Bruce Hannon's Complexity Digest #4

Posted by Connie French on Apr 5, 2010 8:55:28 PM

Bruce Hannon is known to many for his weekly email digest highlighting interesting articles, published in various well regarded complexity sources, that span the gamut from all areas of research and inquiry, from the life sciences to the social sciences. What all the articles have in common is that they celebrate interesting findings, provocative theories, and the complexity of the world. Bruce has graciously agreed to allow InnoCentive to repost his “Complexity” Digest from time to time. Thank you Bruce!

Below, you will find Bruce’s “Complexity” Digest #4, we hope you enjoy. Please let us know your feedback and feel free to respond to the blog posts and share your thoughts and reactions with others.

Ageing, Nature

Excerpt: It is now clear that by tinkering with particular signalling pathways and by balancing nutrition, the lifespan of many organisms, including yeast, worms, flies and mice, can be extended. Crucially, the same tweaks often bring about substantial health benefits and seem to delay the onset of age-related diseases. Most of the pathways involved are evolutionarily conserved, so it is likely that some of this research will eventually benefit human health.

  • Source: Ageing, Marie-Thérèse Heemels, DOI: 10.1038/464503a, Nature 464, 503, 2010/03/25

What's Old Is New: 1918 Virus Matches 2009 H1N1 Strain, Science

Excerpt: The "novel" H1N1 swine influenza virus that last year caused the first human pandemic in 4 decades has one feature that is hardly novel: Its surface protein, hemagglutinin (HA) "which spikes cells and starts an infection"closely matches the HA in the H1N1 virus responsible for the 1918 pandemic. Separated by 91 years, the two strains of the highly mutable virus ought to be vastly different. This newfound similarity answers many mysteries about the 2009 pandemic, including why it largely spared the elderly.

Quantifying Emergence in term of Persistent Mutual Information, arXiv

Excerpt: We define Persistent Mutual Information (PMI) as the Mutual (Shannon)Information between the past history of a system and its evolution significantly later in the future. This quantifies how much past observations enable long term prediction, which we propose as the primary signature of (Strong) Emergent Behaviour.

Information dynamics shape the sexual networks of Internet-mediated prostitution, PNAS

Excerpt: Like many other social phenomena, prostitution is increasingly coordinated over the Internet. The online behavior affects the offline activity; the reverse is also true. We investigated the reported sexual contacts between 6,624 anonymous escorts and 10,106 sex buyers extracted from an online community from its beginning and six years on. These sexual encounters were also graded and categorized (in terms of the type of sexual activities performed) by the buyers. From the temporal, bipartite network of posts, we found a full feedback loop in which high grades on previous posts affect the future commercial success of the sex worker, and vice versa.

Spontaneous Synchrony Breaking, arXiv

Abstract: Research on synchronization of coupled oscillators has helped explain how uniform behavior emerges in populations of non-uniform systems. But explaining how uniform populations engage in sustainable non-uniform synchronization may prove to be just as fascinating.

Codd's Self-Replicating Computer, Artificial Life

Excerpt: Edgar Codd's 1968 design for a self-replicating cellular automaton has never been implemented. Partly this is due to its enormous size, but we have also identified four problems with the original specification that would prevent it from working. These problems potentially cast doubt on Codd's central assertion, that the eight-state space he presents supports the existence of machines that can act as universal constructors and computers. However, all these problems were found to be correctable, and we present a complete and functioning implementation after making minor changes to the design and transition table.

Patient Referral Patterns and the Spread of Hospital-Acquired Infections through National Health Care Networks, PLoS Comput Biol
Summary: The prevalence of hospital acquired infections is widely believed to reflect the quality of health care in individual hospitals, and is therefore often used as a benchmark. Intuitively, the idea is that infections spread more easily in hospitals with a poor quality of health care. This assumes that the rate at which admitted patients introduce new infections is the same for all hospitals. In this article, we show that this assumption is unlikely to be correct. Using national data on patient admissions, we are able to reconstruct the entire hospital network consisting of patients referred between hospitals. This network reveals that university hospitals admit more patients that recently stayed in other hospitals. Consequently, they are more likely to admit patients that still carry pathogens acquired during their previous hospital stay. Therefore, the prevalence of infections does not only reflect the quality of health care but also the connectedness to hospitals from which patients are referred. This phenomenon is missed at the single hospital level; our study is the first to address the connectedness between hospitals in explaining the prevalence of hospital acquired infections. Our findings imply that interventions should focus on hospitals that are central in the network of patient referrals.

Evolutionary establishment of moral and double moral standards through spatial interactions, arXiv

Excerpt: Situations where individuals have to contribute to joint efforts or share scarce resources are ubiquitous. Yet, without proper mechanisms to ensure cooperation, the evolutionary pressure to maximize individual success tends to create a tragedy of the commons (such as over-fishing or the destruction of our environment). This contribution addresses a number of related puzzles of human behavior with an evolutionary game theoretical approach as it has been successfully used to explain the behavior of other biological species many times, from bacteria to vertebrates. Our agent-based model distinguishes individuals applying four different behavioral strategies: non-cooperative individuals ("defectors"), cooperative individuals abstaining from punishment efforts (called "cooperators" or "second-order free-riders"), cooperators who punish non-cooperative behavior ("moralists"), and defectors, who punish other defectors despite being non-cooperative themselves ("immoralists"). (...)

Markets, Religion, Community Size, and the Evolution of Fairness and Punishment, Science

Excerpt: Large-scale societies in which strangers regularly engage in mutually beneficial transactions are puzzling. The evolutionary mechanisms associated with kinship and reciprocity, which underpin much of primate sociality, do not readily extend to large unrelated groups. Theory suggests that the evolution of such societies may have required norms and institutions that sustain fairness in ephemeral exchanges. If that is true, then engagement in larger-scale institutions, such as markets and world religions, should be associated with greater fairness, and larger communities should punish unfairness more. Using three behavioral experiments administered across 15 diverse populations, we show that market integration (measured as the percentage of purchased calories) positively covaries with fairness while community size positively covaries with punishment.

The Young, the Weak and the Sick: Evidence of Natural Selection by Predation, PLoS ONE

Excerpt: It is assumed that predators mainly prey on substandard individuals, but even though some studies partially support this idea, evidence with large sample sizes, exhaustive analysis of prey and robust analysis is lacking. [...] This article provides a reliable example of how natural selection may operate in the wild and proves that predators mainly prey on substandard individuals.

The Suppression of Immune System Disorders by Passive Attrition, PLoS ONE

Excerpt: Exposure to infectious diseases has an unexpected benefit of inhibiting autoimmune diseases and allergies. This is one of many fundamental fitness tradeoffs associated with immune system architecture. The immune system attacks pathogens, but also may (inappropriately) attack the host.[...] This study focuses on physiological constraints that lead to competition for survival between immune system cell types.

'Tarzan Economics': If Music Is Free, How Do Artists Get Paid?, Knowledge@Wharton

Summary: Over the past decade, the music industry was roundly criticized for how it responded to the proliferation of digital content -- launching hundreds of lawsuits against otherwise law-abiding consumers who downloaded music. Although many companies have backed off from that approach, the challenge remains to find a business model for digital music. If songs can be downloaded and traded for free, how do the musicians, recording engineers and record company executives get paid?

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