The development of crop and animal raising as a food source among human communities to supplement hunting and gathering. This is thought to have first occurred among human groups in the Neolithic period (approximately 10 000 to 8 000 B.C.) It is worth noting that an agricultural revolution occurred in the new world independently of that in Europe or Asia. This allowed the civilizations of Mesoamerica to develop cities of at least 150,000 inhabitants long before urban areas of this size occurred in Europe.