Genes for life on land evolved earlier in fish.

Almost 700 years ago, Jacob van Maerlant, a Dutch naturalist, envisioned a fish that was all set for life on land: It had sprouted arms to hoist itself ashore. New genetic studies make his fantasy look remarkably prescient. Together, the studies suggest that in terms of genes, the aquatic precursors of tetrapods—four-limbed land animals—were as well-prepared as the Dutch fantasy fish. They were pre-equipped with genes for making limbs, lungs that could efficiently breathe air, and nervous systems tuned to the challenges of life on land. By sequencing the genomes of a lungfish and several early evolving fish, researchers discovered the origins of tetrapods were something waiting to happen. Another study uncovered a hidden genetic pathway that caused zebrafish to grow forearmlike bones in their fins, demonstrating how a small mutation could unleash hidden pathways for limb development.