One of the achievements is:
Heart Of Darkness -Become a chieftain of a zebra tribe. (How is this even possible?) - Have more then one zebra (sic)
I already have my first Zebra which I got when I built a ship. I only don't know how to get a second Zebra.
So how do I get the 2nd Zebra?
And do they add something more than just the achievement?