lunes, 20 de abril de 2009

Selección del Complexity Digest - Abril

Can evolution explain how minds work?, Nature


Human societies have long used the capability of argumentation and dialogue to overcome and resolve conflicts that may arise within their communities. Today, there is an increasing level of interest in the application of such dialogue games within artificial agent societies. In particular, within the field of multi-agent systems, this theory of argumentation and dialogue games has become instrumental in designing rich interaction protocols and in providing agents with a means to manage and resolve conflicts.

The architecture of mutualistic networks minimizes competition and increases biodiversity, Nature

Excerpt: These networks have been found to be highly nested5, with the more specialist species interacting only with proper subsets of the species that interact with the more generalist. We show that nestedness reduces effective interspecific competition and enhances the number of coexisting species. Furthermore, we show that a nested network will naturally emerge if new species are more likely to enter the community where they have minimal competitive load. Nested networks seem to occur in many biological and social contexts, suggesting that our results are relevant in a wide range of fields.

Final warning from a sceptical prophet, Nature

Excerpt: In The Vanishing Face Of Gaia, Lovelock argues that model projections of the climate a century ahead are of little use. The models of the Intergovernmental Panel on Climate Change (IPCC) extrapolate from a smooth trend of warming, yet the real climate system, complex and fully coupled to the biology of land and ocean, is unlikely to change in this simple way. It is more likely to flip from one state to another, with non-linear tipping points that the IPCC models are too simplistic to capture. Lovelock fears that the climate will shift to a new and considerably hotter regime, and that once underway, this shift will be irreversible.

This title is false, Nature

Excerpt: The [paradoxical] result, like a dog chasing its tail, should be familiar to anyone who has thought about a gene network or biological process. Common descriptions of biological interactions, such as 'This gene represses itself' or 'gene A activates gene B. Gene B inhibits gene A', are similarly self-referential, potentially causing endless cycles.

  • Source: This title is false, Mark Isalan & Matthew Morrison, DOI: 10.1038/458969a, Nature 458, 969, 2009/04/22

Developmental biology: Two by two, Nature

Excerpt: This is not the first time that these villagers have sacrificed their body fluids for science. Mohammad Pur Umri has become somewhat famous, not for the milk or mustard that provides the villagers with their livelihood, but for its prolific production of identical monozygotic twins. Globally, only 1 in every 250 to 300 births are identical twins. In Umri, roughly one in ten is of this type, births that the villagers â€" including the twin village leaders call "gifts from God".

Time to sequence the 'red and the dead', Nature News

Excerpt: "Now it is possible to entertain sequencing the genomes of other extinct and endangered species, and the benefits could be huge." Referring to the 'Red List' of highly endangered species drawn up by the International Union for Conservation of Nature (IUCN), Schuster suggests that researchers should plan for sequencing "the red and the dead: a suite of carefully chosen endangered and extinct species."

The Human Brain Is On The Edge Of Chaos, ScienceDaily

Excerpts: Cambridge-based researchers provide new evidence that the human brain lives "on the edge of chaos", at a critical transition point between randomness and order. The study provides experimental data on an idea previously fraught with theoretical speculation. Self-organized criticality (where systems spontaneously organize themselves to operate at a critical point between order and randomness), can emerge from complex interactions in many different physical systems, including avalanches, forest fires, earthquakes, and heartbeat rhythms. According to this study, (...) the dynamics of human brain networks have something important in common with some superficially very different systems in nature. (...)

Evolution: Biology's next top model?, Nature

Excerpt: As the water temperatures plunged by about 5 °C to below zero over the next few million years, most fish became extinct or moved on to warmer climes. But one group, the Notothenioidei, remained. Thanks to some extraordinary evolutionary innovations, these bottom-dwellers radiated, speciated and ultimately dominated. Crucial proteins shifted shape so they could work at cold temperatures, and a digestive enzyme fragment took on a new role as antifreeze.

On the Origin of Flowering Plants, Science

Excerpt: How did flowering plants diversify and spread so rapidly across the globe? From rice paddies to orange groves, alpine meadows to formal gardens, prairies to oak-hickory forests, the 300,000 species of angiosperms alive today shape most terrestrial landscapes and much of human life and culture. Their blooms color and scent our world; their fruits, roots, and seeds feed us; and their biomass provides clothing, building materials, and fuel. And yet this takeover, which took place about 100 million years ago, apparently happened in a blink of geological time, just a few tens of millions of years.

Mutated Gene In Zebrafish Sheds Light On Blindness In Humans, Innovations-report

Excerpts: Among zebrafish, the eyes have it. Inside them is a mosaic of light-sensitive cells whose structure and functions are nearly identical to those of humans. There, biologists at The Florida State University discovered a gene mutation that determines if the cells develop as rods (the photoreceptors responsible for dim-light vision) or as cones (the photoreceptors needed for color vision). (...) are the first scientists to identify the crucial function of a previously known gene called "tbx2b." The researchers have named the newfound allele (a different form of a gene) "lor" -- for "lots-of-rods" -- because the mutation results in too many rods (...).

Darwin's ‘One Special Difficulty': Celebrating Darwin 200, Biol. Lett.

Abstract: Darwin identified eusocial evolution, especially of complex insect societies, as a particular challenge to his theory of natural selection. A century later, Hamilton provided a framework for selection on inclusive fitness. Hamilton's rule is robust and fertile, having generated multiple subdisciplines over the past 45 years. His suggestion that eusociality can be explained via kin selection, however, remains contentious. I review the continuing debate on the role of kin selection in eusocial evolution and suggest some lines of research that should resolve that debate.

The cancer genome, Nature

Abstract: All cancers arise as a result of changes that have occurred in the DNA sequence of the genomes of cancer cells. Over the past quarter of a century much has been learnt about these mutations and the abnormal genes that operate in human cancers. We are now, however, moving into an era in which it will be possible to obtain the complete DNA sequence of large numbers of cancer genomes. These studies will provide us with a detailed and comprehensive perspective on how individual cancers have developed.

  • Source: The cancer genome, Michael R. Stratton, Peter J. Campbell & P. Andrew Futreal, DOI: 10.1038/nature07943, Nature 458, 719-724, 2009/04/09

Parental Effects In Ecology And Evolution: Mechanisms, Processes And Implications, Phil. Tran. Biol. Sc.

Excerpt: As is the case with any metaphor, parental effects mean different things to different biologists-from developmental induction of novel phenotypic variation to an evolved adaptation, and from epigenetic transference of essential developmental resources to a stage of inheritance and ecological succession. (...) Here, we suggest that by emphasizing the complexity of causes and influences in developmental systems and by making explicit the links between development, natural selection and inheritance, the study of parental effects enables deeper understanding of developmental dynamics of life cycles and provides a unique opportunity to explicitly integrate development and evolution. (...)

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