"Today biologists believe that during the "Cambrian explosion," about half a billion years ago, nature experimented with a vast array of shapes and forms for tiny, emerging multicellular creatures. Some had spinal cords shaped like an X, Y, or Z. Some had radial symmetry like a starfish. By accident one had a spinal cord shaped like an I, with bilateral symmetry, and it was the ancestor of most mammals on Earth. So in principle the humanoid shape with bilateral symmetry, the same shape that Hollywood uses to depict aliens in space, does not necessarily have to apply to all intelligent life."