What evidence must be considered when determining whether or not a trait is an adaptation? (Site 1)

According to Charles Darwin's theory of evolution by natural selection, organisms that possess heritable traits that enable them to better adapt to their environment compared with other members of their species will be more likely to survive, reproduce, and pass more of their genes on to the next generation. The next generation will have the things they will need to survive and the longer the generation goes the more fetchers they will have.