3,857 research outputs found
The collapse of cooperation in evolving games
Game theory provides a quantitative framework for analyzing the behavior of
rational agents. The Iterated Prisoner's Dilemma in particular has become a
standard model for studying cooperation and cheating, with cooperation often
emerging as a robust outcome in evolving populations. Here we extend
evolutionary game theory by allowing players' strategies as well as their
payoffs to evolve in response to selection on heritable mutations. In nature,
many organisms engage in mutually beneficial interactions, and individuals may
seek to change the ratio of risk to reward for cooperation by altering the
resources they commit to cooperative interactions. To study this, we construct
a general framework for the co-evolution of strategies and payoffs in arbitrary
iterated games. We show that, as payoffs evolve, a trade-off between the
benefits and costs of cooperation precipitates a dramatic loss of cooperation
under the Iterated Prisoner's Dilemma; and eventually to evolution away from
the Prisoner's Dilemma altogether. The collapse of cooperation is so extreme
that the average payoff in a population may decline, even as the potential
payoff for mutual cooperation increases. Our work offers a new perspective on
the Prisoner's Dilemma and its predictions for cooperation in natural
populations; and it provides a general framework to understand the co-evolution
of strategies and payoffs in iterated interactions.Comment: 33 pages, 13 figure
Small games and long memories promote cooperation
Complex social behaviors lie at the heart of many of the challenges facing
evolutionary biology, sociology, economics, and beyond. For evolutionary
biologists in particular the question is often how such behaviors can arise
\textit{de novo} in a simple evolving system. How can group behaviors such as
collective action, or decision making that accounts for memories of past
experience, emerge and persist? Evolutionary game theory provides a framework
for formalizing these questions and admitting them to rigorous study. Here we
develop such a framework to study the evolution of sustained collective action
in multi-player public-goods games, in which players have arbitrarily long
memories of prior rounds of play and can react to their experience in an
arbitrary way. To study this problem we construct a coordinate system for
memory- strategies in iterated -player games that permits us to
characterize all the cooperative strategies that resist invasion by any mutant
strategy, and thus stabilize cooperative behavior. We show that while larger
games inevitably make cooperation harder to evolve, there nevertheless always
exists a positive volume of strategies that stabilize cooperation provided the
population size is large enough. We also show that, when games are small,
longer-memory strategies make cooperation easier to evolve, by increasing the
number of ways to stabilize cooperation. Finally we explore the co-evolution of
behavior and memory capacity, and we find that longer-memory strategies tend to
evolve in small games, which in turn drives the evolution of cooperation even
when the benefits for cooperation are low
The evolution of complex gene regulation by low specificity binding sites
Transcription factor binding sites vary in their specificity, both within and
between species. Binding specificity has a strong impact on the evolution of
gene expression, because it determines how easily regulatory interactions are
gained and lost. Nevertheless, we have a relatively poor understanding of what
evolutionary forces determine the specificity of binding sites. Here we address
this question by studying regulatory modules composed of multiple binding
sites. Using a population-genetic model, we show that more complex regulatory
modules, composed of a greater number of binding sites, must employ binding
sites that are individually less specific, compared to less complex regulatory
modules. This effect is extremely general, and it hold regardless of the
regulatory logic of a module. We attribute this phenomenon to the inability of
stabilising selection to maintain highly specific sites in large regulatory
modules. Our analysis helps to explain broad empirical trends in the yeast
regulatory network: those genes with a greater number of transcriptional
regulators feature by less specific binding sites, and there is less variance
in their specificity, compared to genes with fewer regulators. Likewise, our
results also help to explain the well-known trend towards lower specificity in
the transcription factor binding sites of higher eukaryotes, which perform
complex regulatory tasks, compared to prokaryotes
Evolutionary consequences of behavioral diversity
Iterated games provide a framework to describe social interactions among
groups of individuals. Recent work stimulated by the discovery of
