> Mac OS X on X86 is actually quite old, in the context that NEXTStep and OPENBSD
> it was based on
May I borrow your Reality Distortion Field?
The NeXT* used an M68040 cpu and was first released in 1988. DeRaadt didn't fork OpenBSD* until 1995.
NeXTSTEP* was "based on Unix", and specifically used the Mach (monolithic) kernel. Much has been said about the NeXTSTEP and Mac OS X userland; one study of the OS X RCS ID strings compiled into everything showed that – at that point in time – it was a mix of all the BSDs, and I'd wager that's still true.
No reason to make stuff up. It's all there in Wikipedia – among other places – for anyone to see.
*Note the correct capitalization. Please hand in your geek card at reception desk on your way out of the building.