The Rwandan social system has habitually been depicted as something of a ‘dual system’ in which Tutsi are opposed to Hutu. Forgotten in this description are the country’s least numerous group, the Twa. Although Twa constitute less than 1 per cent of Rwanda’s total population and thus appear to be politically negligible, this article maintains that they were historically more important in the symbolic construction of ethnic difference than the present literature would indicate. The Twa was the first of Rwanda’s three groups to suffer practices of social exclusion, practices called kuneena batwa which continue to this day. Associated with the forest, Twa were ascribed the negativity of ‘nature’, and perceived as not fully human by other Rwandans. Later, but before the arrival of Europeans, Hutu ethnicity began to crystallize and to be negatively compared to Tutsi. European notions of biological determinism worsened these ethnogenetic processes, but it did not invent them.