In the domain of learning and children psychology they studied the behaviour of identical twins that are either separated or living together, and found differences that can't be explained. These studies seem to support the fact that each one has also some unique characteristics, not explicable through genes alone. Still, since NO TWO ENVIROMENTS ARE EVER THE SAME, it is very difficult to go on with an argument about an immaterial substance; at the same time, these same studies aren't the best support you can get for the materialism theory.