30-second overview: Ice Age land bridges allowed mainland species southward, where they were sealed within Taiwan's high mountains and evolved into endemic species;
the lycid beetles of Orchid Island told Tadao Kano that this small island 80 kilometers from Taiwan belongs, in its bones, to the Philippines;
yet across that same Bashi Channel, five thousand years ago the ancestors of the Austronesian peoples set out from Taiwan, spreading across the Pacific along with the DNA of the paper mulberry.
Vertical Interweaving: Land Bridges and "Sky Islands"
The starting point of Taiwan's natural history lies in the breathing of geological time. The Taiwan Strait averages only about 60 meters in depth. During the 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 became a highway for species migration. As northern climates cooled, temperate species moved south along the bridge. When interglacial warming returned, these species shifted to higher elevations, turning Taiwan's high mountains into "genetic refugia."
- Formosan landlocked salmon (Oncorhynchus masou formosanus): The most famous glacial relict. As the southernmost member of the salmon family, they were "trapped" in the cold headwater streams of the Dajia River by rising temperatures, evolving into a landlocked form.
- Formosan salamander (Hynobius formosanus): Belonging to the genus Hynobius, whose main distribution lies in cold Siberia and Japan, the Formosan salamander is a rare living fossil left behind on Taiwan's high mountains during the Ice Age.
These "sky islands" not only preserved ancient genes but, through prolonged geographic isolation, accelerated the evolution of new species—explaining why Taiwan harbors an exceptionally high proportion of endemic species.
An Ecological Melting Pot: The Northern Terminus of Wallace's Line
Taiwan does not only link to the north; it sits at the crossroads of East Asian biogeographic realms. The coordinates of this crossroads are defined by an invisible line stretching thousands of kilometers northward from the equator—Wallace's Line.
In 1880, in his work Island Life, the founder of biogeography Alfred Russel Wallace turned his gaze to Taiwan, calling it a "beautiful unknown land" (terra incognita). He predicted that more than half of Taiwan's endemic bird species would trace their affinities to Himalayan and Malay systems rather than to neighboring mainland China. This inference, made at a time when almost no data existed to support it, has been progressively confirmed over the following 140 years by molecular phylogenetic studies.
Yet Wallace's line stopped at the waters south of Taiwan. Seventy years later, the Japanese naturalist Tadao Kano collected Philippine-system lycid beetles in the forests of Orchid Island, extending the line further north—cutting between Taiwan proper and Orchid Island to form what later scholars called "Kano's Line."
Orchid Island and Green Island thus became a special buffer zone where the Philippine and East Asian systems converge, rather than a binary either/or defined by a single line. For the full story of this line, Tadao Kano's fieldwork, and the biogeographic significance of the "Out of Taiwan" hypothesis, see the extended reading: [Orchid Island's Tropical Origins: Wallace's Line and Tadao Kano's Island Puzzle].
The Spread of Life: Where Anthropology and Biology Illuminate Each Other
The most world-shaking discovery in Taiwan's island natural history is its identification as the starting point of the dispersal of Austronesian-speaking peoples. This thesis was not established by a single discipline alone but through the precise corroboration of anthropology and biology.
The "Center Theory" of Anthropology and Linguistics
Linguists (such as Robert Blust) and archaeologists (such as Peter Bellwood) proposed the Out of Taiwan hypothesis.
- Linguistic evidence: The Austronesian language family comprises ten major branches, of which nine are found exclusively in Taiwan (the indigenous ancestral languages, collectively termed Proto-Austronesian), while the tenth branch—the Malayo-Polynesian languages—covers the vast region from Madagascar to Easter Island. According to the "center of linguistic diversity" principle, Taiwan is very likely the homeland of the Austronesian language family.
- Archaeological evidence: The Tapenkeng Culture, dating to approximately 5,000 years ago, exhibits cord-marked red pottery, agriculture (millet, rice), and sophisticated maritime navigation technology—regarded as the starting point from which Austronesian ancestors began their oceanic dispersal.
Multiple Corroborations from Biological Genetics
To validate the anthropological thesis, scientists began tracking the DNA of "commensal species"—organisms that live in close association with humans.
- Paper mulberry (Broussonetia papyrifera): A landmark study by the team of Chung Kuo-fang at Academia Sinica. Paper mulberry is the raw material for bark cloth and must be spread by human carriers. Genetic data confirmed that all paper mulberry across the Pacific islands derives from southern Taiwan populations.
- Pigs (Sus scrofa): Analysis of mitochondrial DNA in Asian domestic pigs revealed that the genetic signature of Oceania's domestic pig populations can be traced back to Taiwanese wild boar and native domestic pig lineages, indicating that pigs traveled alongside Austronesian pioneers.
- Polynesian rat (Rattus exulans): A poor swimmer that must rely on human vessels for dispersal. Its genetic distribution map reveals a "Taiwan–Philippines–Oceania" dispersal route, perfectly consistent with anthropological predictions.
- Movement of agricultural crops: Core Austronesian crops such as taro, millet, and yam also show, through genetics, life trajectories originating from Taiwan.
This dialogue between anthropology and biology has reconstructed Taiwan's historical status as the mother port of Pacific civilization. Across that same Bashi Channel, biological species filtered northward from the Philippines into Orchid Island, while humans dispersed southward from Taiwan into the Pacific. Taiwan, on both the axis of life history and the axis of human history, stands at that pivotal 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 Jun-neng and Xin Guan-ting (2013). "Between the Ends of the Earth: Wallace's Biogeographic Romance," Taiwan Natural Science Quarterly, No. 120, Vol. 32, No. 4.
- Tadao Kano, Studies in the Biogeography of Taiwan, translated by Chao Chao-ching.
- Chung Kuo-fang, "Tracing Austronesian Migration Through the Paper Mulberry," Scientific American (Taiwan edition).
- Lin Liang-gong, "Biogeographic Research on Mammals of Taiwan."