Updated June 8th, 2019.
The original Mac keyboard didn’t have function keys. It also didn’t have cursor keys. It also didn’t have Page Up and Page Down keys, a Control key, or an Escape key. Why? Well, the IBM PC had all of those things, and the Mac was positioned as the anti-PC. Plus, the Mac was heavily mouse-oriented, which made the “missing” keys less important.
You should have heard it clack. It really made a racket.