48 research outputs found
Evolution of Fairness in the Not Quite Ultimatum Game
The Ultimatum Game (UG) is an economic game where two players (proposer and
responder) decide how to split a certain amount of money. While traditional
economic theories based on rational decision making predict that the proposer
should make a minimal offer and the responder should accept it, human subjects
tend to behave more fairly in UG. Previous studies suggested that extra
information such as reputation, empathy, or spatial structure is needed for
fairness to evolve in UG. Here we show that fairness can evolve without
additional information if players make decisions probabilistically and may
continue interactions when the offer is rejected, which we call the Not Quite
Ultimatum Game (NQUG). Evolutionary simulations of NQUG showed that the
probabilistic decision making contributes to the increase of proposers' offer
amounts to avoid rejection, while the repetition of the game works to
responders' advantage because they can wait until a good offer comes. These
simple extensions greatly promote evolution of fairness in both proposers'
offers and responders' acceptance thresholds.Comment: 14 pages, 3 figure
Evolution of Human-like Social Grooming Strategies regarding Richness and Group Size
Human beings tend to cooperate with close friends, therefore they have to
construct strong social relationships to recieve cooperation from others.
Therefore they should have acquired their strategies of social relationship
construction through an evolutionary process. The behavior of social
relationship construction is know as "social grooming." In this paper, we show
that there are four classes including a human-like strategy in evolutionary
dynamics of social grooming strategies based on an evolutionary game
simulation. Social relationship strengths (as measured by frequency of social
grooming) often show a much skewed distribution (a power law distribution). It
may be due to time costs constraints on social grooming, because the costs are
too large to ignore for having many strong social relationships. Evolution of
humans' strategies of construction of social relationships may explain the
origin of human intelligence based on a social brain hypothesis. We constructed
an individual-based model to explore the evolutionary dynamics of social
grooming strategies. The model is based on behavior to win over others by
strengthening social relationships with cooperators. The results of
evolutionary simulations show the four classes of evolutionary dynamics. The
results depend on total resources and the ratio of each cooperator's resource
to the number of cooperators. One of the four classes is similar to a human
strategy, i.e. the strategies based on the Yule--Simon process of power law.Comment: 21 pages, 10 figure
Network flow of mobile agents enhances the evolution of cooperation
We study the effect of contingent movement on the persistence of cooperation
on complex networks with empty nodes. Each agent plays Prisoner's Dilemma game
with its neighbors and then it either updates the strategy depending on the
payoff difference with neighbors or it moves to another empty node if not
satisfied with its own payoff. If no neighboring node is empty, each agent
stays at the same site. By extensive evolutionary simulations, we show that the
medium density of agents enhances cooperation where the network flow of mobile
agents is also medium. Moreover, if the movements of agents are more frequent
than the strategy updating, cooperation is further promoted. In scale-free
networks, the optimal density for cooperation is lower than other networks
because agents get stuck at hubs. Our study suggests that keeping a smooth
network flow is significant for the persistence of cooperation in ever-changing
societies.Comment: 7 pages, 5 figure
How mutation alters fitness of cooperation in networked evolutionary games
Cooperation is ubiquitous in every level of living organisms. It is known
that spatial (network) structure is a viable mechanism for cooperation to
evolve. Until recently, it has been difficult to predict whether cooperation
can evolve at a network (population) level. To address this problem, Pinheiro
et al. proposed a numerical metric, called Average Gradient of Selection (AGoS)
in 2012. AGoS can characterize and forecast the evolutionary fate of
cooperation at a population level. However, stochastic mutation of strategies
was not considered in the analysis of AGoS. Here we analyzed the evolution of
cooperation using AGoS where mutation may occur to strategies of individuals in
networks. Our analyses revealed that mutation always has a negative effect on
the evolution of cooperation regardless of the fraction of cooperators and
network structures. Moreover, we found that mutation affects the fitness of
cooperation differently on different social network structures.Comment: 6 pages, 5 figure
Transitions between homophilic and heterophilic modes of cooperation
Cooperation is ubiquitous in biological and social systems. Previous studies
revealed that a preference toward similar appearance promotes cooperation, a
phenomenon called tag-mediated cooperation or communitarian cooperation. This
effect is enhanced when a spatial structure is incorporated, because space
allows agents sharing an identical tag to regroup to form locally cooperative
clusters. In spatially distributed settings, one can also consider migration of
organisms, which has a potential to further promote evolution of cooperation by
facilitating spatial clustering. However, it has not yet been considered in
spatial tag-mediated cooperation models. Here we show, using computer
simulations of a spatial model of evolutionary games with organismal migration,
that tag-based segregation and homophilic cooperation arise for a wide range of
parameters. In the meantime, our results also show another evolutionarily
stable outcome, where a high level of heterophilic cooperation is maintained in
spatially well-mixed patterns. We found that these two different forms of
tag-mediated cooperation appear alternately as the parameter for temptation to
defect is increased.Comment: 16 pages, 7 figure