Fisherian runaway is a concept in evolutionary biology that explains how certain traits can become exaggerated over time due to sexual selection. It occurs when a preference for a specific trait in one sex leads to the development of that trait in the other sex. For example, if female peacocks prefer males with larger tail feathers, those males will be more successful in mating, leading to even larger tail feathers in future generations. This process can create a feedback loop, where the trait becomes increasingly pronounced, even if it may not provide any survival advantage. Over time, this can result in extreme characteristics, such as the elaborate plumage seen in peacocks, which may serve primarily to attract mates rather than enhance survival.