The skin group, or “yiminga” of a Tiwi is matrilineal; it is inherited from the mother and determines the marriage line. The word “yiminga”, means skin-group, totem, life, spirit, breath and pulse.
There are four skin groups, namely; “wantarringuwi” (meaning sun), “Miyartiwi” (pandanus), “Marntimapila” (stone), and “Takaringuwi” (mullet), although each has many sub groups. The skin-group into which Tiwi is born determines who they may, and may not marry. For example, a person in the Wantarringuwi group can marry someone from the Miyartiwi or Takaringuwi groups, but never someone from the Marntimapila group, or from their own group.
Today when young Tiwi rather than their parents, choose their partner, they do not choose randomly, but rather from within the permitted skin groups. When brothers and sisters reach puberty they are not allowed to be alone together, or even to sit together; these avoidance rules apply at school and even in group-photographs.