This diagram is only a very simplify unix history. There are a lot more unix like systems than those listed in this chart, maybe 10 times more ! Some years ago, every electronic company has it's own unix system. For example, my company was selling an unix, derivated from another one, and those two are not in this chart because there are too small. So this diagram is only the upper part of an iceberg, with a penguin on it ;-).
Unix History [1]
It's simplified. It's also 9 feet in length! Three meters for those of you who are Imperially challenged. It makes a neat poster, although I'm not sure where I can hang a 9 foot poster.