All of the world's languages are descended from more ancient languages spoken thousands of years ago. Many languages that we today find to be very different are in fact descended from the same original root language, just as many people are descendants of one common ancestor in a family tree.

English, along with many of the languages of Europe, parts of Asia, and India are descendants of the same common ancestor language spoken perhaps 7,000 to 9,000 years ago: Proto-Indo-European (PIE). The discovery of these connections among languages, and the exploration of the historical changes in languages, cultures and peoples is one of the great detective stories of the 19th and 20th Centuries.

In describing the historical development of a language group we have recourse to various metaphors and "models."
One such metaphor is that of the family, by which we speak of the Proto-Indo-European parent language with its various descendants. Another metaphor is the botanical one, by which we speak of the Indo­-European stem with its several branches. These two metaphors are often combined in a family-tree model of language

Indo_European Lan Tree