Kerala is a state in south-western India. Most of Kerala's 34.8 million people (in 2011) are ethnically Malayalis (Malayalam speakers). Most of the Malayalam and English speaking Keralites derive their ancestry from Dravidian communities that settled in Kerala. Additional ancestries derive from millennia of trade links across the Arabian Sea, whereby people of Arab, Jewish, Syrian and other ethnicities settled in Kerala. Many of these immigrants intermarried with native Malayalam speakers resulting in formation of many Muslims and Christians in Kerala. Some Muslims and Christians thus take lineage from Middle Eastern settlers mixed with local population. Malayalam is Kerala's official language and is spoken by at least 97% of the people of Kerala; the next most common languages are English and Tamil which is spoken mainly by migrant workers from the neighbouring state of Tamil Nadu. Tulu and Kannada is spoken in northern parts of Kasaragod district, bordering Karnataka. In addition, Kerala is home to 321,000 indigenous tribal Adivasis (1.10% of the populace). Some 63% of tribals reside in the eastern districts of Wayanad (where 35.82% are tribals), Palakkad (1.02%), and Idukki (15.66%). These groups, including the Paniyars, Mooppans, Irulars, Kurumbars, and Mudugars, speak their own native languages. Cholanaikkan tribe in the Silent Valley National Park were contacted only in the 1970s and they are the most isolated tribe in the state. Population Kerala is home to 2.76% of India's population, and at 859 persons per km2; its land is three times as densely settled as the rest of India. Kerala's western coastal regions are the most densely settled with population of 2,022 persons per km2, 2.5 times the overall population density of the state, 859 persons per km2, leaving the eastern hills and mountains comparatively sparsely populated. However, Kerala's population growth rate is far lower than the national average, although Kerala's population more than doubled between 1951 and 1991 – adding 15.6 million people to reach a total of 29.1 million residents in 1991 – the population stood at 31.8 million by 2001 and 33.3 million in 2011. Kerala's people are most densely settled in the coastal region, leaving the eastern hills and mountains comparatively sparsely populated. Kerala is the second-most urbanised major state in the country with 47.7% urban population according to the 2011 Census of India. Hinduism is followed by the majority of Keralites (54.7%). The major religions followed in Kerala are Hinduism (54.7% — Hinduism in