Charles Darwin's theory of evolution: A review of our present understanding

The paper characterizes Darwin's theory, providing a synthesis of recent historical investigations in this area. Darwin's reading of Malthus led him to appreciate the importance of population pressures, and subsequently of natural selection, with the help of the wedge metaphor. But, in itself, natural selection did not furnish an adequate account of the origin of species, for which a principle of divergence was needed. Initially, Darwin attributed this to geographical isolation, but later, following his work on barnacles which underscored the significance of variation, and arising from his work on botanical arithmetic, he supposed that diversity allowed more places to be occupied in a given region. So isolation was not regarded as essential. Large regions with intense competition, and with ample variation spread by blending, would facilitate speciation. The notion of place was different from niche, and it is questioned whether Darwin's views on ecology were as modern as is commonly supposed. Two notions of struggle are found in Darwin's theory; and three notions of variation. Criticisms of his theory led him to emphasize the importance of variation over a range of forms. Hence the theory was populational rather than typological. The theory required a Lamarckian notion of inheritable changes initiated by the environment as a source of variation. Also, Darwin deployed a use/habit theory; and the notion of sexual selection. Selection normally acted at the level of the individual, though kin selection was possible. Group selection was hinted at for man. Darwin's thinking (and also the exposition of his theory) was generally guided by the domestic-organism analogy, which satisfied his methodological requirement of a vera causa principle.     

The Role of Small Islands in Marine Subsistence Strategies: Case Studies from the Caribbean

Caribbean archaeologists have tended to focus exclusively on the prehistory of the largest islands, perhaps because large islands are believed to provide the landmass necessary to support long-term population growth and cultural development. Yet, as research here and elsewhere, e.g., the Pacific, is showing, small islands provided access to resources and landscapes that were not always readily available on the larger islands. Small islands often have superior terrestrial and, especially, marine resources; isolated ritual spaces; and more easily defended locations; although they are susceptible to more rapid overexploitation. This paper examines in detail human needs with regard to island size, demonstrating that small islands were crucial in the development of pre-Columbian Caribbean societies. Four case studies are presented to illustrate that small islands often were preferred over large islands throughout the Caribbean archipelagoes. Finally, these studies show that the prehistoric exploitation and overexploitation of small islands can provide significant insights for establishing baselines that can be used for modern management and conservation efforts.

Darwin's sexual selection: Understanding his ideas in context

Darwin's writings need to be seen in their fullness, as opposed to quote-mining individual sentences without the context of his passages. Sometimes Darwin wrote at length, apparently favorably, about ideas that he subsequently undermined, replacing them with a more integrative view that reflected his own broad compass. Darwin understood that nature is not simple, that not all members of a group may have evolved under the same selective regime, and that variation of all kinds is fundamental to selection in its several forms. Sexual selection requires sexual dimorphism; it is not centred on variation within sexes but on selection for the ability to acquire mates. “Mutual sexual selection” was rejected by Darwin for every species except humans. Mating success is not a matter of mere numbers but of the transmission of the most attractive features to the opposite sex. The term “sexual selection” should only be used when one sex uses a feature not present in the other sex to attract mates or repel rivals for mates.     

Darwin's legacy: the forms,function and sexual diversity of flowers

Charles Darwin studied floral biology for over 40 years and wrote three major books on plant reproduction. These works have provided the conceptual foundation for understanding floral adaptations that promote cross-fertilization and the mechanisms responsible for evolutionary transitions in reproductive systems. Many of Darwin''s insights, gained from careful observations and experiments on diverse angiosperm species, remain remarkably durable today and have stimulated much current research on floral function and the evolution of mating systems. Here I review Darwin''s seminal contributions to reproductive biology and provide an overview of the current status of research on several of the main topics to which he devoted considerable effort, including the consequences to fitness of cross- versus self-fertilization, the evolution and function of stylar polymorphisms, the adaptive significance of heteranthery, the origins of dioecy and related gender polymorphisms, and the transition from animal pollination to wind pollination. Post-Darwinian perspectives on floral function now recognize the importance of pollen dispersal and male outcrossed siring success in shaping floral adaptation. This has helped to link work on pollination biology and mating systems, two subfields of reproductive biology that remained largely isolated during much of the twentieth century despite Darwin''s efforts towards integration.     

