ABOUT ADAPTIVE IMMUNITY
The adaptive immune system first emerged in early fish and consists of lymphocytes and their products, which likely evolved from the more ancient innate immune system. As its name suggests, adaptive immunity is not preexistent to an encounter with a specific pathogen as is innate immunity. Instead, adaptive immunity develops with specificity for a pathogen when the body encounters that particular pathogen for the first time. Adaptive immunity is further distinguished from innate immunity because of a unique property: memory.