The picture below shows what happened in the experiment. The dotted line marks where scientists cut off the limb of a salamander. It would be like having another whole arm extending off of your hand. Scientists have also applied retinoids to the limb buds of tadpoles as they begin to develop into frogs. Retinoids and Human Deformity Certain kinds of retinoids have been shown to cause severe birth defects in people.
Some medications contain retinoids.
Unfortunately, when pregnant women used this medication, their babies were born with severe deformities. Notice that the pregnant women did not develop any deformities. The retinoids only affected their babies that were still developing. Some scientists have argued that we should be concerned that retinoids may be ending up in the environment because we know they can cause deformities in people. I used the image from Stan Sessions web page on Methoprene.