@PSX_Defector said:

But FreeBSD came out AFTER 4.1BSD, which is where the great schism started. Next started their work on Mach/Darwin a few years before FreeBSD came about. There is plenty borrowed from FreeBSD but it's still running kernels that are nothing like FreeBSD.

Yes, the ported the Mach kernel to the FreeBSD ecosystem. But the bulk of the code is from FreeBSD, not from Next/Mach. The OSX project started long after both FreeBSD and Next were established. That Next was older isn't really a big deal. OSX was much later. At the time, around 1999, they made a big deal that it was mostly FreeBSD with the Mach kernel swapped out for the old kernel.

Not totally unlike the Dragonfly project. Based on FreeBSD but taking the kernel in a different direction.