Origins of Hutu, Tutsi and Twa phenotype, genotype, cultural memory of inhabitants of Rwanda, archeology, and linguistics. Most Tutsis and Hutus carry the E1b1a paternal haplogroup, which is common among Bantu populations. More recent studies have de-emphasized physical appearance, such as height and nose width, in favor of examining blood factors, the presence of the sickle cell trait, lactose intolerance in adults, and other genotype expressions. Excoffier et al. (1987) found that the Tutsi and Hima, despite being surrounded by Bantu populations, are "closer genetically to Cushites and Ethiosemites". Another study concluded that, while the sickle cell trait among the Rwandan Hutu was comparable to that
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