The evolution of a thrombin-generating system that produces a gelatinous clot to prevent the loss of blood occurred in parallel with the evolution of inflammatory responses that depend on bradykinin generation. Bioinformatics approaches that inventory the presence or absence of genes involved in these two processes support the view that both became progressively more complex during the period between the divergence of jawless fish and the appearance of mammals. Although the roots of both systems may extend to protochordates, they arose quite independently.