The<unk>  is composed of highly specialized,<unk> ic cells and processes that eliminate pathogenic challenges. Thought to have arisen in the first jawed vertebrates, the<unk>  or "specific"<unk><unk>  is activated by the “non-specific” and evolutionarily older innate<unk><unk>  (which is the major<unk>  of host defense against pathogens in nearly all other living things). The<unk><unk>  response provides the vertebrate<unk><unk>  with the ability to recognize and remember specific pathogens (to generate<unk> ty), and to mount stronger attacks each time the pathogen is encountered. It is<unk> <unk> ty because the body's<unk><unk>  prepares itself for future challenges.
The<unk>  is highly adaptable because of somatic hypermutation (a process of accelerated somatic mutations), and V(D)J recombination (an irreversible genetic recombination of antigen receptor gene segments). This mechanism allows a small number of genes to generate a vast number of different antigen receptors, which are then uniquely expressed on each individual lymphocyte. Because the gene rearrangement leads to an irreversible change in the DNA of each cell, all of the progeny of that cell will then inherit genes encoding the same receptor specificity, including the Memory B cells and Memory T cells that are the keys to long-lived specific<unk> ty.
Adaptive immune system
Innate immune system
Complement system
Visual perception
Haptic perception
Muscle memory
Hematopoiesis
Cellular memory