What's the primary theory behind tracks in the stone around the world? Even if they are ancient roads, why there are no traces from the horses or other animals that should be in the middle?
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I agree with @T.E.D., this may be a natural sciences question & it may be better suited to SE Earth Science. Many of the tracks look like erosion. This can be the result of a weakness in the rock due to a crack or other discontinuity experiencing water erosion.
Other causes could be the breakdown of the geology because of the weight bearing down on wheels, particularly steel rimmed wagon wheels. If the wheels continually follow within the same tracks over a prolonged period ruts will develop.
As to why animal tracks wouldn't be preserved, the weight of the animals would have been significantly less than the weight of the loads on the wheels of the wagons.