Eric Lévénez has produced pdf files with charts displaying the very complex history of Unix/Linux. They are available in different formats. For me, the plotter variant was the best to view in Okular with 125% as you can easily scroll through the time axis. A history of Windows is also available on his site.
That's some serious geeky stuff Thanks! That Eric guy looks like a uber-major hacker ... he can probably melt your brain talking about VT100 or suchlike. Mrk
If you want more than a diagram, you have to read Eric S. Raymond's "The Art Of Unix Programming." In chapter 2, he gives a nice overview of Unix history. http://catb.org/~esr/writings/taoup/html/historychapter.html