Scientific Method ANSWERS

  b.   Any properly controlled experiments allows  _ ONE _  Independent Variable(s) 

       But we have a definite problem.   Only you have your specific set of  G E N E S and only you
       have your specific  E N V I R O N M E N T A L  history.   That sounds like _TWO_
       Independent Variables, but it does not have to be that way if we decide to study  humans that
       are  I D E N T I C A L    T W I N S , since these siblings have the same  H E R E D I T Y. 

        Researchers have used twin studies in their long search for an answer to how much of each of
        us is determined by our  G E N E T I C S   and how much of us is determined by our
        E N V I R O N M E N T.

        This search is also known as the case for N A T U R E   versus  N U R T U R E, with the
        first blanked word representing our H E R E D I T Y   and the second blanked word
        representing our  E N V I R O N M E N T A L    variables. 

       The pendulum of time swings back and forth like that on a grandfather clock.  In some eras,
       researchers felt strongly that   H E R E D I T Y   was the dominant factor in determining your
       behaviors.  In others, researchers leaned more strongly to our social  E N V I R O N M E N T
       was the dominant factor in determining our behaviors.   Nobody can put an actual percentage
       on these two determiners of our behaviors.