In a letter by Charles Darwin to Asa Gray, introducing to him an abstract about what would Origin of Species, he talked about migration of different forms during the glacial epoch, and the reason why you could find European forms in the tropics. He then said: From mammalia and shallow sea, I believe Japan to have been joined to main land of China within no remote period ; and then the migration north and south before, during, and after the Glacial epoch would act on Japan, as on the corresponding latitude of China and the United States.

I wonder which sea he meant by "shallow sea", and why could this be reason to think that Japan and China were joined?

  • $\begingroup$ Hi. I'm glad you want to participate. However, your question is worded to imply that you doubt Darwin's statement. Please edit the question to explain why you doubt it. $\endgroup$
    – Spencer
    Jul 28, 2019 at 16:13
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    $\begingroup$ Reference: letter by Charles Darwin to Asa Gray on 11 August 1858. $\endgroup$ Jul 28, 2019 at 19:12
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    $\begingroup$ Likely the Korea Strait and the Strait of Tartary, both are shallow and narrow. Honestly this could be answered by just looking at a seafloor map of Japan. $\endgroup$
    – John
    Jul 29, 2019 at 14:46
  • $\begingroup$ Yes, during the last glacial maximum ~22k-~18k ocean levels where ~130m lower than they are now, so there were plenty of opportunities to simply walk into Japan and human appear to be in Japan since at least ~50,000years (sciencedirect.com/science/article/abs/pii/S1040618217300307). One can check ocean depths with an online chart viewer, like that at navionics.com, just as a hint. $\endgroup$
    – user18411
    Dec 6, 2019 at 15:26

1 Answer 1


At the northern and southern ends of the Sea of Japan, there are only short stretches of very shallow sea separating Japan from the mainland. During the Ice Age which ended 12,000 years ago, sea levels were much lower than they are today. It is probable that during the last Ice Age there were land bridges connecting Japan to the mainland at these two points.


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