survival of the fittest united states theory

A defect in the second phase can trigger massive inflammation, tissue damage and death. A deficiency in the first phase can allow uncontrolled growth of the infectious agent, such as a virus or bacteria. This is followed by phase 2, during which immune cells called regulatory T cells suppress inflammation so that the infected tissues can completely heal. When an infectious agent attacks, the body begins phase 1, which promotes inflammation – a state in which a variety of immune cells gather at the site of infection to destroy the pathogen.

Failure in either can have significant consequences.Īn effective immune response against an infectious agent rests in the delicate balance of two phases of action. To reach a destination safely, you need both an accelerator (phase 1) and a brake (phase 2) that are functioning well. Birds with the right beaks were defined as the fittest. Darwin recognized that finches with beaks adapted to the specific food sources present on an island were more likely to survive and pass their genes to the next generation.

Survival of the fittest united states theory