Ken - I'm buying what you're selling; however, while I don't believe that there is a genetic predisposition to specifically be a softball or basketball etc. star, I do think that overall "athleticism" is genetically predisposed. As noted above, its the cultivation and development of that talent that determines the ultimate performance ceiling. All other things being relatively equal, hard work wins out.
Sorry if I wasn't clear. I completely agree with that. There's nothing that makes you a softball star, or basketball star, per se. But there are genetic advantages that allow you to perform better with less effort. Some kids are built for speed, some for power, some for endurance. Those are the genetic factors, and while they can be influenced you're going to have trouble teaching most big, strong, big-boned kids to be fast. NFL players seem to be an exception, but that's a whole other discussion.
Better natural hand-eye coordination will give you an early advantage. But it won't necessarily keep you the top infielder if others develop their skills and techniques.