30-Second Overview: Pleistocene land bridges allowed continental species to migrate south, where they became trapped in Taiwan's mountains and evolved into endemic species;
The weevils of Lanyu tell Tadashio Kano that this small island, 80 km from Taiwan, is genetically part of the Philippines;
Across the same Bashi Channel, the ancestors of Austronesian peoples departed from Taiwan 5,000 years ago, spreading across the Pacific along the DNA of the paper mulberry.
Vertical Interweaving: Land Bridges and "Mountain Islands"
The natural history of Taiwan begins with the respiration of geological eras. The average depth of the Taiwan Strait is only about 60 meters; during multiple glacial periods of the Pleistocene, sea levels dropped by more than 120 meters, connecting Taiwan to the Eurasian continent and forming the "Taiwan Land Bridge."
Relics of the Ice Age: Relict Species
The land bridge served as a highway for species migration. As northern climates cooled, temperate species migrated south along the bridge. As interglacial periods brought warming temperatures, these species migrated to higher altitudes, turning Taiwan's mountains into "genetic refuges."
- Formosan Landlocked Salmon (Oncorhynchus masou formosanus): The most famous glacial relict. As the southern limit of the salmon family, they became "trapped" in the cold streams of the upper upper reaches of the Da'ya River due to rising temperatures, evolving into a landlocked species.
- Formosan Salamander (Hynobius formosanus): Belonging to the genus Hynobius, while the main body of these caudate amphibians is distributed across cold Siberia and Japan, the Formosan salamander is a rare living fossil left behind in Taiwan's mountains from the Ice Age.
These "mountain islands" not only preserve ancient genes but also accelerated the evolution of new species under long-term geographic isolation, explaining why Taiwan possesses an extremely high proportion of endemic species.
A Center of Ecological Convergence: The Northern Terminus of the Wallace Line
Taiwan does not merely connect to the north; it sits at the crossroads of East Asian zoogeographical regions. The coordinates of this crossroads are defined by an invisible line extending thousands of kilometers north from the equator—the Wallace Line.
In 1880, the founder of biogeography, Alfred Russel Wallace, turned his gaze toward Taiwan in his work The Malay Archipelago, calling it "terra incognita" (unknown land). He predicted that more than half of Taiwan's endemic bird species were phylogenetically derived from Himalayan and Malayan systems rather than neighboring China. This inference, which lacked almost any supporting data at the time, was gradually verified by 140 years of molecular phylogenetic research.
However, Wallace's line stopped in the waters south of Taiwan. Seventy years later, Japanese naturalist Tadashio Kano (鹿野忠 $\text{忠雄}$) collected a species of weevil from the Philippine system in the jungles of Lanyu, allowing this line to extend further north—cutting between the main island of Taiwan and Lanyu, forming what descendants call the "Kano Line."
Lanyu and Green Island thus become a unique buffer zone where the Philippine and East Asian systems converge, rather than a simple "either-or" boundary. For the full story of this line, Kano's fieldwork, and the significance of the "Out of Taiwan Hypothesis" in biogeography, see extended reading: [The Tropical Heritage of Lanyu: The Wallace Line and Tadashio Kano's Island Mystery].
The Expansion of Life: The Interplay of Anthropology and Biology
The most profound discovery of Taiwan's natural history is its confirmation as the starting point for the expansion of the Austronesian-speaking peoples. This argument was established not through a single discipline, but through the precise cross-verification of anthropology and biology.
The "Center" Theory in Linguistics and Archaeology
Linguists (such as Robert Blust) and archaeologists (such as Peter Bellwood) proposed the Out of Taiwan hypothesis.
- Linguistic Evidence: The Austronesian language family contains ten major branches, of which nine branches exist only in Taiwan (the ancient languages of Taiwan's indigenous peoples, collectively known as Proto-Austronesian). Only the final branch, "Malayo-Polynesian," covers the vast region from Madagascar to Easter Island. According to the "Center of Linguistic Diversity" theory, Taiwan is highly likely to be the origin of the Austronesian language family.
- Archaeological Evidence: The Tapenkeng Culture (大坌坑文化) from approximately 5,000 years ago exhibits cord-marked red pottery, agriculture (millet, rice), and sophisticated maritime navigation technology, which is believed to be the starting point for the Austronesian ancestors' maritime expansion.
Multi-faceted Evidence from Biological Genetics
To verify anthropological claims, scientists began tracing the DNA of "commensal species" that live in close symbiosis with humans.
- Paper Mulberry (Broussonetia papyrifera): A key study by researcher Chung Kuo-fang (鍾國芳) and his team at Academia Sinica. Paper mulberry is the raw material for making bark cloth and must be spread via human transport. Genetic data confirms that all paper mulberry on Pacific islands originated from southern Taiwanese populations.
- Pig (Sus scrofa): Through analysis of mitochondrial DNA in Asian domestic pigs, it was discovered that the genetic characteristics of pig populations in Oceania can be traced back to wild boar and indigenous domestic pig lineages in Taiwan, revealing the migratory path of pigs alongside Austronesian pioneers.
- Pacific Rat (Rattus exulans): This is a species of rat that is not a strong swimmer and must rely on human vessels for migration. Its genetic distribution pattern presents a "Taiwan—Philippines—Oceania" expansion route, perfectly consistent with anthropological predictions.
- Movement of Agricultural Crops: Core Austronesian crops such as taro, millet, and yam also exhibit genetic trajectories originating from Taiwan.
This dialogue between anthropology and biology reconstructs Taiwan's historical status as the mother port of Pacific civilization. Across the same Bashi Channel, species seeped north from the Philippines into Lanyu, while humans expanded south from Taiwan toward the Pacific. On both the axis of natural history and human history, Taiwan stands at that critical crossroads.
References
- Chung, K. F., et al. (2015). "A genetic signature of the Polynesian migration in the paper mulberry." PNAS.
- Bellwood, P. (2011). "Holocene populations, the spread of agriculture and language, and the rise of regionally distinct ethnic groups." In The Global Prehistory of Human Migration.
- Wang Chun-neng & Hsin Kuan-ting (2013). "Between the Ends of the Earth—Wallace's Biogeographical Affinities," Taiwan Natural History Quarterly, Vol. 120, No. 4.
- Tadashio Kano, Biogeographical Studies in Taiwan, translated by Lin Chao-chi.
- Chung Kuo-fang, "Viewing Austronesian Migration through Paper Mulberry," Scientific American (Chinese Edition).
- Lin Liang-kung, "Biogeographical Study of Mammals in Taiwan."