Hutu and 14% of residents in Rwanda and Burundi, respectively. The Twa pygmies, the smallest of the two countries' principal populations, also share language and culture with the Hutu and Tutsi. However, they are distinguished by a considerably shorter stature. The Hutu are believed to have first emigrated to the Great Lake region from West Africa in the great Bantu expansion. Various theories have emerged to explain the purported physical differences between them and their fellow Bantu-speaking neighbors, the Tutsi. One such thesis, largely based on oral tradition, posits that the Tutsi experienced some admixture with or were partially descended from
Rwandan genocide or simply having a "Tutsi appearance". The RPF was making slow but steady gains in the north and east of the country, ending the killings in each area occupied. The genocide was effectively ended during April in areas of Ruhengeri, Byumba, Kibungo and Kigali provinces. The killings ceased during April in the "akazu" heartlands of western Ruhengeri and Gisenyi, as almost every Tutsi had been eliminated. Large numbers of Hutu in the RPF conquered areas fled, fearing retribution for the genocide; 500,000 Kibungo residents walked over the bridge at Rusumo Falls, into Tanzania, in a few days at the end