Final answer:
The Fisherian runaway model explains how sexual selection can cause the evolution of exaggerated traits, such as bright red coloration, especially if there is a preexisting sensory bias for the trait among females. This bias could be due to reasons like visibility or association with food, and can result in a 'runaway' evolutionary process where males develop brighter red features over time to attract mates.
Step-by-step explanation:
When discussing the Fisherian runaway model in the context of a preexisting sensory bias for red, we can consider an evolutionary scenario where a preference for red could be amplified due to sexual selection. The Fisherian runaway model implies that once a female preference for a certain trait, such as a red coloration, occurs, males with more pronounced red traits have a higher chance of mating. Over time, both the male trait and female preference for it can become more exaggerated, potentially leading to the development of very bright and conspicuous red coloration in males.
Applying this to a preexisting sensory bias means that if females initially prefer red due to non-sexual reasons, such as red being easier to spot or associated with food, this preference can be hijacked by sexual selection. This can lead to an evolutionary 'runaway' where males evolve increasingly brighter red features to attract mates, aligning with the females' biased sensory perception for the color red. Additionally, field tests and laboratory experiments with other species can provide evidence supporting this model, showing that individuals might prefer or avoid certain colors due to innate biases, which in turn can affect natural selection pressures on the appearance of species.