Tobacco smoking is the inhalation of smoke from burned dried or cured leaves of the tobacco plant, most often in the form of a cigarette. People may smoke casually for pleasure, habitually to satisfy an addiction to the nicotine present in tobacco and to the act of smoking, or in response to social pressure. In some societies, people smoke for ritualisticpurposes. According to the WHO about one-third of the world's male population smokes tobacco.Tobacco use by Native Americans throughout North and South America dates back to 2000 BC.