Early humanoids began to express symbolism in their built structures, as evidenced by the discovery of cave paintings and other forms of rock art. These early works of art suggest that early humans had developed a sense of symbolism and were capable of abstract thought and expression. The paintings often depict animals, humans, and other objects that may have held religious or cultural significance to the people who created them. The use of color and other artistic techniques also suggests that early humans had a sophisticated understanding of the natural world and were capable of creating complex works of art.