"zero-determinant" strategies has rapidly expanded our ability to analyze such
interactions. This body of work has primarily focused on games in which players
face a simple binary choice, to "cooperate" or "defect". Real individuals,
however, often exhibit behavioral diversity, varying their input to a social
interaction both qualitatively and quantitatively. Here we explore how access
to a greater diversity of behavioral choices impacts the evolution of social
dynamics in finite populations. We show that, in public goods games, some
two-choice strategies can nonetheless resist invasion by all possible
multi-choice invaders, even while engaging in relatively little punishment. We
also show that access to greater behavioral choice results in more "rugged "
fitness landscapes, with populations able to stabilize cooperation at multiple
levels of investment, such that choice facilitates cooperation when returns on
investments are low, but hinders cooperation when returns on investments are
high. Finally, we analyze iterated rock-paper-scissors games, whose
non-transitive payoff structure means unilateral control is difficult and
zero-determinant strategies do not exist in general. Despite this, we find that
a large portion of multi-choice strategies can invade and resist invasion by
strategies that lack behavioral diversity -- so that even well-mixed
populations will tend to evolve behavioral diversity.Comment: 26 pages, 4 figure
Under-dominance constrains the evolution of negative autoregulation in diploids
Regulatory networks have evolved to allow gene expression to rapidly track
changes in the environment as well as to buffer perturbations and maintain
cellular homeostasis in the absence of change. Theoretical work and empirical
investigation in Escherichia coli have shown that negative autoregulation
confers both rapid response times and reduced intrinsic noise, which is
reflected in the fact that almost half of Escherichia coli transcription
factors are negatively autoregulated. However, negative autoregulation is
exceedingly rare amongst the transcription factors of Saccharomyces cerevisiae.
This difference is all the more surprising because E. coli and S. cerevisiae
otherwise have remarkably similar profiles of network motifs. In this study we
first show that regulatory interactions amongst the transcription factors of
Drosophila melanogaster and humans have a similar dearth of negative
autoregulation to that seen in S. cerevisiae. We then present a model
demonstrating that this fundamental difference in the noise reduction
strategies used amongst species can be explained by constraints on the
evolution of negative autoregulation in diploids. We show that regulatory
interactions between pairs of homologous genes within the same cell can lead to
under-dominance - mutations which result in stronger autoregulation, and
decrease noise in homozygotes, paradoxically can cause increased noise in
heterozygotes. This severely limits a diploid's ability to evolve negative
autoregulation as a noise reduction mechanism. Our work offers a simple and
general explanation for a previously unexplained difference between the
regulatory architectures of E. coli and yeast, Drosophila and humans. It also
demonstrates that the effects of diploidy in gene networks can have
counter-intuitive consequences that may profoundly influence the course of
evolution
Local-time asymmetries in the Venus thermosphere
Our current understanding of the global structure and dynamics of the Venus thermosphere is embodied in models such as the Venus Thermospheric General Circulation Model (VTGCM) and empirical composition models such as VIRA and VTS3. We have completed an analysis of ultraviolet images of Venus at 130 nm acquired by the Pioneer Venus Orbiter Ultraviolet Spectrometer (PVOUVS). We have examined 97 images spanning the 10-year period between 1980 and 1990, and have developed a technique for global radiative transfer modeling with which we create synthetic models of each image analyzed. We have developed a hypothesis for understanding the persistent local-time asymmetry observed as a signature of vertically propagating internal gravity waves interacting with the thermospheric SS-AS circulation. This hypothesis is presented
Group reciprocity and the evolution of stereotyping
