From: Science-WeekTo: prismx@scienceweek.com ; prismx@scienceweek.com ; prismx@scienceweek.com ; prismx@scienceweek.com Subject: SW Focus Report - Evolution Date: Tuesday, November 24, 1998 11:59 AM -------------- Enclosure number 1 ---------------- ------------------------------------------------------- SCIENCE-WEEK FREE TRIAL SUBSCRIPTION: This Focus Report is extracted from the full-text Email publication SCIENCE-WEEK. If you have not had a previous free trial subscription to SCIENCE-WEEK, you can subscribe for a 3-issue SW trial without any obligation on your part afterward. To obtain a trial subscription to SCIENCE-WEEK, simply transmit FREE TRIAL to . Full SCIENCE-WEEK subscription details are appended to this file. ------------------------------------------------------- FOCUS REPORT: EVOLUTION A Summary Group from SCIENCE-WEEK ------------------------------------------------- ON EVOLUTIONARY ADAPTABILITY Although developmental and evolutionary biology classically have been distinct research disciplines, one of the consequences of the emergence of molecular biology during the latter half of the 20th century is the apparent active merging of evolutionary and developmental biology at several levels. Kirschner and Gerhart (2 installations, US) present a detailed analysis of the interaction of development and evolution, the analysis amplified in a contiguous paper by West-Eberhard (Smithsonian Tropical Research Institute, US). The essential idea of Kirschner and Gerhart is that flexible development, rather than being an alternative to selection in the evolution of form, mediates the production of selectable variation. They propose that environmentally sensitive developmental flexibility, far from merely interfering with the effects of genes, can ameliorate the deleterious results of mutation and of environmentally induced variation, increasing the viability of novel forms. The authors make the following points: 1) Evolvability (evolutionary adaptability) is an organism's capacity to generate heritable *phenotypic variation. 2) *Metazoan evolution is marked by great morphological and physiological diversification, although the core genetic, cell biological, and developmental processes are largely conserved. 3) Metazoan diversification has entailed the evolution of various *molecular regulatory processes controlling the time, place, and conditions of use of the conserved core processes. 4) These molecular regulatory processes, and certain of the core processes, have special properties relevant to evolutionary change, and these special properties reduce the interdependence of components and confer robustness and flexibility on processes during embryonic development and in adult physiology. 5) These processes also confer evolvability on the organism by reducing constraints on change and allowing the accumulation of nonlethal variation. 6) Evolvability may have been generally selected in the course of selection for robust flexible processes suitable for complex development and physiology, and specifically selected in evolutionary lines undergoing repeated *radiations. The authors present detailed specific examples of various special processes that may be relevant for evolvability, and they conclude: "Today. we see the survivors of lineages that underwent multiple radiations. These lineages have diversified by maintaining a core of highly conserved processes and modifying others. The core processes have unusual capacities to deconstrain change in other processes and components. This has proven to be a powerful strategy for the variation side of Darwin's variation and selection principle of evolution." QY: Marc Kirschner QY: Mary Jane West-Eberhard, Smithsonian Tropical Research Institute, Unit 2511, APO AA 34020-9511 (Proc. Natl. Acad. Sci. US 21 Jul 98 95:8417,8420) (Science-Week 21 Aug 98) ------------------- Related Background: ... ... *phenotypic: The term "phenotype" refers to the total appearance of an organism as determined by the interaction during development between its genetic constitution (genotype) and the environment. Thus, the concept of phenotype has always implied a liaison between developmental and evolutionary biology. The idea of Kirschner and Erhart is that the capacity for phenotypic variation is itself an important evolving evolutionary element. ... ... *Metazoan: In general, the term "metazoa" refers to all multicellular animals. Among important distinguishing characteristics of metazoa are cell differentiation and intercellular communication. For certain multicellular colonial entities such as sponges, some biologists prefer the term "parazoa". ... ... *molecular regulatory processes: An example of a molecular regulatory process discussed by the authors is the regulation of intracellular calcium ion concentration by the calmodulin proteins, this regulation in turn activating or deactivating physiological processes or other regulatory processes. ... ... *radiations: In this context, the term "radiation" refers to the spread of a group of biological entities into new environments with consequent diversification. ON GAIA AND NATURAL SELECTION Considering a global system as complex as the planet Earth and its resident biological entities, there are many possible