YDNA will show you the large family group of Clark(e)s back to before surnames. It might even show that your forebear wasn't a Clark, but another surname -- called Non-paternity events. YDNA won't tell you the name of your gr,gr,gr-grandfather or whether you descend from his son "George, John or William." It will only get you into a ball park family group IF other relatives have participated in this study. This is what our study is attempting to do...