The smallest viable linguistic units in the Stone Age were biliteral roots constructed of two letters or segments of two inseprable letters.
Future needs to communicate a inc reased number of things and cases compelled the speakers to invent another set of biliteral roots formed by simply reversing the original biliteral root.
Development of Ancient Arabian until the advent of the Agricultural Era some 10,000-11,000 years ago depened primarily on compounds either of two identical biliteral roots or a pair of different biliteral roots.
During the Agriculutral Era a large number of words were needed to describe and identify the various activities of agriculutral. While the production of compounds continued, a new linguistic expansion involved adding a single letter before or after biliteral roots.
The new expansion known as triliterals became the essential form serving languages such as Ancient Arabic but they were used by other languages such as Gerhamite and Akkadian.
The slide in this post presents several linguistic clusters usually containing a primarly (invented first) biliteral root, a secondary (invented by reversing the two letters of the primary root) root, compounds and triliterals.