I read the story back in the 90s, but it is probably older.
It is told from the point of view of a group of human xenobiologists in a "blind"/camp/lab studying the (apelike?) animals on an alien planet.
Contrary to the humans' previous experiences, individual animals become hostile and start attacking the scientists. Eventually one of the scientists also becomes violent.
It turns out an unknown third species - probably alien to this world - seeded this planet with weapons that when picked up use chemicals (and genetic manipulation?) to make the wielder hostile and hyper belligerent.
I believe the implication was that the weapons were used to fight a proxy war amongst native populations as a precursor to invasion. The invading aliens just seeded the planet with these weapons and waited for the dominant species to eliminate itself. The scientists just happened to get caught in the middle.