De-Evolution

The Human colonists must hunt for two children taken captive during a devastating storm by a member of what they thought was wildlife, but when they finally find the human children, they are being cared for by natives who had a thriving culture as little as 100 years ago, but who are now little more than cave dwellers. The humans have been here over a year, and now they start to realize that their memories are being, effected, much like the memories of the natives. If they don't figure out what is causing this de-evolution fast, they might be in the same situation as the natives. The human colonists are forced to follow a native animal that has taken 2 children hostage. When they finally catch us, they find the 'animal' is an intelligent native, whose people once had a thriving civilization... only 100 years ago. Then the human realize that something is affecting their memories, and if this keep up, they will soon be unable to complete building their colony. Can they figure out what is causing this drastic reduction in their intelligence and find a way to stop it before it's too late?