schemes, some more metaphorical than others, for organizing observations and predicting future events. In recent years, The *Gaia hypothesis first formulated by James E. Lovelock in 1979 has emerged as a possible conceptual framework for studying the interaction of the environment of the surface of the Earth and Earth's biota. The essential aspect of the Gaia hypothesis is the consideration of feedback mechanisms whose consequence is self- regulation of the environment-biota global system with an emphasis on the importance of the biotic component in the physical history of the planet. The Gaia hypothesis has its severe critics, as evidenced in the following view of Tjeerd H. Van Andel (*1994) (University of Cambridge, UK): "The conflict between accepting what science teaches us and what the human heart would like to believe is well illustrated by James Lovelock's Gaia concept that places life in charge of the functioning of our planet. It is a lovely thought, a tempting one too, because it is a form of religion and the human soul requires the comfort of a guided universe; it needs religion. Alas, it is also unnecessary, because the world as it was, has evolved, and now exists, is not explicable. It is merely very complex, and life plays a role in it, but not the main one." This evaluation notwithstanding, the effort to find a workable scheme to generate understanding of environment-biota interactions continues. ... ... Timothy M. Lenton (University of East Anglia, UK) presents an extensive review of the Gaia hypothesis and the place of Darwinian natural selection in that scheme. The author makes the following points: 1) Organisms alter their material environment, and their environment constrains and naturally selects organisms. This connection indicates feedback between life and its environment. 2) The Gaia theory proposes that organisms contribute to self-regulating feedback mechanisms that have kept Earth's surface environment stable and habitable for life, and the theory seeks to explain these mechanisms and how they arise. 3) Natural selection, acting on faithful replication of inherited variation, determines that the organisms that dominate are the ones that leave the most descendants. Together, natural selection and Gaia pose a puzzle: How can self-regulation at the planetary level emerge from natural selection at the individual level? 4) The author attempts to address this puzzle by focusing on the feedbacks to biospheric growth and selective pressures that can arise from environment-altering traits of the biota. Land ecosystems and marine phytoplankton are discussed in terms of several models. The author concludes: "The implications may be far-reaching; simple principles suggest that environmental regulation can emerge at levels from the individual to the global. Natural selection is seen as an integral part of Gaia, and Gaia theory also has something to offer evolutionary biology. Gaian models suggest that we must consider the totality of organisms and their material environment to fully understand which traits come to persist and dominate." QY: Timothy M. Lenton (Nature 30 Jul 98 394:439) (Science-Week 21 Aug 98) ------------------- Related Background: ... ... *Gaia hypothesis: The theory was named for Gaia, the Greek Earth-mother goddess. ... ... *1994: T. H. Van Andel, *New Views on an Old Planet: A History of Global Change*, Cambridge University Press, 1994, p. 402. EVOLUTION: ADAPTIVE RADIATION IN A HETEROGENEOUS ENVIRONMENT The term "adaptive radiation" refers to the rapid evolution of one or a few forms into many different species that occupy different habitats within a new geographical area. The marsupial radiation in Australia illustrates the process: when marsupials were protected from competition with placental mammals by the isolation of the continent, the process led to an entire array of species with widely divergent functions, from herbivores to carnivores. ... ... Rainey and Travisano (University of Oxford, UK) report an investigation of the role of ecological opportunity and competition in driving the genetic diversification associated with adaptive radiation. The form studied was the common aerobic bacterium Pseudomonas fluorescens, which evolves rapidly under novel environmental conditions to generate a large repertoire of mutants. As bacteria reproduce asexually, identical populations can be established from a single genotype, and all subsequent variation is therefore generated de novo by mutation. The authors report that when provided with ecological opportunity, identical populations of P. fluorescens diversify morphologically, but when ecological opportunity is restricted, there is no such divergence. In spatially structured environments, the evolution of variant forms follows a predictable sequence, with competition among the newly evolved niche-specialists apparently maintaining this variation. The authors suggest their results demonstrate that the elementary processes of mutation and selection alone are sufficient to promote rapid proliferation of new designs, and that their results support the theory that trade-offs in competitive ability drive adaptive radiation. QY: Paul B. Rainey (Nature 2 Jul 98 394:69) (Science-Week 31 Jul 98) A MOLECULAR