Organs may have multiple functions

Many organs are adapted to perform more than one function and their adaptations for each are a compromise. If an organ is studied in isolation, as if it were an adaptation for only one of its functions, it may appear poorly designed.

Consider how the mouth is used for feeding and breathing in different groups of tetrapods. The earliest tetrapods, some modern reptiles, and all modern amphibians, lack a secondary palate and have only a limited ability to eat and breathe simultaneously. A boa constrictor, for example, has to stop breathing while it goes through the complex motions of swallowing its prey - a process that can take hours. The mouth of any such species that cannot breathe while it is feeding may, if it is judged only as an adaptation for feeding, appear inefficient compared with the mammalian system; the snake's mouth is a compromised adaptation for feeding. Of the reptilian groups, only crocodiles (pictured opposite) have a full secondary palate like mammals and reptilian feeding systems can be understood as compromised in varying degrees by the need to breathe.

Trade-offs do not only exist in organ systems. In behavior, an animal has to allocate its time between different activities, for example the time allocated to foraging might be compromised by the need to spend time on other demands.

The adaptations of organisms are a set of trade-offs between multiple functions, multiple activities, and the possibilities of the present and the future. If a character is viewed in isolation it will often seem poorly adapted; but the correct standard for assessing an adaptation is its contribution to the organism's fitness in all the functions it is employed in, through the whole of the organism's life.