The bilateral symmetry of colored skin patterns of coral reef fish presents an impossible challenge to evolution.
The copper-banded butterflyfish shows bilateral symmetry of its vertical stripes. This is because one set of genetic instructions directs the creation of stripes for both halves of the body. The existence of a mid-line stripe between the two halves of the fish defies evolutionary explanations. One set of genes must direct the creation of one half of the composite mid-line stripe, so that the mirrored version perfectly matches the other stripes on the sides of its body.
In most animal species, such as the tiger and zebra, the joining of the two halves results in a "seam", indicating that coloration of each half of the body is directed by one set of genetic instructions.