Funding: A.J.S. is supported by the John Templeton Foundation for funding (grant no. 62281). N.R. is supported by the Royal Society and the Leverhulme Trust.Stereotypes are generalized beliefs about groups of people, which are used to make decisions and judgements about them. Although such heuristics can be useful when decisions must be made quickly, or when information is lacking, they can also serve as the basis for prejudice and discrimination. In this paper, we study the evolution of stereotypes through group reciprocity. We characterize the warmth of a stereotype as the willingness to cooperate with an individual based solely on the identity of the group they belong to. We show that when stereotype groups are large, such group reciprocity is less likely to evolve, and stereotypes tend to be negative. We also show that, even when stereotypes are broadly positive, individuals are often overly pessimistic about the willingness of those they stereotype to cooperate. We then show that the tendency for stereotyping itself to evolve is driven by the costs of cognition, so that more people are stereotyped with greater coarseness as costs increase. Finally we show that extrinsic ‘shocks’, in which the benefits of cooperation are suddenly reduced, can cause stereotype warmth and judgement bias to turn sharply negative, consistent with the view that economic and other crises are drivers of out-group animosity.Publisher PDFPeer reviewe
The evolvability of cooperation under local and non-local mutations
Funding: J.B.P. acknowledges funding from the Burroughs Wellcome Fund, the David and Lucile Packard Foundation, US Department of the Interior Grant D12AP00025, and Foundational Questions in Evolutionary Biology Fund Grant RFP-12-16.We study evolutionary dynamics in a population of individuals engaged in pairwise social interactions, encoded as iterated games. We consider evolution within the space of memory-1strategies, and we characterize all evolutionary robust outcomes, as well as their tendency to evolve under the evolutionary dynamics of the system. When mutations are restricted to be local, as opposed to non-local, then a wider range of evolutionary robust outcomes tend to emerge, but mutual cooperation is more difficult to evolve. When we further allow heritable mutations to the player’s investment level in each cooperative interaction, then co-evolution leads to changes in the payoff structure of the game itself and to specific pairings of robust games and strategies in the population. We discuss the implications of these results in the context of the genetic architectures that encode how an individual expresses its strategy or investment.Publisher PDFPeer reviewe
Small groups and long memories promote cooperation
Complex social behaviors lie at the heart of many of the challenges facing evolutionary biology, sociology, economics, and beyond. For evolutionary biologists the question is often how group behaviors such as collective action, or decision making that accounts for memories of past experience, can emerge and persist in an evolving system. Evolutionary game theory provides a framework for formalizing these questions and admitting them to rigorous study. Here we develop such a framework to study the evolution of sustained collective action in multi-player public-goods games, in which players have arbitrarily long memories of prior rounds of play and can react to their experience in an arbitrary way. We construct a coordinate system for memory-m strategies in iterated n-player games that permits us to characterize all cooperative strategies that resist invasion by any mutant strategy, and stabilize cooperative behavior. We show that, especially when groups are small, longer-memory strategies make cooperation easier to evolve, by increasing the number of ways to stabilize cooperation. We also explore the co-evolution of behavior and memory. We find that even when memory has a cost, longer-memory strategies often evolve, which in turn drives the evolution of cooperation, even when the benefits for cooperation are low.Publisher PDFPeer reviewe
Inequality, identity, and partisanship : how redistribution can stem the tide of mass polarization
The form of political polarization where citizens develop strongly negative attitudes toward out-party members and policies has become increasingly prominent across many democracies. Economic hardship and social inequality, as well as intergroup and racial conflict, have been identified as important contributing factors to this phenomenon known as “affective polarization.” Research shows that partisan animosities are exacerbated when these interests and identities become aligned with existing party cleavages. In this paper, we use a model of cultural evolution to study how these forces combine to generate and maintain affective political polarization. We show that economic events can drive both affective polarization and the sorting of group identities along party lines, which, in turn, can magnify the effects of underlying inequality between those groups. But, on a more optimistic note, we show that sufficiently high levels of wealth redistribution through the provision of public goods can counteract this feedback and limit the rise of polarization. We test some of our key theoretical predictions using survey data on intergroup polarization, sorting of racial groups, and affective polarization in the United States over the past 50 y.PostprintPeer reviewe
- …