TIMESCALE FOR VERTEBRATE EVOLUTION A timescale is necessary for estimating rates of molecular and morphological change in organisms, and for interpreting patterns of macroevolution and biogeography. Timescales have usually been obtained from the fossil record, where the earliest represent- atives of two lineages establish a minimum time of divergence of these lineages. An alternative method involves the clock-like accumulation of sequence differences in certain genes. Estimates from single genes may have large statistical errors, but studies of multiple genes provide a more reliable estimate of divergence time. ... ... Kumar and Hedges (Pennsylvania State University, US) report an analysis of 658 nuclear genes to provide divergence time estimates for mammalian orders and major lineages of vertebrates. The molecular times agree with most early (Paleozoic) and late (Cenozoic) fossil-based times, but indicate major gaps in the Mesozoic fossil record. The authors propose that at least 5 lineages of placental mammals arose more than 100 million years ago, and most of the modern orders seem to have diversified before the Cretaceous/Tertiary extinction of the dinosaurs. The authors suggest their molecular timescale for vertebrate evolution will be useful in calibrating local molecular clocks and in estimating intra-ordinal divergence times more reliably, especially in groups with poor fossil records. QY: S. Blair Hedges (sbh1@psu.edu) EMAIL (Nature 30 Apr 98 392:917) (Science-Week 22 May 98) DISCOVERY OF OLDEST KNOWN SEA-TURTLE FOSSIL R. Hirayama (Teikyo Heisei University, JP) reports the discovery of an exceptionally well-preserved skeleton of the oldest known chelonioid (sea turtle). Reptiles constitute a primarily terrestrial assemblage, but several groups returned to the marine environment after the first appearance of reptiles in the Paleozoic era. Successful diversification of the chelonioid sea turtles, particularly during the Cretaceous period, was perhaps one of the most important events in the history of turtles (and marine reptiles). The fossil record of chelonioids before the Late Cretaceous has been poorly documented. The skeleton reported by the author is from the Early Cretaceous stage (about 110 mill- ion years before the present) of eastern Brazil. This specimen represents a new taxon, extending the history of chelonioids by 10 million years, and the author suggests it sheds new light on the early evolution of the group: the details of the discovery support the idea that the establishment of the salt-excreting system, and the occupation of a marine habitat, may have preceded the formation of rigid paddles in the history of chelonioids. QY: Ren Hirayama (renhrym@ab.mbn.or.jp) EMAIL (Nature 16 Apr 98 392:705) (Science-Week 8 May 98) ON CONFRONTING CREATIONIST FALLACIES If there is any arena in which the interface between the scientific community and society at large is of importance it is the education of the public, and especially the education of the young public. And perhaps no part of that arena in the US is of more consequence to many citizens than the attempt by certain groups to fashion the teaching of science according to preconceived religious views. ... ... D. Wise (Franklin and Marshall College, US) reviews the current controversy between the scientific community and creationists and discusses a strategy of intellectual confrontation. Among other things, Wise enumerates the following creationist ideas from the Bible that are totally irreconcilable with extant scientific data: 1) the Earth came into existence before the sun and stars; 2) the land plants came into existence before the Sun; 3) the first life forms were plants; 4) fruit trees appeared before fish; 5) fish appeared before terrestrial arthropods; 6) birds appeared before land reptiles. Indeed, the acceptance of any of these ideas with a restraint of consistency results in the tearing down of the entire fabric of modern science (and the tearing down of all its applications, including modern medicine). Wise concludes, "As scientists, we must emphasize repeatedly that the argument against creationism is not against religion as such but rather against a fringe group's attempt to force the Bible into the public schools in the guise of a science textbook... The time has come to stop fighting defensive skirmishes and start challenging creationists to defend in toto what they call science -- humorous absurdities and all." QY: Donald U. Wise (American Scientist Mar/Apr 1998) DISCOVERY OF 3-DIMENSIONAL ALGAE AND ANIMAL EMBRYO FOSSILS A phosphorite is a sedimentary rock composed chiefly of phosphate minerals. The Proterozoic era (also called the Algonkian) is the geologic time between the Archean and the Paleozoic, with the Archean beginning about 3.9 billion years ago and involving the first appearance of sedimentary rocks and the first primitive organisms at the bottom of the oceans. In paleontology, the term "radiation" refers to a diverging and diversifying spread of animals or plants into new environments with a resultant production of new evolutionary forms, and the Ediacaran radiation refers to an assemblage (until now the oldest) of soft-bodied marine animals, the assemblage first discovered in the