Our first four-legged land ancestor came out of the sea some 350 million years ago. Watching a lungfish, our closest living fish relative, crawl on its four pointed fins gives us an idea of what the first evolutionary steps on land probably looked like. However, the transitional path between fin structural elements in fish and limbs in tetrapods remains elusive. Both fish and land animals possess clusters of Hoxa and Hoxd genes, which are necessary for both fin and limb formation during embryonic development. Scientists compared the structure and behavior of these gene clusters in embryos from mice and zebrafish. The researchers discovered similar 3-dimensional DNA organization of the fish and mouse clusters, which indicates that the main mechanism used to pattern tetrapod limbs was already present in fish.