Characteristics

At the beginning of Weitz the differences in characteristics is addressed. This is particularly looked at through family portraits. I thought that this was interesting because so often people look for what is similar they don't look for what may be unique to an individual. While there can often be similarities, it is the differences that make something what it is. People aren't the same so art shouldn't be either. Do you agree with Weitz when he says that are evolves?