Round up some male monkeys. Put them in a group together, and give them plenty of time to sort out where they stand with each other - affiliative friendships, grudges and dislikes. Give them enough time to form a dominance hierarchy, a linear ranking system of numbers 1 through 5. This is the hierarchical sort of system where number 3, for example, can pass his day throwing around his weight with numbers 4 and 5, ripping off their monkey chow, forcing them to relinquish the best spots to sit in, but, at the same time, remembering to deal with numbers 1 and 2 shit-eating obsequiousness. Hierarchy in place, it's time to do your experiment. Take the third-ranking monkey and give him some testosterone. Inject a ton of it into him...give him enough testosterone to grow antlers and a beard on every neuron in the brain. And, no surprise, when you check the behavioral data, it turns out that he will probably be participating in more aggressive interactions than before.
So even though small fluctuations in the levels of the hormone don't seem to matter much, testosterone still causes aggression. But that would be wrong. Check out number 3 more closely. Is he now raining aggressive terror on any and all in the group, frothing in an androgenic glaze of indiscriminate violence. Not at all. He's still judiciously kowtowing to numbers 1 and 2, but has simply become a total bastard to numbers 4 and 5.