On page 242 of The Moral Animal, Robert Wright states that
In vervet monkey societies, dominant males have more of the neurotransmitter serotonin than do their subordinates. And one study found that in college fraternities, officers, on average, have more serotonin than do their less powerful fraternity brothers.
However, on page 82 of a different book, Scattered: How ADD Originates and What You Can Do About It, Gabor Maté states that
In troops of monkeys, the dominant, most successfully aggressive males have been found to have less serotonin than others. This would seem to prove that low serotonin levels cause aggression. However, the serotonin levels drop only after these males achieve dominant status. So while the relative lack of serotonin may help to maintain the dominant male's aggressive capacities, it could not have caused them.
It seems that Wright (a journalist) is making the complete opposite interpretation of the primate research that Maté (a physician) is, and there doesn't seem to be any subtlety in the context that alleviates the seemingly glaring contradiction, so I'm assuming that one of these two simply misunderstood the research. Who is correct?
(to be clear, both of these people are citing research that others have done, not making claims based on their own research)