How do accents develop? where do they come from?

pardon my ignorance but where exactly do you get an accent from?Now i know it has something to do with,heredity,right? you get it from your mom,your dad,etc.But where did your mother and father get it from? where did accents start originally?And if it's nothing hereditary,how do you all of a sudden get an accent?if i live in france for a year will i develop a french accent? please help me,10 pts for best answer