Writing vs. Drawing

Today I've come up with a new theory that drawing ability and writing ability are mutually exclusive, and that a person who excels in one area will be poor in the other. This is based my experiences of today when I was practising drawing. This morning (among other things) I drew several figures in a variety of poses. The drawing was fairly accurate and came easily. Later I read a few chapters of Germinal, and soon after drew again. My drawing in this second session however was not very good and I found it very difficult despite the conditions and difficulty of the poses being about the same. I have noticed before that sometimes my drawing comes easily and sometimes doesn't, perhaps this influence is controllable. The most notable mental activity between the two drawing sessions was one of reading and it might be that the imagination or perhaps language parts of the brain were sucking away drawing abilities. This made me think of whether any great artists or draughtsman were great writers and vice versa and I could think of hardly any. There certainly are some famous musician painters but few writing painters (mostly poets, or children's book authors who illustrated their own work, none exceptional in either field). If I were an academic I would probably conduct an experiment. In the mean time however I will try to avoid thinking in words when I need drawing skills, just in case.