The performance of natural behavior is commonly used as a criterion in the determination of animal welfare. This is still true, despite many authors having demonstrated that it is not a necessary component of welfare –some natural behaviors may decrease welfare, while some unnatural behaviors increase it. Here I analyze why this idea persists, and what effects it may have. I argue that the disagreement underlying this debate on natural behavior is not one about which conditions affect welfare, but a deeper conceptual disagreement about what the state of welfare actually consists of. Those advocating natural behavior typically take a “teleological” view of welfare, in which naturalness is fundamental to welfare, while opponents to the criter...