Wegener first began to think about his continental drift hypothesis when he noticed a similarity in on different continents.

Coastlines

Explanation:

When we look at the continents as they currently exist in the world, we might notice that some coastlines that are on opposite ends of an ocean match each other. This observation is what led Wegener to first began to think about  the idea of continental drift. Continental drift refers to the slow movement of the continents on the surface of the Earth over time. This phenomenon is responsible for the current position of our continents.

brave new world, aldous huxley (1932)