Environment does not exert any appreciable influence either.

Both decimal and vigesimal numeration are found indifferently in warm and in cold countries; in fruitful and in barren lands; in maritime and in inland regions; and among highly civilized or deeply degraded peoples.
Whether or not the principal number base of any tribe is to be 20 seems to depend entirely upon a single consideration; are the fingers alone used as an aid to counting, or are both fingers and toes used?
If only the fingers are employed, the resulting scale must become decimal if sufficiently extended.

If use is made of the toes in addition to the fingers, the outcome must inevitably be a vigesimal system.

Subordinate to either one of these the quinary may and often does appear.

It is never the principal base in any extended system.
To the statement just made respecting the origin of vigesimal counting, exception may, of course, be taken.