= Solution
\b[Apparent resemblance generates competing hypotheses, not a diagnosis of <mimicry>. Establishing receiver-relevant similarity, evolutionary history and the <biological fitness> effect of resemblance are separate tasks.] Shared ancestry, shared developmental responses and similar ecological demands may all contribute, and the origin of a pattern need not be the same as the process currently maintaining it.
First establish that the sampled individuals represent distinct <species> and comparable life stages and sexes. Voucher records, repeated observations, morphology and independent genetic evidence help distinguish <species> from geographical forms or sexually different members of one <species>. Sampling should span localities, seasons and within-species variation, since choosing only strikingly similar specimens exaggerates community-wide resemblance. For each individual, record dorsal and ventral patterns, size, resting posture, flight behaviour, microhabitat and activity time. An identical-looking patch in a photograph may rarely be exposed to the same receiver in nature.
Similarity must then be measured for plausible receivers. Predatory <birds> and butterfly mates need not share human <colour vision>. Calibrated <reflectance> measurements across visible and ultraviolet wavelengths, natural illumination and relevant backgrounds can support a <colour vision model>. A simplified relative <receptor quantum catch> is:
$$
Q_i\propto\int L(\lambda)R(\lambda)S_i(\lambda)\,d\lambda,
$$
where $L$ is illumination, $R$ surface <reflectance> and $S_i$ the effective <spectral sensitivity> of receptor class $i$. The comparison should include <receptor noise> and spatial resolution, because two spectrally distinguishable patches may be unresolved at attack distance. An apparent human match may conceal an ultraviolet or spatial difference. Conversely, experimentally demonstrated <predator> generalization can establish functional similarity despite a difference obvious to a human. A model predicts discrimination; behavioural tests verify whether the animal actually uses it.
One hypothesis is retention of an ancestral pattern through <biological homology>. Infer relationships from many independent genomic regions, then reconstruct pattern changes with uncertainty on the resulting <phylogenetic tree>. Resemblance concentrated among close relatives is compatible with retention. Similarity among distant relatives, especially matching different local patterns in different places, supports repeated change, although uncertainty in ancestral states must be retained. A single wing-pattern <gene tree> cannot serve as the independent <species> history when that very region might have crossed <species> boundaries.
A second hypothesis is <Müllerian mimicry>. If several <species> are defended and share <predators>, a common warning pattern can reduce the number of individuals attacked while <predators> learn avoidance. A local <mimicry ring> is predicted, with newcomers to an unfamiliar pattern suffering more attacks. Measure defence rather than infer it from colour: chemical assays, controlled feeding responses and subsequent <predator> behaviour address different components of <palatability>. <predators> from different localities may have different experience, so both naive and experienced receivers are informative. Several defended <species> can differ in defence strength; their interaction need not fit a perfectly symmetric mutual benefit.
A third hypothesis is <Batesian mimicry>, in which a relatively undefended <species> gains protection by resembling a defended model. This predicts protection dependent on the model's presence, abundance and the receiver's experience. A resemblance experiment should therefore vary both visual matching and the frequency or density of defended and undefended <prey>. A palatable mimic that becomes too common can weaken learned avoidance, whereas sharing a well-defended signal can reinforce it. These are ecological predictions to test, not a rule that each natural assemblage falls into one simple category. Defence varies with diet, age and the <predator> used in the assay.
The critical causal experiment changes the signal while controlling the rest of the <prey>. Artificial <prey> or wing models can independently vary colour and geometry against a standardized food reward. Randomized placement and position changes control background and location; handling and paint controls are needed with live butterflies. Record detection, attack and rejection separately: fewer missing <prey> can reflect poor detection rather than avoidance after recognition. Camera records help identify actual <predators> and distinguish attack from weather damage or removal by other animals. Artificial models lack movement and some chemical information, so their results should be checked against observations of live <prey> where feasible.
A field precedent is the release of different <Heliconius cydno> colour morphs into communities with different abundant co-models. Survival patterns supported an advantage to local matching, and the experiment also examined the prediction that this disadvantage should decrease with increased release density. <Three-butterfly system provides a field test of müllerian mimicry by Durrell D. Kapan>[Nature 409, pp. 338–340; H. cydno release experiments, local co-models and release density]{ref} This is more informative than simply mapping similar butterflies in the same forest. However, disappearance after release can include dispersal and unequal detectability; recapture effort, movement observations and attack evidence are needed when adapting such a design. Replication belongs at the site or independently manipulated community level, rather than treating every observation within one site as an independent community comparison.
Other ecological explanations deserve distinct predictions. Shared <crypsis> could make <species> match the same leaves, bark or light environment without resembling one another as defended models. Test detection against matched and mismatched backgrounds, separating the visibility of the <prey> from a <predator>'s willingness to consume it. Shared <thermoregulation>[thermoregulatory] demands could favour similar absorption properties; temperature and performance measurements would then be relevant. Similar mate-detection environments could favour similar signals, but <mate preference> experiments must establish the relevant receiver and show how <species> avoid reproductive confusion. These mechanisms can coexist with defensive <mimicry>.
A common developmental or environmental cause is another possibility. Rear offspring from different populations and <species> in standardized and experimentally varied conditions, controlling larval diet, temperature and age. Persistence of differences under common rearing supports inherited contributions; condition-dependent convergence supports <phenotypic plasticity>. Crosses and <quantitative trait locus mapping> can then test the <genetic architecture> of patterning. Work on <Optix> in <Heliconius> combined mapping, expression and population comparisons to identify a shared regulator of red wing patterning. <optix Drives the Repeated Convergent Evolution of Butterfly Wing Pattern Mimicry by Robert D. Reed and others>[Science 333, pp. 1137–1141; mapping, expression and population genetics of red wing patterning]{ref} Use of the same developmental <gene> does not by itself prove a single recent origin of the pattern, nor prove that resemblance is adaptive.
Finally, adaptive <introgression> could transfer a pattern-associated region between <species>. Genome-wide ancestry should be compared with local ancestry around pattern regions, testing alternatives such as <incomplete lineage sorting>. The <Heliconius> genome study found evidence of exchange associated with mimetic adaptations among lineages. <Butterfly genome reveals promiscuous exchange of mimicry adaptations among species by The Heliconius Genome Consortium>[Nature 487, pp. 94–98; genomic comparisons and introgression around mimicry loci]{ref} This concerns the route by which a useful pattern is acquired; selection by <predators> can still explain its maintenance. \b[The strongest explanation combines receiver-specific similarity, a tested ecological benefit and an independently supported developmental and evolutionary history; neither human resemblance nor a shared pattern-associated <gene> supplies all three.]
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