The Eridani are a mysterious alien species in the Pern universe. They were master geneticists, and had trained Kit Ping Yung. Little is known of them, other than that they take a very long-term view, and prefer to avoid altering ecosystems if at all possible. When they do make an alteration, a sacred obligation is produced to watch it and protect it for, not only the Eridani who performed the alteration, but her bloodline for thousands of generations. They prize harmony. A good change, they say, should be invisible. It should fit, seem like an obvious part of the ecosystem.