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In the book, astronauts in a shuttle are in orbit around a planet or moon to monitor it in some sort of exploration. However, while they are in orbit, an alien species actually evolves from cellular level to space flight at a very greatly increased speed of evolution. I remember the planet having very high gravity, the aliens being almost mound shaped and mostly flat, and them telling the humans at the end that they wouldn't share what they had learned. That's all I can remember. Any ideas?