To the south of the Philippines runs the so-called Wallace Line, a boundary between two biogeographic realms.

An excerpt from the article 24 facts about Philippines

The Wallace Line is a biogeographic barrier first drawn in 1863 by Alfred Russel Wallace, British naturalist, and explorer, with co-author Charles Darwin, of the theory of evolution by natural selection. This is a hypothetical line, a conventional boundary that separates Australasia (a geographic region including Australia, New Zealand, New Guinea, and a number of islands and archipelagos in the Oceania region) from mainland Southeast Asia. The line runs between the islands of Bali and Lombok, east of Java, continues between Borneo and Celebes, and passes south of the Philippines. 

Wallace was one of the first to note some characteristic differences in biota between these areas. The west of the line is dominated by oriental species, characteristic of Asia (tigers, Asian elephants, monkeys), while the east is dominated by Australasia (kangaroos, wombats, koalas, and birds of paradise).

The Wallace line is a key element of biogeography, helping to understand the distribution of species on Earth and the evolutionary processes that shape biodiversity on our planet.