The Nadurni were an alien species.
In 1827 the Nadurni were in midst of a war with the Prokarian. Their mineral sources were depleted and their ability to mine other planets was comprimised. They thought that they could lose the war within the following months.
That was why three Nadurni came to the Amazon rainforest. There they experimented with animals and used a gene manipulator on them. They wanted to turn these animals into new warriors, so that they could win the war. Before that they had already experimented on themselves.
Later they also wanted to turn the Eleventh Doctor into a monster that would fight for them. They wanted to create a warrior who could cheat death. However the Doctor was saved by Oliver Blazington. The three Nadurni died in an explosion together with Oliver Blazington. (AUDIO: The Eye of the Jungle)
Years later the Eleventh Doctor visited the planet Nadurniss, a planet that had been under quarantine for centuries. The Nadurni had just started to move there again but got infected by a bacteria which caused them to die. Soon after this Amy Pond got infected. The Doctor travelled back in time to get a cure. There he found out the leader of the Nadurni had used his DNA to create the bacteria, which he wanted to use as a weapon. The leader was the first infected person, then other Nadurni got infected, the empire fell. The Narduni had to rebuild their society which made them less violent and less ruthless. (AUDIO: Sleepers in the Dust)