Ediacara Hills in Australia. The algae comprise a large mixed group of photosynthetic and essentially single-celled plants, and are considered ancestral to modern green plants. Thalli are primitive types of plant bodies not differentiated into stems, leaves, and roots; the term also refers to the gametophyte generation (the phase of the plant life cycle producing reproductive cells) of some ferns and lichens. The term "cleavage stages" refers to the early stages of embryo formation when the egg cell rapidly divides into smaller and smaller cells. The "Bilateria" are a major division of the animal kingdom comprising all forms with bilateral symmetry, and the term "bilaterians" refers to the first such forms appearing after the emergence of protozoa. The term "phylogeny" refers to the evolutionary history of an organism or group of organisms. ... ... Xiao et al (3 authors at 2 installations, US CN) report the discovery of phosphorites of the late Neoproterozoic (570 +- 20 million years ago) in the Doushantuo Formation, southern China, an apparent exceptional record of multicellular life from just before the Ediacaran radiation of macroscopic animals. Abundant thalli with cellular structures preserved in 3-dimensional detail show that late- Proterozoic algae already possessed many of the anatomical and reproductive features seen in modern marine flora. Embryos preserved in early cleavage stages indicate the divergence of lineages leading to bilaterians may have occurred well before their macroscopic traces or body fossils appear in the geological record. The authors suggest that discovery of these fossils shows that the early evolution of multicellular organisms is amenable to direct paleontological inquiry, and that paleontological observations, together with insights from molecular phylogeny and developmental genetics, can facilitate a modern integration of phylogeny, development, and paleontology that extends deeply into evolutionary history to address the early evolution of multicellular life. QY: Andrew H. Knoll, Botanical Museum, Harvard University, 617-495-1000 (Nature 5 Feb 98) PRECAMBRIAN SPONGES WITH CELLULAR STRUCTURES The sponges (Porifera) are a phylum of primitive multi-cellular animals (Metazoa), always attached at one point to a substrate, usually without a definite symmetry, and usually marine. The sponge body is a loose aggregation of cells with little intercellular coordination, but the cells are specialized into various types with various functions important to the viability of the entire organism. There is also in sponges an internal "skeleton" of chalk, silica, or protein, and "calcareous sponges" are sponges containing a relatively large amount of calcium carbonate. In this report, "spicules" are the hard internal structures in sponges composed primarily of silica or calcium salts, and a "monoaxonal" spicule is a spicule having essentially only one dimension (e.g., needle-like). The term "epidermis" refers to the outermost layer of cells in any multicellular organism; "porocytes" are tubular cells that constitute the walls of certain sponges; "amoebocytes" are freely moving cells (sponge cells in this context) within a metazoan tissue; "sclerocytes" are cells involved in the formation of the sponge skeleton; "spongocoel" refers to the branching internal cavity of a sponge, the cavity having a connection in one place or another to the external aqueous environment; "flagella" are long and thin cellular organelles that protrude from the surfaces of cells and are specialized to produce locomotion. The Cambrian period extended from 545 to 505 million years ago, and was the time during which many multicellular organisms first arose, and the Vendian period is the Precambrian metazoan fossil period. The term "Cambrian explosion" refers to the apparent relatively sudden appearance of an enormous number of living forms during the Cambrian period. ... ... Li et al (3 authors at 2 install- ations, TW CN) report the identification of sponge remains in the Early Vendian Doushantuo phosphate deposit (cf. report #8, this issue) in south China. The skeletons consist of siliceous monoaxonal spicules, with preserved soft tissues including the epidermis, porocytes, amoebocytes, sclerocytes, and spongocoel, and among thousands of metazoan embryos a sponge larva having a shoe-shaped morphology and dense peripheral flagella. The authors suggest the data indicate the calcareous sponges may have an extended history in the Late Precambrian, and that animals lived 40 to 50 million years before the Cambrian explosion. They further suggest these Doushantuo rocks provide a potentially inexhaustible resource for understanding the early evolution of animal life. QY: Chia-Wei Li, National Tsing Hua Univ., Hsinchu, Taiwan, China (Science 6 Feb 98) A MODEL FOR THE EVOLUTION OF THE GENETIC CODE Eukaryotic cells are cells with discrete organelles such as nuclei, mitochondria, etc. As organelles, the mitochondria, which are of prime importance in the oxygen metabolism of eukaryotes, are a special class, since it is generally believed they probably originated as primitive cells that established themselves in symbiotic arrangements in the interiors of larger cells. The mitochondria, in fact, carry