We should study neurotransmitters of bonobo. Do Bonobo have really low serotonin?
Serotonin is considered to be related with discrimination in partner choice. And here we have a species which is the most indiscriminate (sexually), and also the happiest. Also high serotonine is usually correlated with happiness. So here we have the happiest group on the planet with a behavior that is usually correlated with hormones correlated with very low happiness.
I dare say we should study their hormonal system and neurotransmitter system really in depth.