What evidence must be considered when determining whether or not a trait is an adaptation?

To determine if a trait is an adaptation, evidence should include its fitness benefits in the organism's environment, demonstrating improved survival or reproductive success. Comparative studies across related species can also provide insights into the evolutionary history and functional significance of the trait. Additionally, experimental manipulation or observation of the trait's effects in natural conditions can help clarify its adaptive value. Lastly, genetic and developmental pathways that contribute to the trait’s expression should be examined to understand its evolutionary origins.