>Genetic differences are often overstated by comparing one extreme to another.

Upbringing differences are even more often overstated by comparing one extreme to another. In fact your entire comment was just that.

>Such limits are unknown until the given person puts many, many years of work into a particular goal (often at least five years.) That's because limits are not defined by where one starts, but where one plateaus for multiple years following some kind of improvement over the prior five, ten, fifteen years.

Genetics aren't some sort of magical limit that appear after pushing yourself hard at some pursuit for a decade. They're another variable, along with training, diet, etc. It's difficult to say what anybody's absolute limits are, but ball-park predictions are possible. And no microcephalic is ever going to be an excellent chess player, regardless of training.

In your example of sprinting, the best in the world was noticed and brought into the sport due to his talents. According to wikipedia, "Upon his entry to William Knibb Memorial High School, Bolt continued to focus on other sports, but his cricket coach noticed Bolt's speed on the pitch and urged him to try track and field events." And then, with less than a decade of serious training, he utterly demolished world records in three different events. Two other points that suggest a large genetic component in his success are that he had only recently started training for the 100 when he broke the world record, and that he was the fastest kid in his school while growing up, even before doing an track and field training.

>For example: it's possible that somebody on Hacker News has the kind of muscle fibers that speed runners dream of. However, that person would never know they are athletically gifted because they never got to the point where this ability mattered;

Muscle fibers are only the least of what goes into running talent. Paraplegics typically have a higher percentage of fast-twitch fibers than sprinters. That noted, the premise that someone on a relatively small site such as this might unknowingly have the same level of natural sprinting abilities as a freak of nature like Bolt is ridiculous. Only if one believed that all hereditary dormant was "dormant" until one trained for decades and that the bobcat's leaping power sprang from its upbringing would that be a sensible hypothesis.

There's a mountain of scientific data demonstrating natural differences in abilities between different people. In order to deny the existence of talent, you'd literally have to throw out the last fifty years of psychology, biology and related life sciences. Sadly, quite a few people are willing to do just that! The fact that there's an argument at all about nature and nurture both contributing greatly to life outcomes makes it clear that the influence of nature is severely underestimated. That Gladwell and others who lack any background in life sciences are getting so much play in the media on this topic only serve as further evidence. Here are some scientific findings on the subject of talent:

http://www.scientificamerican.com/article.cfm?id=a-gene-for-...

http://www.scienceblog.com/cms/musical-talent-genes-16460.ht...

http://www.thepsychologist.org.uk/blog/11/blogpost.cfm?threa...