Solution
= Solution
\b[Stable social actions can reflect stable states or constraints, while flexible actions can follow an unchanged decision rule. The key distinction is between the rule, its inputs and the behaviour observed.] A <social decision rule> maps perceived social information and internal state to an action. It need not involve conscious deliberation, and it need not change genetically whenever the action changes.
For example, an individual that helps when a cue exceeds a threshold follows a fixed conditional rule even if its daily actions vary. A simple <social reaction norm> is:
$$
z_i(S)=a_i+b_iS,
$$
where $S$ describes a specified social condition, $a_i$ baseline behaviour and $b_i$ responsiveness. Individuals can differ in either parameter. A stable difference in average actions does not establish that their slopes are zero; conversely, changing actions after a partner changes does not establish that the underlying rule has been relearned. Experiments should vary social conditions within individuals and compare both baselines and responses.
Selection favours responsiveness when information predicts changes in the relative benefits of actions. A partner's willingness to cooperate, current rank, resource availability or the need for a particular task can all alter those returns. Flexibility is less useful when inputs are unreliable, conditions change faster than an individual can respond, or alternative actions cannot be produced. The <cost of behavioural flexibility> can include sampling, neural processing and switching costs. A persistent environment may favour specialization, but environmental constancy alone is insufficient: social partners can still generate changing conditions.
Development and morphology can restrict the feasible alternatives. Body size, age, reproductive development and task-specific structures influence what an individual can do. Some specializations involve effectively irreversible developmental commitment, whereas others are reversible states. It is therefore necessary to measure capacity separately from willingness. An animal that remains in one role because it cannot perform another has a different explanation from an animal that could switch but currently gains more by staying. An individual's role can also be constrained by partner aggression or exclusion, so lack of observed switching need not reveal its preferred action.
<age polyethism> in <honeybees> illustrates both regularity and flexibility. Workers commonly change tasks with age, but rearing and transplant experiments showed that interactions with older workers alter behavioural development and its hormonal regulation. <Honeybee colony integration: worker-worker interactions mediate hormonally regulated plasticity in division of labor by Z. Y. Huang and Gene E. Robinson>[PNAS 89, pp. 11726–11729; worker group rearing and older-worker transplant experiments]{ref} The pattern is thus not adequately described as an inflexible age clock. Changing the social composition can change when younger workers begin foraging. A convincing test distinguishes social information from nutrition, colony size, handling and brood demand, and measures task performance rather than relying only on age or a <hormone> concentration. The colony, not every observation of a worker within it, is often the independent <experimental unit>.
Social opportunity can also change an adult's behavioural state rapidly. In <Astatotilapia burtoni>, removal of a dominant male allowed subordinate males to adopt dominance-related behaviour and coloration within minutes, accompanied by a localized immediate-early <gene> response. Stable dominant and subordinate comparison groups helped distinguish new opportunity from simply performing dominance behaviour. <Rapid Behavioral and Genomic Responses to Social Opportunity by Sabrina S. Burmeister and others>[PLoS Biology 3, e363; removal of a dominant male and behavioural and neural responses]{ref} The manipulation minimized disturbance to the focal fish. It did not establish that every component of reproductive physiology changed immediately: behaviour, <gene expression> and gonadal development operate on different timescales. A behaviourally fixed-looking subordinate can therefore possess latent flexibility that is expressed only when social constraints change.
Information acquisition and <learning> add another source of conditional behaviour. Repeated encounters can reveal partner quality, while experience can change the expected cost of aggression or <cooperation>. A <winner-loser effect> can reinforce existing social asymmetries, but prior contest outcomes are correlated with fighting ability unless experiments separate experience from pre-existing differences. Likewise, familiarity can alter interactions through recognition without requiring a complex representation of another's intentions. Testing partner-specific rules requires swapping partners or their cues while controlling location, experience and motivational state.
Stable individual differences can arise through inherited variation, persistent developmental experience or feedback between behaviour and state. An exploratory individual may gain information that makes further exploration advantageous; a dominant individual can gain resources that maintain its competitive advantage. Partners can adjust around these differences, producing <social niche specialization>. Once complementary roles are established, unilateral switching can be costly even if an alternative allocation would have been possible initially. Such stability need not imply a separate genetically fixed strategy for every role.
<animal personality> and <behavioural repeatability> describe patterns that require explanation rather than supplying one. Repeatability can be high because individuals repeatedly encounter different environments. A <common garden experiment>, repeated measurement across social contexts and controlled developmental histories help distinguish persistent environmental effects from inherited contributions. Even a heritable baseline can coexist with a highly flexible response slope. Conversely, averaging across opposite responses can hide substantial flexibility or falsely suggest that all individuals follow the same rule.
Social specialization should also be distinguished from efficiency. In ants, separately measuring task specialization and individual task performance showed that specialization did not generally predict greater efficiency. <Specialization Does Not Predict Individual Efficiency in an Ant by Anna Dornhaus>[PLoS Biology 6, e285; separately measured task specialization, efficiency and work allocation]{ref} Stable allocation can therefore reflect task availability, differences in response thresholds or social organization rather than practice-driven superiority at the chosen task. Manipulating task demand and group composition, then measuring both the individual's response and colony output, is more informative than assuming that a frequently observed specialist is the best performer.
An experimental programme should consequently manipulate the information available and the payoffs or constraints separately. Change the number or identity of partners, task demand, social rank or encounter history; use sham disturbances and within-individual comparisons where appropriate. Reversing the treatment tests whether a change is reversible, while a delayed assay tests whether it persists through <learning> or developmental modification. Pedigrees or controlled breeding can estimate inherited variation without equating it with immutability. Response latency, errors and fitness consequences matter alongside the final action, because a rule can be flexible yet too slow or inaccurate to be advantageous.
\b[Fixed and flexible social behaviour are outcomes of selection on conditional responses, information, state and feasible actions.] Strong evidence identifies which component changed. Behavioural consistency alone establishes neither genetic determination nor adaptation, and behavioural change alone establishes neither <learning> nor a changed social rule.