The book makes a great deal of Tess's ancient family bloodline. It's not something Tess herself cares much about, but Parson Tringham finds the subject very interesting, Jack Durbeyfield becomes incredibly conceited about it, and even Angel Clare thinks it is important. Angel thinks all these grand, old families have become exhausted. It all seems very odd for rational people to hold such store by it, as if the quality of nobility, not merely land and titles, is passed on intransmutable with the Y chromosone across the generations. Tess does not have a Y chromosone so she wouldn't inherit it anyway. At one point Tess says to herself that she is half her mother and gets her looks from her. I thought Hardy was poking fun at the attitude, but then Tess does seem to inherit some of her ancestors' traits. There's the slight resemblance to the portraits in the d'Urbervilles old house, the legend of the d'Urberville coach, and Tess's occasional flashes of aggression recalling the knights of old. By the end I wondered whether Hardy thought there was something in it.
BTW, according to my father, I am descended from a nobleman titled Sir Willoughby de Broke.