Scholars believe that the Americas remained uninhabited by humans until a drop in the level of the Pacific Ocean uncovered a land bridge from Asia where the Aleutian Islands of Alaska are presently located. Commencing approximately 50,000 years ago, several Asian peoples of different origins and ethnic backgrounds migrated in successive waves across the Bering land bridge. Subsequently, the sea levels rose and covered the land, leading the migrants to develop culture and technologies wholly separate from those of the so-called Old World of Asia, Europe, and Africa. By 13,000 b.c. these migratory huntergatherers had moved through the Darién jungles of Panama and established encampments on the Peruvian coast and in Chile. Separate peoples crossed the Andes, slowly occupying the Amazon Basin, from which they moved north and settled the Caribbean Islands. Farther south, the migrants fanned out thinly over the Pampas and Patagonia of present-day Argentina. In the time of the pharaohs of ancient Egypt, approximately 1,000 b.c., the Mesoamericans of lowland Mexico were developing agriculture around the cultivation of maize or corn. The fisher peoples of coastal Peru adopted the cultivation of maize, while the highland Andeans of Peru subsequently perfected the cultivation of several varieties of potato. These hearty Andean peoples also nurtured the only domestic livestock known in the Americas, the llamas and alpacas. Some of these Andean developments reached the peoples of Chile and northwest Argentina. Indigenous influences from the area of modern-day Brazil, in the meantime, had spread into the area of modern-day Paraguay. There the Guaraní cultivated cassava (also known as yuca or manioc) as their basic food product. The rest of the indigenous peoples of the lower Paraná River basin, the Pampas, and Patagonia remained hunters of game and gatherers of fruits and berries.