Evolution (Ancestors: The Humankind Odyssey)

It may have already resolved this issue, but I have not found. Anyways can someone explain how it works, I've taken three of evolution right now, somewhere in the 5.5 million years, but never understood. The first two times, I have evolved into a new phase, and thus lost tribe still remained, one monkey appeared randomly in the place, I thought well, maybe it should, but the third time I moved to a new stage has been spawned randomly in the place, but with the whole tribe except for children, so why can I th in the early times was done wrong or in the past? And every time they are looking for new monkeys hominids, and my looks unchanged.