Search Results

This chapter elaborates on a theory of the co-evolution of social networks—a synthesis of social science and biochemistry—and shows its empirical significance for the study of human organizations. First, the chapter describes the problem of organizational novelty in the context of multiple social networks. Second, the core dynamic motor of autocatalysis both at the level of chemical and economic production and at the level of the biographical production of persons through interactive learning, communication, and teaching is explained. Third, the chapter describes eight network mechanisms of organizational genesis that have been discovered in this volume's case studies. Finally, it points to the important outstanding issue of structural vulnerability to tipping.

This chapter provides an extensive review of the biochemistry literature on the origins of life where the concept of autocatalysis figures most prominently. There is a lively debate in the scientific literature between scientists who subscribe to an RNA-first hypothesis and scientists who subscribe to a metabolism-first hypothesis about the origin of life. Both are different versions of autocatalysis, and a sensible conclusion could be that biological life really took off when a symbiosis developed between the two. After that, the chapter reviews past formal modeling in this area, which is spotty but highly suggestive. The chapter identifies Eigen's and Schuster's model of hypercycles as the path-breaking work that first placed empirical chemistry and formal models into fruitful dialogue with each other. Finally, the chapter reviews a less successful, more philosophical descendant of autocatalysis called autopoiesis, which is the guise under which autocatalysis first was presented to social scientists.

Random tessellations and cellular structures occur in many domains of application, such as astrophysics, ecology, telecommunications, biochemistry and naturally cellular biology (see Stoyan, Kendall and Mecke 1987 or Okabe, Boots, Sugihara and Chiu 2000 for complete surveys). The theoretical study of these objects was initiated in the second half of the twentieth century by D. G. Kendall, J. L. Meijering, E. N. Gilbert and R. E. Miles, notably. Two isotropic and stationary models have emerged as the most basic and useful: the Poisson hyperplane tessellation and the Poisson–Voronoi tessellation. Since then, a large majority of questions raised about random tessellations have concerned statistics of the population of cells (‘how many cells are triangles in the plane?’, ‘how many cells have a volume greater than one?’) or properties of a specific cell (typically the one containing the origin). Two types of results are presented below: exact distributional calculations and asymptotic estimations. In the first part, we describe the two basic constructions of random tessellations (i.e. by throwing random hyperplanes or by constructing Voronoi cells around random nuclei) and we introduce the fundamental notion of typical cell of a stationary tessellation. The second part is devoted to the presentation of exact distributional results on basic geometrical characteristics (number of hyperfaces, typical k‐face, etc.). The following part concerns asymptotic properties of the cells. It concentrates in particular on the well‐known D. G. Kendall conjecture which states that large planar cells in a Poisson line tessellation are close to the circular shape. In the last part, we present some recent models of iterated tessellations which appear naturally in applied fields (study of crack structures, telecommunications). Intentionally, this chapter does not contain an exhaustive presentation of all the models of random tessellations existing in the literature (in particular, dynamical constructions such as Johnson‐Mehl tessellations will be omitted). The aim of the text below is to provide a selective view of recent selected methods and results on a few specific models.

The extraordinary development of physical science over the last two centuries has led to claims that it can explain all aspects of reality. Some scientists have proposed a programme called (scientific) reductionism, describing how this is to be achieved. This chapter argues that the world is too complex and inter-related for an explanation of everything to be possible. (‘possible’ means possible in fact, not possible in principle). Application of the reductionist method to biochemistry and cell physiology, money, information and complexity, and subjective consciousness are discussed.

This chapter describes the kinds of learning and memory which are relevant for clinical practice and how they are defined and delineated. Two main lines are followed: one which divides information processing with respect to time, and another with respect to contents. It addresses questions concerning how information is transmitted in the brain (encoded, stored, or represented), and how information is retrieved. It describes the anatomical circuits and networks engaged in these processes with references made to the brain's biochemistry (transmitters, hormones), as far as it is relevant for learning and memory, and such disorders.

This chapter takes up three important areas in which continuing progress in molecular biology relied heavily on frankly biochemical orientation. It argues that the often understated contributions of biochemistry to molecular biology were actually substantial and in many cases indispensable to rapid progress. Many historians point only to the discovery of DNA as they extend their accounts from a brief mention of biochemical genetics. The nature and replication of phage could not have been appreciated without early biochemical characterizations. And the Central Dogma would have remained a poorly examined dogma indeed had it not gained the flesh that orthodox biochemists put on it between 1955 and 1965.

Life on Earth began several billion years ago. The cerebral cortex of mammals probably arose from the primordial cortex of amphibians and reptiles some 300 million years ago. The evolution of the mammalian brain has involved the disproportionate enlargement of the cortex and, in particular, the rapid development of the neocortex. This book explains what is known about the fundamental mechanisms that underlie the development of the neocortex of mammals, drawing on supporting evidence from other species, particularly other vertebrates. The developmental biology of cortical cells and the morphology of the structures that they form is interwoven with a detailed account of their biochemistry and the genetic origin of the factors that are thought to control key developmental processes. While the primary account of the development of the neocortex necessarily is of the results of experimental neuroscience, where appropriate the results are interpreted on the basis of the various formal models that have been proposed. Understanding the mechanisms of cortical development will have a great impact on our ability to comprehend and treat neurological diseases.

