Widespread multilingualism is one form of language contact. Multilingualism was more common in the past than is usually supposed[weasel words]: in early times, when most people were members of small language communities, it was necessary to know two or more languages for trade or any other dealings outside one's own town or village, and this holds good today in places of high linguistic diversity such as Sub-Saharan Africa and India. Linguist Ekkehard Wolff estimates that 50% of the population of Africa is multilingual