Why do many scientists support the land bridge theory of migration? check all of the boxes that apply. 1. there is a land bridge connecting asia and north america today. 2. a land bridge connected asia and north america thousands of years ago. 3. a land bridge would have allowed the first migrants to spread rapidly across north america. 4. crossing the land bridge would have been simple for the first migrants. 5. people might have crossed a land bridge while hunting animals.