To create the nervous system, precise synaptic connections must form between cells. This process involves the outgrowth of axons, their travel to distant sites, and their innervation of target structures. Axons travel together in discrete bundles, which in the adult can be several centimetres long. However, at the time of axonal outgrowth the distances to be travelled are very much shorter than this. There is a range of possible types of mechanism which can yield guidance with differing degrees of precision. This chapter examines the mechanisms for axon guidance, cortical connections in the adult brain, observations on the development of cortical connections, geniculocortical development, corticofugal and corticocortical systems, mechanisms controlling the development of axonal connections, the biochemistry of growth cones, genetic analysis of axonal guidance in non-mammalian species, and mechanisms of axonal guidance in the cerebral cortex.

This chapter examines how ancient DNA (aDNA) analysis has helped reconstruct ancient history. It focuses in particular on cases investigating Roman history. History leaves traces in the human genome as well as those of pathogens and domesticates. While much can be gleaned from the genetic fossils preserved in extant genomes, genomes are palimpsests, with more recent events overwriting previous ones in part. The study of aDNA—DNA preserved in archaeological, paleontological, and museum sources—permits investigations into the genome before and after historic events and observations into how it evolves in real time. The field of aDNA also has a palimpsestic nature in which older results are not only extended and revised, but totally discarded due to rapid technological advances. The chapter briefly describes biochemistry of ancient DNA and the history of its research. Through several key case studies, it shows the potential for aDNA research to clarify the course of ancient history, and also highlights some of its weaknesses and limitations.

This chapter discusses some aspects of the biochemistry of migraine predisposition, and indicate how some of the initiating factors may interact with the central monoamine systems. Professor Lance and others have discussed persuasively how these centres (particularly the raphe nuclei and locus coeruleus) may be involved in the generation of a migraine attack. It is likely that the more we understand about individual vulnerability, the more we may be able to tailor specific treatment to particular patients.

Scientists have access to artifacts of evolutionary history, but they have limited ability to infer the exact events that produced today’s living world. An intriguing question to arise from this limitation is whether the evolutionary paths of organisms are dominated by controlled processes, or whether they are inherently random, subject to different outcomes if repeated. Two experimental approaches, ancestral sequence reconstruction and experimental evolution, can be used to recapitulate ancient adaptive pathways and provide insights into the mutational steps that constitute an organism’s genetic heritage. Ancestral sequence reconstruction follows a backwards-from-present-day strategy in which ancestral forms of a gene or protein are reconstructed and studied mechanistically. Experimental evolution, by contrast, follows a forward-from-present-day strategy in which microbial populations are evolved in the laboratory under defined conditions. Here I describe a novel hybrid of these two methods, in which synthetic components constructed from inferred ancestral gene or protein sequences are placed into the genomes of modern organisms that are then experimentally evolved. Through this system, we aim to establish the comparative study of ancient phenotypes as a novel, statistically rigorous methodology with which to explore the impacts of biophysics and chance in evolution within the scope of the Extended Synthesis.

In 1999, deCODE Genetics printed a “code of ethics” written by “a group of deCODE employees,” with the Ethics Institute of the University of Iceland listed as “Advisors.” No people were listed, just these collectivities. The twenty-page booklet with a heavy blue-paper cover was produced and mailed to the entire population of Iceland. As is often the case with ethics, and particularly codes of ethical principles, there is not a single concrete noun in deCODE's principles that signifies any specific historical, cultural, or institutional body or event; there is only a homogeneous population of bland abstractions. Biochemistry has more to do with ethics, in Halldór Laxness's view, than any theological or even humanist exegesis. “There is only one world in existence,” was the chord struck by the organist, “and in it there prevail either expedient or inexpedient conditions for those who are alive.” This elevation of “expediency” to a kind of ethical principle intrigued the author, and it kept reoccurring in Laxness's novel The Atom Station, often in tandem with biochemical references.

This chapter follows radioisotopes into the laboratories of biochemists and molecular biologists, where they illuminated metabolic pathways and genetic transmission. Early isotope labelling experiments involved stable isotopes, but with the availability of radioisotopes from the AEC, biochemists began relying more on radioactive labels. The chapter features two case studies: Melvin Calvin and Andrew Benson’s elucidation of the steps of photosynthesis using carbon-14, and the role of sulfur-35 and phosphorus-32 in the 1953 Hershey-Chase experiment and other gene transfer experiments (including the so-called “suicide experiments” with phage). Both of these experiments helped establish radiolabeling as a central technique among biochemists and molecular biologists.

This chapter focuses on Robert Sinsheimer's intention to remind his colleagues that their “hard-won recognition of the role of DNA” had brought them only to the beginning of a “new era in genetics and biochemistry.” It begins with a special lecture entitled “First Steps Toward a Genetic Chemistry” that Sinsheimer delivered at the dedication of the Church Laboratory in November 1956. Sinsheimer spoke as a member of the network surrounding Delbruck but one who stood somewhat apart from the enthusiasms of the phage group. Meselson and Stahl were present for the Church Laboratory celebrations and may have heard Sinsheimer's lecture, but his comments about the replication of DNA apparently did not lead to any discussions with them about their plans to test the various proposals for “accomplishing this feat.”