Another moment of genius from the Viz letters page...and it's a fair point
 

First few were barter.

Grog give dead lizard for "once around the world". Then be back as soon as kill next lizard.

Yes...Grog not truly cognizant of world being flat or round...just heard "talk" underneath rock overhang on lower cave.

First men invented credit.

Hi,
 
Grok!
 
No grok!
 
Who grok?
 
Baba grok!
 
Gagagoogoo grok.
 
I doubt, that it was intended as a profession. According to Greek and some Sumerian myths before the time of Moses, it was a sort of Bed and Breakfast ... literally!
 
The rest is simple religious brouhaha for the sake of population control!

slartabartfast
First men invented credit.

Be interested to know how the ladies picked up the interest in that discussion! You know ... the interest on the principal owed!