One is the paper mulberry tree, native to Taiwan and Japan, which the Austronesian migrants took with them because they used its fibrous bark to make their cloth. A 2015 study of its genes supports the hypothesis that the species in Oceania are descended from those in Asia.
https://raskisimani.files.wordpress.com/2013/01/broussonetia-paper-mulberry.pdf
https://taiwantoday.tw/news.php?post=26541&unit=20%2C29%2C35&unitname=Taiwan-Review&postname=Austronesian-Roots&fbclid=IwAR0rEsePB0aR71MtPstwKguoqx-ZFsHNlw9r5JM0N0h1PbGW1kfIk849PF4
Another is linguistics. Professor Robert Blust https://en.wikipedia.org/wiki/Robert_Blust sorts the many languages of Taiwan into ten groups, only one of which (Malayo-Polynesian) developed into the Austronesian family of tongues.
https://en.wikipedia.org/wiki/Austronesian_languages#Blust_(1999)
https://en.wikipedia.org/wiki/Malayo-Polynesian_languages#Major_languages
A third is the study of human genes. A 2014 study of mitochondrial DNA from a c. 8,000-year-old skeleton unearthed on an island off the Chinese mainland links China to Taiwan and Austronesia.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3951936/
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| Figure 1: The Liangdao Man Skeleton (picture from here) |
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(Ibid., adapted from Figure 5) |
How did these humans cross over from the mainland? At its narrowest, the Taiwan Strait is about 130 kilometres (80 miles) between Fujian and Taiwan.
Things were different in the last Ice Age. The Strait is now some 100 metres deep, but:
'Pleistocene glaciations lowered [the] sea level 140m in the East China Sea 15,000 years ago, forming a land bridge between Taiwan and the mainland, with Palaeolithic artifacts on both sides. In the initial Holocene 10,000 years ago, melting ice raised the East China Sea 100m, quickly forming the Taiwan Strait.'
- from 'The Neolithic Taiwan Strait', by Kuang-chih Chang (1989)
https://web.archive.org/web/20120418153210/http://http-server.carleton.ca/~bgordon/Rice/papers/App.18ChangKC89.pdf
'Permafrost covered Asia as far south as Beijing,' says Wikipedia, so perhaps early humans were motivated to go further south, and some willing and able to walk over the exposed land between China and Taiwan.
https://en.wikipedia.org/wiki/Last_Glacial_Maximum#Asia
The end of the Ice Age saw rising sea levels: 'After the last ice age about 20,000 years ago, sea level initially rose due to the melting of the glaciers. That peaked around 4,000 to 5,000 years ago,' says geologist Chip Fletcher in this 2017 interview:
https://e360.yale.edu/features/as-seas-rise-tropical-pacific-islands-face-a-perfect-storm
One might think that this flooding was a spur to the development of boats, but although the earliest found by archaeological excavation date back 7,000 - 10,000 years, other evidence suggests that they existed tens of thousands of years earlier.
https://en.wikipedia.org/wiki/Boat#History
Indeed, recent finds in Central America suggest that homo sapiens may have arrived by sea 20,000 - 30,000 years ago and spread north and south from there, rather than coming though the Alaskan/Canadian ice corridor as previously thought:
http://polynesiantimes.blogspot.com/2020/07/origins-americas-first-colonised-in.html
Contrary to what one might assume, the post-glacial flooding was not uniform in all times and places. As the vast weight of ice was lifted from the land the continental plates started to shift about and rise up further from the Earth's mantle, like a ship being emptied of cargo. 'At the same time that Polynesians were undergoing their journeys of exploration and discovery, 1,000 to 3,000 years ago, sea level was falling and exposing coastal plains that then became habitable, where previously the sea was up against clay banks or cliffs,' says Fletcher. 'In the Pacific region [after c. 4,000-5,000 years ago], sea level started to fall until a few centuries ago. And now global warming is causing sea levels to rise again.'
https://e360.yale.edu/features/as-seas-rise-tropical-pacific-islands-face-a-perfect-storm
Although falling sea levels may have made it easier to land boats, 'around AD 1300 there was rapid global cooling, which was followed shortly by rapid sea-level fall – perhaps as much as 50-70 cm within 100 years in the Pacific [...]
'In almost every island group in the Pacific - from Solomon Islands and Fiji in the west to Rapa and Easter Island in the east – the first signs of collapse appear around AD 1300 with almost all hill forts beginning to be occupied around AD 1400. [...]
'Rapid sea-level fall along Pacific island coasts would have lowered coastal water tables, slowed water circulation within lagoons and killed (through exposure) the most productive parts of coral reefs. A food crisis would have resulted for coastal dwellers. Conflict followed. So people fled inland where they stayed, more or less, for several hundred years.'
https://theconversation.com/rise-and-fall-social-collapse-linked-to-sea-level-in-the-pacific-56268
So the interaction between geography, climate and human history is unexpectedly complex.
