I agree that the talent for expressing yourself through drawing is genetic. It is in my family. My son was able to draw intricate pictures and make wonderful sculptures before he could read. I paint and my mother was a commercial artist. We never needed classes to teach us how, it was a natural ability. We just took them to perfect technique.
My father, sister and my daughter, on the other hand, can't draw to save their lives.
It was another poster who mentioned the possibility that the seemingly sudden appearance of cave art might be based on a genetic change. However, some families, like your own, are gifted, so there may be a genetic cause. Of course, children raised in an environment where art and music are going on, and where the implements, paint, brushes, clay, piano, stringed instruments are available, might be drawn to it even without a strong natural talent.
It's certainly a fascinating subject.