The information contained in social systems, and the part of it that animals actually possess, is a driver of the evolution of sociality, cognition, and animal culture . However, it is difficult to detect how much information individuals actually have about their social worlds. Even when information can be detected, differences in methodology make cross-species comparisons difficult. We present a new method for detecting social information in dominance hierarchies, that infers individual-level rules for aggression based on how aggression decisions are influenced by differences in social rank. We apply this method to 172 social groups across 85 species in 22 orders. By looking for heuristics that depend upon rank information, we can back-infer the types of information individuals possess about the macro-level properties of their group. Summary measures of these heuristics then place groups within a taxonomy, providing a biologically-relevant "social assay" to quantify the amount of social information and to identify consensus strategies at the group level . The majority of animal groups in our dataset (112 groups, 65 \%) follow a downward heuristic to structure their fights, spreading aggression relatively equally across lower-ranked opponents but 50 groups (29\%) use strategies that are indicative of more detailed rank information . Strategies are not phylogenetically constrained and  groups within the same species can use different strategies, indicating that the choice of heuristics may be contextual and that the structuring of aggression by social information should not be considered a fixed characteristic . Instead, individuals may be able to plastically respond to local conditions by increasing or decreasing the complexity of their strategies . Our approach provides new opportunities to study the use of social information  across species and the evolution of social complexity and cognition.
Members of a social species need to make appropriate decisions about who, how, and when to interact with others in their group . However, it has been difficult for researchers to detect the inputs to these decisions and, in particular, how much information individuals actually have about their social context. We present a new method that can serve as a social assay to quantify how patterns of aggression depend upon information about the ranks of individuals within social dominance hierarchies. Applied to existing data on aggression in 172 social groups across 85 species in 23 orders, it reveals three main patterns of rank-dependent social dominance: the downward heuristic (aggress uniformly against lower-ranked opponents), close competitors (aggress against opponents ranked slightly below self), and bullying (aggress against opponents ranked much lower than self) . The majority of the groups (133 groups, 77 \%) follow a downward heuristic , but a significant minority (38 groups, 22\%) show more complex social dominance patterns (close competitors or bullying) consistent with higher levels of social information use. These patterns are not phylogenetically constrained and different groups within the same species can use different patterns, suggesting that heuristics use may depend on context and the structuring of aggression by social information should not be considered a fixed characteristic of a species . Our approach provides new opportunities to study the use of social information within and across species and the evolution of social complexity and cognition.
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The information contained in social systems, and the part of it that animals actually possess, is a driver of the evolution of sociality, cognition, and animal culture
Members of a social species need to make appropriate decisions about who, how, and when to interact with others in their group
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is difficult to detect
has been difficult for researchers to detect the inputs to these decisions and, in particular,
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worlds. Even when information can be detected, differences in methodology make cross-species comparisons difficult.
context.
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for detecting social information in dominance hierarchies, that infers individual-level rules for aggression based on how aggression decisions are influenced by differences in social rank. We apply this method to
that can serve as a social assay to quantify how patterns of aggression depend upon information about the ranks of individuals within social dominance hierarchies. Applied to existing data on aggression in
R
22 orders. By looking for heuristics that depend upon rank information, we can back-infer the types of information individuals possess about the macro-level properties of their group. Summary measures of these heuristics then place groups within a taxonomy, providing a biologically-relevant "social assay" to quantify the amount of social information and to identify consensus strategies at the group level
23 orders, it reveals three main patterns of rank-dependent social dominance: the downward heuristic (aggress uniformly against lower-ranked opponents), close competitors (aggress against opponents ranked slightly below self), and bullying (aggress against opponents ranked much lower than self)
R
animal groups in our dataset (112 groups, 65
the groups (133 groups, 77
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to structure their fights, spreading aggression relatively equally across lower-ranked opponents but 50 groups (29\%) use strategies that are indicative of more detailed rank information . Strategies
, but a significant minority (38 groups, 22\%) show more complex social dominance patterns (close competitors or bullying) consistent with higher levels of social information use. These patterns
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different
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strategies, indicating that the choice of heuristics may be contextual and that
patterns, suggesting that heuristics use may depend on context and
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. Instead, individuals may be able to plastically respond to local conditions by increasing or decreasing the complexity of their strategies
of a species
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within and