. In 1969, McDowall compiled studies on marine animals that seem to show occurrence of lunar rhythms and their respective mechanisms to adapt with their environmental changes. Some scientists argue that certain animal behavior is a response to lunar stimuli (e.g. Moonlight) while others reason that the rhythmic activity has adapted to the long-term cycles and continue to persist because of "biological clock" (McDowall 1969). Some observations, maybe due to lack of study during or maybe due to complexity, have no causal mechanism to explain rhythmic behaviors.