30 research outputs found
Evolutionary Dilemmas in a Social Network
We simulate the prisoner's dilemma and hawk-dove games on a real social
acquaintance network. Using a discrete analogue of replicator dynamics, we show
that surprisingly high levels of cooperation can be achieved, contrary to what
happens in unstructured mixing populations. Moreover, we empirically show that
cooperation in this network is stable with respect to invasion by defectors.Comment: 13 pages, 9 figures; to be published in Lecture Notes in Computer
Science 200
Outcomes and long-term follow-up of 106 cats treated with subcutaneous ureteral bypass for ureteral obstruction
Subcutaneous ureteral bypass (SUB) is the main therapy for cats with benign
ureteral obstructions (UO). However, variables associated with outcome and disease
progression remain to be characterized. In this retrospective study, medical records
of all cats treated with SUB (Vetsuisse Faculty of Bern, 2014-2020) were reviewed
(n=106 cats). Short-term outcome was defined as hospital discharge; long-term
outcome as the rate of progression of serum creatinine >120 days after surgery.
Hospital discharge rate was 86%. During follow-up, 22% of the cats required revision
surgeries and 27% had ≥1 positive urine culture. Median survival time was 1.9 years
(95% confidence interval, 1.4-3.2), with 50% urinary-related causes of death. Of the
clinical variables available at presentation, only younger age was associated with
better short-term outcome (P=.008). A lower creatinine at discharge was associated
with favorable long-term outcome (P=.02). The median increase in serum creatinine
during follow-up was 0.14 mg/dL/year (interquartile range, -0.05 to 0.83); 75% of the
cats were classified as stable. Positive urine cultures at the time of diagnosis or
treatment with hemodialysis before surgery for severe azotemia were not associated
with outcome. In conclusion, SUB devices are a feasible option to treat cats with UO,
associated with slow progression of chronic kidney disease and long survival time.
Positive urine culture or severe azotemia at presentation do not predict a worse
outcome
Conformity Hinders the Evolution of Cooperation on Scale-Free Networks
We study the effects of conformity, the tendency of humans to imitate locally
common behaviors, in the evolution of cooperation when individuals occupy the
vertices of a graph and engage in the one-shot Prisoner's Dilemma or the
Snowdrift game with their neighbors. Two different graphs are studied: rings
(one-dimensional lattices with cyclic boundary conditions) and scale-free
networks of the Barabasi-Albert type. The proposed evolutionary-graph model is
studied both by means of Monte Carlo simulations and an extended
pair-approximation technique. We find improved levels of cooperation when
evolution is carried on rings and individuals imitate according to both the
traditional pay-off bias and a conformist bias. More important, we show that
scale-free networks are no longer powerful amplifiers of cooperation when fair
amounts of conformity are introduced in the imitation rules of the players.
Such weakening of the cooperation-promoting abilities of scale-free networks is
the result of a less biased flow of information in scale-free topologies,
making hubs more susceptible of being influenced by less-connected neighbors.Comment: 14 pages, 11 figure
Evolution of Cooperation and Coordination in a Dynamically Networked Society
Situations of conflict giving rise to social dilemmas are widespread in society and game theory is one major way in which they can be investigated. Starting from the observation that individuals in society interact through networks of acquaintances, we model the co-evolution of the agents' strategies and of the social network itself using two prototypical games, the Prisoner's Dilemma and the Stag-Hunt. Allowing agents to dismiss ties and establish new ones, we find that cooperation and coordination can be achieved through the self-organization of the social network, a result that is nontrivial, especially in the Prisoner's Dilemma case. The evolution and stability of cooperation implies the condensation of agents exploiting particular game strategies into strong and stable clusters which are more densely connected, even in the more difficult case of the Prisoner's Dilemm
Social Dilemmas and Cooperation in Complex Networks
In this paper we extend the investigation of cooperation in some classical
evolutionary games on populations were the network of interactions among
individuals is of the scale-free type. We show that the update rule, the payoff
computation and, to some extent the timing of the operations, have a marked
influence on the transient dynamics and on the amount of cooperation that can
be established at equilibrium. We also study the dynamical behavior of the
populations and their evolutionary stability.Comment: 12 pages, 7 figures. to appea
Mutual Trust and Cooperation in the Evolutionary Hawks-Doves Game
Using a new dynamical network model of society in which pairwise interactions
are weighted according to mutual satisfaction, we show that cooperation is the
norm in the Hawks-Doves game when individuals are allowed to break ties with
undesirable neighbors and to make new acquaintances in their extended
neighborhood. Moreover, cooperation is robust with respect to rather strong
strategy perturbations. We also discuss the empirical structure of the emerging
networks, and the reasons that allow cooperators to thrive in the population.
