Fish, mice and likely all modern-day vertebrates share genetic elements first used to develop the unpaired dorsal fin in ancient fish. They later copied these elements to produce paired appendages, like pelvic and pectoral fins, arms and legs.
Fish, mice and likely all modern-day vertebrates share genetic elements first used to develop the unpaired dorsal fin in ancient fish. They later copied these elements to produce paired appendages, like pelvic and pectoral fins, arms and legs.