In almost every part of the world where early man has lived he has made pictures by carving into natural rock surfaces . . . wherever they are found they always seem to lie just outside the area of easily explained phenomena. Almost nowhere in the world is there historic evidence relating to their origins. Even traditional histories and legends are generally lacking in useful clues. The present inhabitants of the various petroglyph areas throughout the world almost universally have no knowledge of who made them or why.
J. Halley Cox, Hawaiian Petroglyphs, Copyright 1970 by the Bishop Museum
Mr Halley goes on to talk about the similarities in these rock carving & why the imagery would remain constant across continents and over time: “They are always a very simple and basic symbol, the form of which is limited by the need for forming an immediate and permanent image of the self or a spirit, or the making of a functioning symbol. This need may have a variety of origins, but it is nearly universal with man and, at its simplest level, produces similar forms.”
Add to that the limitations of available tools and the likeness of stone surfaces producing similar results.