International collaboration? (from This Week in Evolution)

The Royal Society just came out with a report on the internationalization (if that's a word) of science. China now produces the second-highest number of papers, but rates last in percent of papers involving international collaboration. Why so little collaboration? Three hypotheses:
1) the rest of the world doesn't realize all the great science they're doing in China, so is missing out on opportunities to collaborate with excellent researchers,
2) Chinese scientists are doing great work, but are reluctant to collaborate with ... College Major Book Notebook School