Given the metaphorical importance of this game for social interaction, this is
an encouraging positive result as standard theory for large mixing populations
prescribes that a certain fraction of defectors must always exist at
equilibrium.Comment: 23 pages 12 images, to appea
Evolution of Coordination in Social Networks: A Numerical Study
Coordination games are important to explain efficient and desirable social
behavior. Here we study these games by extensive numerical simulation on
networked social structures using an evolutionary approach. We show that local
network effects may promote selection of efficient equilibria in both pure and
general coordination games and may explain social polarization. These results
are put into perspective with respect to known theoretical results. The main
insight we obtain is that clustering, and especially community structure in
social networks has a positive role in promoting socially efficient outcomes.Comment: preprint submitted to IJMP
Evolutionary Games on Networks and Payoff Invariance Under Replicator Dynamics
The commonly used accumulated payoff scheme is not invariant with respect to
shifts of payoff values when applied locally in degree-inhomogeneous population
structures. We propose a suitably modified payoff scheme and we show both
formally and by numerical simulation, that it leaves the replicator dynamics
invariant with respect to affine transformations of the game payoff matrix. We
then show empirically that, using the modified payoff scheme, an interesting
amount of cooperation can be reached in three paradigmatic non-cooperative
two-person games in populations that are structured according to graphs that
have a marked degree inhomogeneity, similar to actual graphs found in society.
The three games are the Prisoner's Dilemma, the Hawks-Doves and the Stag-Hunt.
This confirms previous important observations that, under certain conditions,
cooperation may emerge in such network-structured populations, even though
standard replicator dynamics for mixing populations prescribes equilibria in
which cooperation is totally absent in the Prisoner's Dilemma, and it is less
widespread in the other two games.Comment: 20 pages, 8 figures; to appear on BioSystem
Evolution of Cooperation and Coordination in a Dynamically Networked Society
Situations of conflict giving rise to social dilemmas are widespread in
society and game theory is one major way in which they can be investigated.
Starting from the observation that individuals in society interact through
networks of acquaintances, we model the co-evolution of the agents' strategies
and of the social network itself using two prototypical games, the Prisoner's
Dilemma and the Stag Hunt. Allowing agents to dismiss ties and establish new
ones, we find that cooperation and coordination can be achieved through the
self-organization of the social network, a result that is non-trivial,
especially in the Prisoner's Dilemma case. The evolution and stability of
cooperation implies the condensation of agents exploiting particular game
strategies into strong and stable clusters which are more densely connected,
even in the more difficult case of the Prisoner's Dilemma.Comment: 18 pages, 14 figures. to appea
Resolution of the stochastic strategy spatial prisoner's dilemma by means of particle swarm optimization
We study the evolution of cooperation among selfish individuals in the
stochastic strategy spatial prisoner's dilemma game. We equip players with the
particle swarm optimization technique, and find that it may lead to highly
cooperative states even if the temptations to defect are strong. The concept of
particle swarm optimization was originally introduced within a simple model of
social dynamics that can describe the formation of a swarm, i.e., analogous to
a swarm of bees searching for a food source. Essentially, particle swarm
optimization foresees changes in the velocity profile of each player, such that
the best locations are targeted and eventually occupied. In our case, each
player keeps track of the highest payoff attained within a local topological
neighborhood and its individual highest payoff. Thus, players make use of their
own memory that keeps score of the most profitable strategy in previous
actions, as well as use of the knowledge gained by the swarm as a whole, to
find the best available strategy for themselves and the society. Following
extensive simulations of this setup, we find a significant increase in the
level of cooperation for a wide range of parameters, and also a full resolution
of the prisoner's dilemma. We also demonstrate extreme efficiency of the
optimization algorithm when dealing with environments that strongly favor the
proliferation of defection, which in turn suggests that swarming could be an
important phenomenon by means of which cooperation can be sustained even under
highly unfavorable conditions. We thus present an alternative way of
understanding the evolution of cooperative behavior and its ubiquitous presence
in nature, and we hope that this study will be inspirational for future efforts
aimed in this direction.Comment: 12 pages, 4 figures; accepted for publication in PLoS ON