Sorry I was unclear and yes, I indulged myself on the development because I think it is so neat.

To clarify the conclusion I am proposing that diet may be the key to social structure in both the baboon and gibbon case – high quality food -> non-hierarchical and pacifist – low quality food -> hierarchical and aggressive.

Since diet part of the experience of the animal is it nature or nurture or something in else? Does the diet trigger a genetic reaction or is it that with secure access to high quality food there is no reason for hierarchy and aggression?

And yes, it should be, “The pair sing together in the mornings and evenings to proclaim THEIR territories” not "there territories". Thank you.