Karma is the stuff you CAN take with you when you die in FaoD. But what stuff is that?
So you have the option of applying for rebirth in a specific lineage. In the afterlife menu you can see active generations of your own offspring and possibly other than ages that you somehow have access to?
The point is you apply to be reborn in a certain lineage. the more specific your request along you may have to wait because they will have to be a fertile parent or an egg or just dating fetus or something waiting for you that matches your request. On the other hand if you don't want to wait you can just put in an open application and be reborn in the very next generation as soon as any birth is available.