Evolutionary Immunology
Study of the immune system in extant species is capable of giving us a key understanding of the evolution of species and the immune system.
Different types of organisms have different types of immune systems: single-celled organisms use phagocytosis; arthropods use circulating antimicrobial peptides; and vertebrates use both the aforementioned methods as well as lymphatic systems. Every organism living today has an immune system that has evolved to be capable of protecting it from most forms of harm; those organisms that did not adapt their immune systems to external threats are no longer around to be observed.
Insects and other arthropods, while not possessing true adaptive immunity, show highly evolved systems of innate immunity, and are additionally protected from external injury (and exposure to pathogens) by their chitinous shells. Plants also use forms of innate immunity.
Read more about this topic: Immunology
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