Like all vertebrates, snakes, mice and humans have in common a skeleton made of segments, the vertebrae. But a snake has between 200-400 ribs extending from all vertebrae, from the neck to the tail-end, whereas mice have only 13 pairs of ribs, and humans have 12 pairs, in both cases making up the ribcage. In a new study, researchers in Portugal reveal that, contrary to what was thought, making ribs is not the default state for vertebrates, but is actually an active process of balancing the activities of a remarkable class of genes -- the Hox genes.