The Natural History of Oxygen

The nuclear reactions occurring in the cores of stars which are believed to produce the element oxygen are first described. Evidence for the absence of free oxygen in the early atmosphere of the earth is reviewed. Mechanisms of creation of atmospheric oxygen by photochemical processes are then discussed in detail. Uncertainty regarding the rate of diffusion of water vapor through the cold trap at 70 km altitude in calculating the rate of the photochemical production of oxygen is avoided by using data for the concentration of hydrogen atoms at 90 km obtained from the Meinel OH absorption bands. It is estimated that the present atmospheric oxygen content could have been produced five to ten times during the earth's history. It is shown that the isotopic composition of atmospheric oxygen is not that of photosynthetic oxygen. The fractionation of oxygen isotopes by organic respiration and oxidation occurs in a direction to enhance the O¹⁸ content of the atmosphere and compensates for the O¹⁸ dilution resulting from photosynthetic oxygen. Thus, an oxygen isotope cycle exists in nature.     

The Natural History of Biocatalytic Mechanisms

Phylogenomic analysis of the occurrence and abundance of protein domains in proteomes has recently showed that the α/β architecture is probably the oldest fold design. This holds important implications for the origins of biochemistry. Here we explore structure-function relationships addressing the use of chemical mechanisms by ancestral enzymes. We test the hypothesis that the oldest folds used the most mechanisms. We start by tracing biocatalytic mechanisms operating in metabolic enzymes along a phylogenetic timeline of the first appearance of homologous superfamilies of protein domain structures from CATH. A total of 335 enzyme reactions were retrieved from MACiE and were mapped over fold age. We define a mechanistic step type as one of the 51 mechanistic annotations given in MACiE, and each step of each of the 335 mechanisms was described using one or more of these annotations. We find that the first two folds, the P-loop containing nucleotide triphosphate hydrolase and the NAD(P)-binding Rossmann-like homologous superfamilies, were α/β architectures responsible for introducing 35% (18/51) of the known mechanistic step types. We find that these two oldest structures in the phylogenomic analysis of protein domains introduced many mechanistic step types that were later combinatorially spread in catalytic history. The most common mechanistic step types included fundamental building blocks of enzyme chemistry: “Proton transfer,” “Bimolecular nucleophilic addition,” “Bimolecular nucleophilic substitution,” and “Unimolecular elimination by the conjugate base.” They were associated with the most ancestral fold structure typical of P-loop containing nucleotide triphosphate hydrolases. Over half of the mechanistic step types were introduced in the evolutionary timeline before the appearance of structures specific to diversified organisms, during a period of architectural diversification. The other half unfolded gradually after organismal diversification and during a period that spanned ∼2 billion years of evolutionary history.     

The Specimen Dealer: Entrepreneurial Natural History in America's Gilded Age

The post-Civil War American natural history craze spawned a new institution – the natural history dealer – that has failed to receive the historical attention it deserves. The individuals who created these enterprises simultaneously helped to promote and hoped to profit from the burgeoning interest in both scientific and popular specimen collecting. At a time when other employment and educational prospects in natural history were severely limited, hundreds of dealers across the nation provided encouragement, specimens, publication outlets, training opportunities, and jobs for naturalists of all motivations and levels of expertise. This paper explores the crucial role that specimen dealers played in the larger natural history community. After briefly examining the development of local taxidermy shops in the mid-nineteenth century, it then traces the history of four large natural history dealerships established in the United States during the latter half of the century: Ward's Natural History Establishment, Frank Blake Webster's Naturalists' Supply Depot, Southwick & Jencks' Natural History Store, and Frank H. Lattin & Co. By the early twentieth century, changing tastes in interior design, the growth of the Audubon movement, and the dramatic expansion of alternate training and job opportunities for naturalists led many specimen dealers either to shift their emphasis or to shut their doors. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Ibis: Transformations in a Twentieth Century British Natural History Journal

