The Zebra in the center is the leader. Older, a bit plumper but still tough enough to achieve the position and
remain in power.
The Zebra on the right of the leader is the "right hand man". It must constantly look over its shoulder, watching out for the younger Zebras who are continually
trying to work their way toward the center where the grass is greener and richer.
By the way, this is not about gender, it also works for "Good 'Ol Girls!"