There was an interesting Science Friday segment on this topic back in August 2016: http://www.sciencefriday.com/segments/a-hand-a-fin-a-gene/ http://www.scienc

There was an interesting Science Friday segment on this topic back in August 2016: http://www.sciencefriday.com/segments/a-hand-a-fin-a-gene/ http://www.sciencefriday.com/segments/a-hand-a-fin-a-gene/ A couple of comments made by the guests during the discussion (from memory): * there is a theory that humans/vertebrates actively repress regenerative abilities, * children under the age of about five have the ability to regrow cut-off fingertips, * the genetic instructions for growing a hand (or fin) consist of the thumb and little finger, and the rest get interpolated.