Final answer:
The major proposed routes in the peopling of the Americas are the Bering Land Bridge theory and the coastal migration theory. Both theories suggest that humans migrated from Asia to the Americas, either by crossing a land bridge or following the Pacific coast. Currently, both theories are widely accepted.
Step-by-step explanation:
Scientific explanations of the origin of humans in the Americas focus on two major proposed routes: the Bering Land Bridge theory and the coastal migration theory. The Bering Land Bridge theory suggests that humans migrated from Asia to the Americas by crossing a land bridge that once connected northeast Siberia and Alaska. The coastal migration theory proposes that some peoples arrived in the Americas by following the coast of land across Asia, the Bering Land Bridge, and down the Pacific coast of North and South America.
Currently, both theories are widely accepted, and it is believed that humans first arrived in the Americas between 20,000 and 14,000 years ago. While the exact route of migration is still debated, evidence from genetic studies and archaeological sites support these two theories as the primary routes for the peopling of the Americas.