and domestic chicks) also innately avoid conspicuously coloured objects, as demonstrated using mealworms painted yellow and black to resemble wasps, with dull green controls. This implies that warning coloration works at least in part by stimulating the evolution of predators to encode the meaning of the warning signal, rather than by requiring each new generation to learn the signal's meaning. All of these results contradict the idea that novel, brightly coloured individuals would be more likely to be eaten or attacked by predators. Alternative hypotheses Other explanations are possible. Predators might innately fear unfamiliar forms (neophobia) long enough for them to become established, but this is likely to be only temporary. Alternatively, prey animals might be sufficiently gregarious to form clusters tight enough to enhance the warning signal. If the species was already unpalatable, predators might learn to avoid the cluster, protecting gregarious individuals with the new aposematic trait. Gregariousness would assist predators to learn to avoid unpalatable, gregarious prey. Aposematism could also be favoured in dense populations even if these are not gregarious. Another possibility is that a gene for aposematism might be recessive and located on the X chromosome. If so, predators would learn to associate the colour with unpalatability from males with the trait, while heterozygous females carry the trait until it becomes common and predators understand the signal. Well-fed predators might also ignore aposematic morphs, preferring other prey species. A further explanation is that females might prefer brighter males, so sexual selection could result in aposematic males having higher reproductive success than non-aposematic males if they can survive long enough to mate. Sexual selection is strong enough to allow seemingly maladaptive traits to persist despite other factors working against the trait. Once aposematic individuals reach a certain threshold population, for whatever reason, the predator learning process would be spread out over a larger number of individuals and therefore is less likely to wipe out the trait for warning coloration completely. If the population of aposematic individuals all originated from the same few individuals, the predator learning process would result in a stronger warning signal for surviving kin, resulting in higher inclusive fitness for the dead or injured individuals through kin selection. A theory for the evolution of aposematism posits that it arises by reciprocal selection between predators and prey, where distinctive features in prey, which could be visual or chemical, are selected by non-discriminating predators, and