Does an experiment always have a control group?

A control group is the group where the tested variable isn't present (ex. placebo in medical tests), but what if the experiment was whether brain dominance had an affect on I.Q. and once group was left brained and the other right. What would the control be then?|||In an experiment that simply compares A to B, each of the groups effectively serves as control for the other. Each is the standard against which the other is compared. You are comparing right-brained subjects to subjects who don't have that variable, and left-brained subjects to subjects who don't have that variable.