 In spite of their differences, however, many commonalities were brought to light by the research.Lisa and Martha are both represented as characters who, rather than lacking social skills, play "a central role within their families’ relationships" (David X. Cohen describes Lisa as "the heart of the family", Davies describes Martha as a "sort of peace-maker within her family"); "Martha’s family," the article says, "and her relationships with them, are part of the narrative that runs throughout the series", who are her constant despite the time travel aspect of the series.