I read somewhere that the original Dravidian number system was base-eight.
Indeed the names for our numbers reflect this.
One through seven have unique roots.
Eight is എട്ടു which comes from എണ്, which actually means 'number'. (Compare with എണ്ണുക, എണ്ണം)
Nine is ഒമ്പത് which came from തൊമ്പത് = തൊള് + പത് , "almost ten". Compare with 90 തൊണ്ണൂറ് , 900 തൊള്ളായിരം. (Aside: This used to be a bit confusing when I was a little kid.)
Ten is പത്ത് which came from പന്തി which is a തത്ഭവം of പങ്ക്തി, meaning row. Probably derived from saying "there is a row of things".
Now, we all know that our current base-ten system was a result of humans having ten fingers. So how can a base-eight system evolve "naturally"?
My explanation is that early Dravidians might have used their thumbs to touch other fingers when they counted. This leaves the eight fingers to do the actual counting leading to the development of the octal system.