The contents of the British Ornithologists' Union's journal, The Ibis, during the first half of the 20th century illustrates some of the transformations that have taken place in the naturalist tradition. Although later generations of ornithologists described these changes as logical and progressive, their historical narratives had more to do with legitimizing the infiltration of the priorities of evolutionary theory, ecology, and ethology than analyzing the legacy of the naturalist tradition on its own terms. Despite ornithologists' claim that the journal's increasing focus on "biology" represented a natural development after the preliminary phase of systematics and geographical ornithology, in fact a small group campaigned to bring the priorities of population ecology, behavior, and selection theory into the journal and British ornithology more generally. The problems involved in this transition highlight the importance of methodological and institutional context in determining and reinforcing appropriate research programs for ornithologists. Comparing the discipline-building rhetoric of moderns with the contents of the past illustrates how modern evaluations of 19th century research programs have been enmeshed in ornithologists' endeavors to forge new identities for traditional disciplines.     

Selected Natural Materials in History

1 Technology of natural materials Early man used conveniently shaped stones as tools. ＂Workshop＂ areas have been found with large numbers of stones, some showing signs of being worked. However, organic materials like wood will decay under normal wet conditions in the presence of oxygen, so we won＇t find the same sort of evidence for wooden tools. It is safe to assume that early man used sticks as probes and clubs, and maybe even for making some sort of nestlike protection against the elements and predators, since we see chimpanzees and other animals doing this sort of thing. So wood, and ahnost certainly other plant materials such as fibrous leaves, and bone and other materials gleaned from dead animals, would be used from the earliest times. We need to know this in order to establish the idea that Man can be expected to have a long history of the use and manipulation of natural materials. This needs skills in choosing materials for certain uses on the basis of their mechanical properties, whether those properties are to do with the ease of shaping the material or the effectiveness of that material in use. Occasionally the material was chosen simply because it was readily available. If we find that a particular material was always used for a certain job, it＇s reasonable to deduce that Man was exerting materials selection criteria through experience.     

Before Darwin: Transformist Concepts in European Natural History

Lack of consideration of the complex European scientific scene from the late 18th century to the mid-decades of the 19th century has produced partial and often biased reconstructions of priorities, worries, implicit and explicit philosophical and at times political agendas characterizing the early debates on species. It is the purpose of this paper firstly to critically assess some significant attempts at broadening the historiographic horizon concerning the immediate context to Darwins intellectual enterprise, and to devote the second part to arguing that a multi-faceted European debate on the transformation of life forms had already occurred in Europe around 1800. Of this debate, contrary to long cherished views, Lamarcks was only one voice, amongst many. Naturalists active in different national contexts elaborated solutions and proposed doctrines that shared several viewpoints, yet clearly stemmed from a variety of disciplinary traditions and problematic contexts.     

The Brood Pattern of Mitomycin-C-Induced Translocations in DROSOPHILA MELANOGASTER Males: The Effect of Time

Translocations between the two large autosomes were scored in the progeny of males that had been fed mitomycin-C. The frequencies were the same in spermatogonia sampled after 12 and 25 days and in spermatozoa stored for the same periods in untreated females.     

疾病自然史的随机模型

1前言疾病自然史是指疾病的临床发展过程以及转归〔1〕．有些疾病如早期糖尿病,早期青光眼,肿瘤的临床前状态,往往自觉无症状,一旦自己感觉有症状或临床发现,此时已属于中、晚期,难以取得较好的治疗效果,特别是肿瘤,已经发生了转移．为此,必须早期发现、早期治疗．因此自然史研究有着重要意义．在肿瘤的预防中,它决定着二级预防,筛查方案的优化以及筛查效果的评价．国内外许多文献报道了宫颈癌、乳腺癌、AIDS等自然史的研究成果．在疾病自然史研究中,一般是将疾病分为几个阶段或几个状态,对肿瘤的研究一般是将癌前状态分为几…