Edgar Zwilling and John Saunders observed chicken embryos by cutting and moving various tissues to discover that two small pieces of tissue controlled the development of the bone pattern of the chick inside the limbs

Edgar Zwilling and John Saunders observed chicken embryos by cutting and moving various tissues to discover that two small pieces of tissue controlled the development of the bone pattern of the chick inside the limbs. Those specific pieces of tissues being removed changed how its arms developed. This suggests that evolution of fish fins transforming into limbs did not involve the origin of new DNA and was instead a matter genes working in new ways to form limbs with toes and fingers. The hedgehog genes were found in fruit flies. Scientists then started to search for the hedgehog gene in other creatures like chickens, mice, and fish. Eventually, the chicken hedgehog gene was discovered and renamed the Sonic hedgehog gene. This gene was found in the ZPA of the chicken in the wing bud and when active, develops pinky and thumb digits. This gene is significant to building upper arms, forearms, wrists and digits.