Perhaps not. But by the same logic there are no colors in nature, either.
Lines and colors are phenomena that manifest themselves in our our minds. At that level, lines are very real indeed. Perceiving boundaries is a fundamental aspect of our life as visual creatures. It is hard-wired into our perception.
“Lines are the bread and butter of our visual experience. They define trees, horizons, the edges of things we don’t want to bump into. Our visual system is designed to rapidly extract this meaningful information in order to make sense of the world. Consequently, the area in the visual cortex that first processes information coming in from the eyes is configured in a manner that reflects this preference for lines.”
Quote from Carl Schoonover in “Portraits of the Mind,” (2010)
Vanderpoel, The Human Figure, 1908
Norton, Freehand Perspective and Sketching
Lines and the Brain Series,