Though most of human existence has been sustained by hunting and gathering in band societies, many human societies transitioned to sedentary agriculture approximately 10,000 years ago, domesticating plants and animals, thus enabling the growth of civilization. These human societies subsequently expanded, establishing various forms of government and culture around the world, and unifying people within regions to form states and empires. The rapid advancement of scientific and medical understanding in the 19th and 20th centuries permitted the development of more efficient medical tools and healthier lifestyles, resulting in increased lifespans and causing the human population to rise exponentially. The global human population is about 7.8 billion in 2021.