Darwin's concept of final cause: neither new nor trivial

Darwin'suse of final cause accords with the Aristotelian idea of finalcauses as explanatory types – as opposed to mechanical causes, which arealways particulars. In Wright's consequence etiology, anadaptation is explained by particular events, namely, its past consequences;hence, that etiology is mechanistic at bottom. This justifies Ghiselin'scharge that such versions of teleology trivialize the subject, But a purelymechanistic explanation of an adaptation allows it to appear coincidental.Patterns of outcome, whether biological or thermodynamic, cannot be explainedbytracing causal chains, even were that possible. They are explicanda of aspecialkind. The form of their explanation, in statistical mechanics or by naturalselection, is not captured by statistical variants of the covering-law model orrelated models of explanation. In them as in classical teleology, types ofoutcome are cited to explain why there are outcomes of those types. But onlywhen types are explanatory by being selected for, as inexplanations of animal and human behavior as well as in Darwin's theory ofnatural selection, but not in statistical mechanics, is the explanationteleological. Darwin's theory is nontrivially teleological.     

On Darwin's palaeontology in The Origin of Species

I investigate the role of palaeontology within Darwin's works through an analysis of the two chapters of The Origin of Species most especially devoted to this science. Palaeontology may occupy several places within the structure of the argumentative logic of Darwinism, but these places have remained to some extent ancillary. Indeed, palaeontology could well document evolutionary patterns, showing the actual occurrence of evolution as a general “historical fact”, but it was poorly adapted to demonstrate the main point of Darwinism: the actual evolutionary process: natural selection acting among individuals. I also show, in agreement with Gould, that Darwin had great confidence in the ultimate ability of palaeontology to support his theory, and that in interpreting palaeontological evidence, he expressed a vision of natural selection much wider and more eclectic than that which has generally been ascribed to him.     

Bacterial Genomic Islands: Organization,Function, and Evolutionary Role

Data on the structural organization and evolutionary role of specific bacterial DNA regions known as genomic islands are reviewed. Emphasis is placed on the most extensively studied genomic islands, pathogenicity islands (PAIs), which are present in the chromosome of Gram-negative and Gram-positive pathogenic bacteria and absent from related nonpathogenic strains. PAIs are long DNA regions that harbor virulence genes and often differ in GC content from the remainder of the bacterial genome. Many PAI occur in the tRNA gene loci, which provide a convenient target for foreign gene insertion. Some PAI are highly homologous to each other and contain sequences similar to ISs, phage att sites, and plasmid ori sites, along with functional or defective integrase and transposase genes, suggesting horizontal transfer of PAI among bacteria.     

Plant-parasitic Nematode Problems in the Pacific Islands

The Pacific islands have a diverse range of food and cash crops with indigenous and introduced nematode problems. The staple food crops have serious nematode pests, such as Meloidogyne spp. on sweet potato, Hirschmanniella miticausa causing corm rot of taro, and Pratylenchus coffeae and Radopholus sp. producing tuber dry rot of yams. Bananas are infested with P. coffeae or R. similis, citrus with Tylenchulus semipenetrans, rice with Aphelenchoides besseyi, and ginger with Meloidogyne spp. and R. similis. Rotylenchulus reniformis, P. zeae, P. brachyurus, and Helicotylenchus spp. are important on all of these and other crops, such as sugarcane, passion fruit, pawpaw, and cassava. Meloidogyne spp. cause serious damage to local and introduced leaf and fruit vegetables and other crops, such as tobacco, sugarcane, pawpaw, black pepper, and pyrethrum. Many other plant-parasitic genera and species, some undescribed, occur in the Pacific, and there are many islands still to be investigated.     

