The laws of physics in general and the physics of molecules in particular form the basis for explaining the mechanism of reproduction, the generation of structure and form in the course of the development of the individual organism, the evolution of the diversity and complexity of organisms by mutation and selection, and the control of behaviour by information processing in the nervous system. However, the application of scientific thought to its own foundations reveals some basic limitations in science: indeterminacy in quantum physics, the limits of decidability in mathematics, and, most likely, the limitations of an algorithmic theory of the brain-mind relationship. In all these cases, the application of scientific methods to their own presuppositions leads us to recognize their intrinsic limitations. These limits, in turn, are closely related to fundamental philosophical questions on the relationship between human knowledge and reality. Modern science is consistent with different, though of course not all, interpretations of man and the universe, including the religious interpretations of the universe as God’s creation and man as God’s (mentally creative) image.

Applying mild methods of preparation, part of the ribosomes of rabbit reticulocytes are found in aggregates (later called polyribosomes) of up to six ribosomal units. Upon treatment with RNA-ase, they desintegrate into single ribosomes. The fast-sedimenting aggregates are found to be more active in protein synthesis in terms of incorporation of radioactive amino acids, whereas the single ribosomes are more receptive to stimulation by the artificial messenger RNA poly-U. The findings indicate that the linkage of ribosomes into aggregates is due to the messenger RNA. They support a tape-reading mechanism of protein synthesis whereby growth of the peptide chain is accompanied by shifting the active site of the ribosome from one coding group of nucleotides of the messenger RNA to the next.

Georg Ernst Stahl (1659-1734) was a German physician and chemist. The book (in German) documents a symposium of the Academy Leopoldina on his works and thoughts that contributed to the Enlightenment. Der weite Horizont seines Denkens und seiner Arbeiten umfasst die Phlogiston-Theorie der Verbrennung, die später mit der Entdeckung des Sauerstoffs widerlegt wurde, aber dennoch wichtige Erkenntnisse zur Reversibilität von Reaktionen und zur unsichtbaren Persistenz der beteiligten chemischen Komponenten beitrug. Seine Gedanken zur Rolle der „Anima“, die heute überholt erscheinen, führten bereits am Beginn des 18. Jahrhunderts Konzepte ein, die für die moderne Biologie und Psychologie von Bedeutung sind. Dazu zählen etwa Homöostase, Synergie, die Vorbereitung willentlicher Bewegungen und Unterschiede zwischen unbewussten aber vernünftigen Handlungen und solchen, die von rationalen Erwägungen geleitet werden. Stahls medizinisches Hauptwerk ist die „Theoria medica vera”, Halle 1708. Eine der zentralen Publikationen zur chemischen Theorie der Verbrennung ist die „Zymotechnia fundamentalis seu fermentationis theoria generalis”, Halle 1697, in deutscher Sprache 1734. Siehe auch „Georg Ernst Stahl (1659-1734), German Physician and Chemist“, Artikel von A. Gierer, in: Encyclopedia of the Enlightenment (Hg. A.C. Kors), Bd. 4, Oxford University Press, New York 2003, S. 124-125.

Socioeconomic inequalities are functions not only of intrinsic differences between persons or groups, but also of the dynamics of their interactions. Inequalities can arise and become stabilized if there are advantages (such as generalized wealth including “human capital”) which are self-enhancing, whereas depletion of limiting resources is widely distributed. A recent theory of biological pattern formation has been generalized, adapted and applied to deal with this process. Applications include models for the non-Gaussian distribution of personal income and wealth, for overall economic growth in relation to inequalities and for effects of uncoupling strategies between developing and developed countries. Note added after publication: The equations (14) for the model of the income distribution, with its characteristic non-Gaussian extension towards higher incomes (fig.4), are closely related to the Fokker-Planck equation that is widely applied in many fields of physics.

An English translation of the essay and an extended introduction are included in the download. In diesem Essay geht es um ein religionsfreundliches Selbst- und Weltverständnis, das die Reichweite der menschlichen Vernunft ebenso wie deren intrinsische Grenzen achtet. In dem weiten Feld wählen wir hier Betrachtungen des mittelalterlichen Philosophen und Theologen Meister Eckhart aus. Eckhart (ca.1260-1338) gilt vielen als Mystiker, anderen als Philosophen des Christentums. Er war wohl Beides. Philosophisch ist seine Lehre, die einzelne menschliche Seele habe einen göttlichen, unvergänglichen Urgrund; eher mystisch die These, dieser Urgrund bedarf einer „Gottesgeburt“ in der Seele, ein Loslassen von allen Bestrebungen, einschließlich dem Bestreben, sich gottgefällig zu verhalten. Mir geht es hier nur um den philosophischen Aspekt mit Betonung auf Erkenntnis.

Nikolaus von Kues ist eine der faszinierendsten Persönlichkeiten im Übergang vom Mittelalter zur Neuzeit. Während seine theologischen und neuplatonischen Vorstellungen viel beachtet werden, gilt das weniger für seine naturphilosophischen Ideen: Wie Gott die Welt in Wirklichkeit, so schafft der Mensch sie in Gedanken. Beobachtung, Experiment und Mathematik sind zum Verständnis der Natur notwendig. Die biblische Überlieferung ist nicht wörtlich zu nehmen. Er propagierte ein fast unendliches Universum ohne Mittelpunkt und Begrenzung mit einer sich bewegenden Erde. Besonders bedeutsam im Hinblick auf Reichweite und Grenzen moderner Naturwissenschaft ist seine Theorie des "Wissens vom Nichtwissen": Wissenschaft selbst ist geeignet, ihre eigenen Grenzen zu erkennen. Die Schrift würdigt auch die Persönlichkeit des Cusanus und schließt mit einem Essay über die Beziehung von Naturwissenschaft und Religion in unserer Zeit. The booklet is a re-edition of sections on Nicolas de Cusa in my book "Die gedachte Natur" (1991), also in philpapers. Cusanus was of one of the most original philosophers of the early Renaissance. He gave reasons for human self-confidence: as God created the world order in reality, man creates it in his mind. Not only mathematics, but also quantitative experiments, are essential for understanding nature. Human rationality is superior to verbal interpretations of the Bible: the universe is almost infinite, with no limits and no centre, and with a moving earth. And he insisted on what he considered to be the highest form of knowledge: the knowledge of the limits of knowledge, with far-reaching implications for the philosophy of nature and human cognition.