James Michener's Chesapeake shows the long, complex history of families as they deal with four hundred years of change in developing America.
The Turlock family represent the poverty of so many families in the time. Without a wealth base from their founding, or a "noble" bloodline to draw on for favors, the Turlocks must make their own success without help from the outside. Instead of their hardships coming from economic and cultural change, the Turlocks fight with nature for survival every day; they hunt and fish for food, and live in a single cabin. They are not accepted by society, and are not "moral" in the religious sense applied by the conservative Steed family; they smuggle, bootleg, and have little compunction about violence for necessity. This is less an indictment than it is a simple fact about the time; with no inherited wealth, the Turlocks have a bred instinct for survival, both in culture and nature.
The Turlock family's most vital roles in the book are to contrast with the richer families, and to show the base interaction with the Native American tribes living in the same area. Since they lived in similar situations, the Turlocks and the Natives are comparable in their needs and actions; they also lack much of the prejudice felt against the Natives by the richer families, and in fact they intermarry with one of the tribes, helping to prolong the Native bloodlines while the tribes slowly die out.