1. The Bering Strait is a narrow passage of the Pacific Ocean that separates Asia from North America.

At its narrowest, the strait is 82 km across.

It is generally accepted that when sea levels were lower in the past, a ‘land-bridge’ in the strait was exposed, allowing animals to migrate from Asia to North America, and vice versa. When sea levels rose, the land-bridge disappeared.

Explain how the emergence and disappearance of a land-bridge could have fuelled speciation.