No, Thumbsucking is not Hereditary. It is a "childhood body-focused behavior". Though there are some people who believe thumb sucking is hereditary. Yet, no "thumb-sucking gene" has been found. However, a Japanese study involving 1,131 pairs of twins found that finger-sucking behavior was strongly influenced by genetics in 66% of male twins and 50% of female twins, as well as nail-biting behavior, in 50% of both males and females. People have long believed thumb-sucking behavior runs in families. Recently, some studies have supported this belief. According to an Austrian study that examined the families of children with eating disorders, thumb sucking was more common in children from certain types of families than those from other types of families.