Origin and post-colonization evolution of the Chatham Islands skink (Oligosoma nigriplantare nigriplantare)

Island ecosystems provide an opportunity to examine a range of evolutionary and ecological processes. The Chatham Islands are an isolated archipelago situated approximately 800 km east of New Zealand. Geological evidence indicates that the Chatham Islands re-emerged within the last 1-4 million years, following a prolonged period of marine inundation, and therefore the resident flora and fauna is the result of long-distance overwater dispersal. We examine the origin and post-colonization evolution of the Chatham Islands skink, Oligosoma nigriplantare nigriplantare, the sole reptile species occurring on the archipelago. We sampled O. n. nigriplantare from across nine islands within the Chatham Islands group, and representative samples from across the range of its closest relative, the New Zealand mainland common skink (Oligosoma nigriplantare polychroma). Our mitochondrial sequence data indicate that O. n. nigriplantare diverged from O. n. polychroma 5.86-7.29 million years ago. This pre-dates the emergence date for the Chatham Islands, but indicates that O. n. nigriplantare colonized the Chatham Islands via overwater dispersal on a single occasion. Despite the substantial morphological variability evident in O. n. nigriplantare, only relatively shallow genetic divergences (maximum divergence approximately 2%) were found across the Chatham Islands. Our analyses (haplotypic diversity, Phi(ST), analysis of molecular variance, and nested clade phylogeographical analysis) indicated restricted gene flow in O. n. nigriplantare resulting in strong differentiation between islands. However, the restrictions to gene flow might have only arisen recently as there was also a significant pattern of isolation by distance, possibly from when the Chatham Islands were a single landmass during Pleistocene glacial maxima when sea levels were lower. The level of genetic and morphological divergence between O. n. nigriplantare and O. n. polychroma might warrant their recognition as distinct species.     

High Islands Versus Low Islands: A Comparison of Fish Faunal Composition of the Palau Islands

High islands, with potentially greater habitat diversity, are expected to have greater species richness and diversity compared to low islands, typically atolls and coral islands of lower habitat diversity, within the same geographical area. Patterns of species similarity, richness, and diversity were compared among coral reef fishes between the low island of the Southwest Palau Islands (SWPI), and the low and high islands of the Main Palauan Archipelago (MPA). Data from diurnal visual transects accounted for approximately 64% and 69% of the shorefish faunas known from the SWPI and MPA, respectively. Two distinct fish faunas were representative of low and high islands. The first was confined to the coral islands of the SWPI. The second was partitioned into both low and high islands of the MPA, and Helen Reef, a large atoll in the SWPI. The second type was clustered into atolls, low islands with atoll-like barrier reef systems, a coral island, and three high island systems, one with an extensive barrier reef system. Contrary to the prediction that high islands, with relatively greater habitat diversity, would have greater species richness and diversity, species richness and diversity were greatest at Kossol, a large atoll-like low island locality at the northern end of a high island in the MPA, followed by two atolls, Kayangel (MPA, north of Kossol) and Helen Reef. In contrast, species richness and diversity were lower at high island localities and lowest at small coral islands. These results suggest that habitat diversity for reef fishes increases as a function of increasing area regardless of whether the locality is a high or low island.     

The Postponed Agenda: Archaeology and Human Biogeography in the Twenty-First Century

Scholarly views on the prehistory of the Pacific Islanders are currently undergoing a major shift in perspective and underlying assumptions. This shift is driven by new research data and a need for new theoretical perspectives on space, time, and causal process. A new research agenda is coming to the fore, replacing the agenda guiding Pacific studies since the 1950s. Instead of looking at these islands as remote, undeveloped human colonies scattered across a vast and empty expanse of sea, we are finding that the Pacific was a notably early sphere of human accomplishments, on land and sea, where the ocean was more an avenue than a barrier for cultural interchange. The roots of this new perspective can be traced back, in part, to the Wenner-Gren/Smithsonian conference on human biogeography held in Washington, D.C., in 1974.     

致病岛及其分泌系统

致病岛是指细菌染色体上一段具有典型结构特征的基因簇,主要编码与细菌的毒力及代谢等功能相关的产物。病原菌必须要有一套高效的分泌系统才能将致病因子分泌到细菌表面或转运出细胞,并尽可能进入宿主细胞。现在已经发现了至少5套不同的蛋白分泌系统。本文就致病岛及其分泌系统的相关研究进展作一综述。