Many bacterial pathogens produce to evade phagocytosis.

Mucoid capsule

Explanation:

A mucoid capsule imparts slippery outer surface to the bacterial cells. The slippery mucoid capsule does not allow the phagocytic cells of the host organisms to contact the bacterium and thereby prevents phagocytosis.

Some of the pathogenic bacteria that evade phagocytosis by the production of the mucoid capsule are Streptococcus pneumoniae, Neisseria meningitides, etc.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".