“(A note for older readers: More time separates us today from the debut of the first iPod than separated the first iPod from the debut of the first Macintosh computer.)“
Wow.
Wow.
You could take NeXT back to Thompson & Ritchie. NeXTStep as ur-Aqua is also a fair argument, but again, not occurring on mainline Mac generally. By that argument Classic Mac might be traced to the Alto and MOAD.
according to wikipedia classic MacOS was partially based on Lisa OS, whereas OS X is nothing more or less than a full port of NeXTStep with a slight visual update. i have used both. they are the same UI. the difference is cosmetic. it's the same code too. i believe the kernel has changed more than the UI layer.
the question is not the spiritual ancestors but how old the code is that is still in use today. and i belive that if we look we'll find some Objective-C code in OS X today that goes all the way back to the first versions of NeXTStep.