Female vervet monkeys manipulate males into fighting battles by lavishing attention on brave soldiers while giving noncombatants the cold shoulder:
After a skirmish with a rival gang, usually over food, females would groom males that had fought hardest, while snapping at those that abstained.
When the next battle came along, both those singled out for attention and those aggressively shunned would participate more vigorously in combat, according to a study published in the journal Proceedings of the Royal Society B.
That reminds me of what Phil Sheridan said: “A soldier who won’t fornicate won’t fight.” Or words to that effect.