The population is young and predominantly rural; Rwanda has one of the youngest populations in the world, with the average age being 19 years. Rwandans are drawn from just one cultural and linguistic group, the Banyarwanda. However, within this group there are three subgroups: the Hutu, Tutsi and Twa. The Twa are a forest-dwelling pygmy people and are often considered descendants of Rwanda's earliest inhabitants. Scholars disagree on the origins of and differences between the Hutu and Tutsi; some believe differences are derived from former social castes within a single people, while others believe the Hutu and Tutsi arrived in the country separately, and from different locations. Christianity is the largest religion in the country; the principal language is Kinyarwanda, spoken by most Rwandans, with English and French serving as additional official languages. The sovereign state of Rwanda has a presidential system of government. The president is Paul Kagame of the Rwandan Patriotic Front (RPF), who has served continuously since 2000. Today, Rwanda has low levels of corruption compared with neighbouring countries, although human rights organisations report suppression of opposition groups, intimidation and restrictions on freedom of speech. The country has been governed by a strict administrative hierarchy since precolonial times; there are five provinces delineated by borders drawn in 2006. Rwanda is one of only three countries in the world with a female majority in the national parliament, the two other countries being Bolivia and Cuba.