Why Straight Lines?

Why should a visual recognition system expect straight lines? The arrangement of photoreceptors in the retina has no straight lines. Very little in nature that may be seen has straight lines. Primitive people do not build angular objects. Yet, I think straightness came from building things. What could be the first straight thing? Baskets? Arrows? Lines drawn in clay? Not even knife edges were straight. Maybe the horizon - out over the ocean. There is no survival value in building a recognition system within an animal upon a framework of straight lines. Except maybe for orientation to the horizon.
Why did Hubel and Wiesel concentrate on straight lines?
The things that are important to recognize are curved. In all directions. Food like berries, fruits, grasses and animals are all curved. The path upon which you walk. The trees over your head.
So can a recognition system be built upon collections of curves?