Teorya ng Tulay na Lupa o Wave of Migration Theory
According to the theory of H. Otley Beyer, a renowned archaeologist, the Philippines was once a part of the Asian continent because of land bridges. This geographical feature was common during the Pleistocene Period or the Ice Age some 1.8 million years ago. Waves of migrants from Mainland Asia made their way to the Philippines crossing these land bridges or Tulay na Lupa.
After the Glacial Period, the ice around the continent began to thaw, causing waters to rise and the oceans to form over the land bridges. The lands above sea level shaped the islands dotting the archipelago. This theory also explains the similarities of plants and animal species found in the country and in some parts of the Asian region.
The theory also identifies five land bridges that connected one area to another:
Palawan and Borneo
Philippines, Taiwan, and Asia
Borneo and Sulu-Mindanao
New Guinea-Mindanao (Jocano 1975)