their own DNA and thus their own genetics. In mathematics, a Lie algebra (named after M.S. Lie 1842-1899) is a system of vector fields on a topological space in which independent quantities are reduced to groupings whose relationships are then subject to algebraic operations. In the context of this report, the term "representation theory" refers to the study of algebraic groups by the use of their represent- ations, with the representation of a group given by a virtual "mapping" of the group onto a group of another type. Pyrimidine and purine are precursors of DNA nucleotide bases. A codon is the elemental genetic coding unit, a triplet of 3 consecutive nucleotides that define a specific amino acid. Some amino acids are determined by more than one codon, leading to a degeneracy (redundancy) in the genetic code. ... ... Bashford et al (3 authors at University of Tasmania, AU) present a model for the structure and evolution of the eukaryotic and vertebrate mitochondrial genetic codes based on the representation theory of a Lie superalgebra, with a key role played by pyrimidine and purine exchange symmetries in codon quartets. The authors suggest that the group theoretical technique is able to give a succinct account of many of the currently understood aspects of the evolution of the genetic code and the observed degeneracy structure of the codon:amino-acid correspondences, and that their particular model is susceptible to quantitative verification. QY: P.D. Jarvis (Proc. Natl. Acad. Sci. US 3 Feb 98) DISCOVERY OF OLDEST KNOWN ANT FOSSILS The ants are one of the most successful extant species, until now believed to have first appeared about 40 million years ago. With the wasps, bees, and termites, they are remarkable as invertebr- ates exhibiting colonies that involve division of labor and a complex social organization. The so-called "Turonian" geologic stage (92 million years ago) corresponds approximately to the Upper or Middle Cretaceous period. ... ... Agosti et al (3 authors at American Museum of Natural History New York, US) now report fossil ants, including a new genus of Ponerinae, approximately 50 million years older than the previous oldest specimens. The discoveries were made in New Jersey (US) in amber from the Turonian stage, and include 3 worker and 4 male ants. The authors suggest the specimens have important implications for dating the origin of ants, and extend the age of an extant ant subfamily back about 50 million years. QY: Donat Agosti (Nature 29 Jan 98) LAND-MASS MIGRATIONS OF LATE CRETACEOUS MAMMALS We have already noted the Cretaceous period as the geological period ranging approximately from 146 million years ago to 65 million years ago. During this period the geographical distrib- ution of Earth's land masses was apparently substantially differ- ent than it is today. Some 375 million years ago, two large supercontinent called Laurasia and Gondwana comprised most or all of the present continental land masses, Laurasia in the north and Gondwana in the south. These two supercontinents merged into the single supercontinent Pangaea about 250 million years ago, and subsequent fragmentation of Pangaea began about 180 million years ago and the fragmentation eventually produced the continental land masses we know today. During this fragmentation there existed the second phase of Gondwana, incorporating what is now South America, Africa, Antarctica, Australia, and India. This historical picture, which is the present general consensus, is the result of a large number of geological and paleobiological studies, and in paleobiology one important task is to reconstruct the land mass migrations of the fauna and flora evolving through- out these large-scale geographical alterations. Now Krause et al (5 authors at 4 installations, US IN DE) report the occurrence of a highly specialized and distinctive group of extinct mammals, the Sudamericidae (Gondwanatheria), in the late Cretaceous of Madagascar and India. The authors suggest these new fossil records are the first evidence of gondwanatheres outside South America, and the first indication of cosmopolitanism among late Cretaceous Gondwanan mammals. They also suggest that Antarctica may have served as an important Cretaceous biogeographic link between South America and Indo-Madagascar. QY: David W. Krause (Nature 4 Dec 97) -------------------- Copyright (c) 1997,1998 Science-Week/Spectrum Press All Rights Reserved for information: http://scienceweek.com request@scienceweek.com -------------------- SCIENCE-WEEK Subscriptions: ----------------------------------------------- Please note: Educational and other nonprofit institutions and organizations are eligible for group subscription rates for SCIENCE-WEEK: 50+ subscribers at a subscription rate of US$1 per year per subscriber, with SW delivered individually to each Email address. For more complete information about group subscriptions, please query at: ----------------------------------------------- SCIENCE-WEEK INDIVIDUAL SUBSCRIPTION INFORMATION: ------------------------------------------------- Subscriptions run for 52 issues at a cost of US$10.00 for the year, and begin with the next issue following receipt of payment. 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