There are approximately 6,000-7,000 languages spoken in the world today, with 3,000 estimated to become extinct. Mandarin Chinese is the most widely spoken with over 1 billion speakers. The major language families include Indo-European, Afro-Asiatic, Austronesian, and Sino-Tibetan. Writing systems developed independently in various cultures and include alphabets, abjads, syllabaries, and logographic scripts. The advent of writing coincided with the rise of agriculture and the need to record property and transactions. Linguistic diversity is threatened by a growing rate of language endangerment and extinction, with cultural and historical knowledge lost when languages disappear.