A core concept in Murray Bowen's family systems theory is the differentiation of self. This is the degree to which family members are differentiated from one another. According to Bowen, individuals operate along a spectrum with fusion at the lower end and differentiation at the higher end. While there is an intrinsic force that propels one to differentiate, there is at the same time a countervailing force that prevents differentiation. This emotional togetherness, or what Bowen called the undifferentiated family ego mass, preserves the status quo.
As is often the case with incest, family members are found to be undifferentiated from one another.