What was charles darwin's theory regarding plant and animal life

He basically believed in evolution,

he said that in species, a mutation occured, 
sometimes this meant they were better adapted to survive, 
therefore they would survive, 
the others would die out,
the mutated animal/plant would reproduce,
they would pass on their gene to their offspring,

this is his theory of evolution :)

In the midwest because it has more moderate climate than the north or south west which makes farming far easier.