What forces determine the nature of an alphabet?

Primate language is all about vowel sounds and sorting out the world through 'song'.

Vowel sounds naturally associated with pleasure define the family grouping. Vowel sounds naturally associated with surprise, fear, or disgust define the external environment.
A set of vowels convey authority in the family setting, and also serve to declare authority outside of the family setting.
Counting is very rudimentary as a distinguishing factor although 'number sense' is as well developed in apes as it is in humans. Basically there is a number sense operating and active as a motivator but the basic number distinction is 'mine', 'yours', and a sense of size processed in terms of fear.

Come to think of it, this is basic humanity as well.