Assumes Correlation and Causation, ignores Social and Economic situations of the twins groups, doesn't account for the fact that identical twins tend to share (being geared towards) more experiences due to being perceived almost as a single "being", ignores cultural differences in upbringing of different-gender twins, doesn't account for indirect training (i.e. strategy, memorization, sequential steps etc. are parts of a Chess game), doesn't account for perception of time (Time passes slowly when we don't like what we're doing) and completely ignores training "quality" (Playing chess against newbies is useless as practice, playing against masters is enlightening).<p>It's ALSO not your "fault" that you do not excel at something. Your experiences ever since you were a baby shaped you, your tastes and pretty much determined your whole life.<p>Still, there is no talent, ask any great programmer, musician, illustrator or whatever, every single one of them will say he/she was shitty, but loved it, so kept doing it. This doesn't completely discards the possibility of genetic disposition to liking something, but undeniably everyone starts on even ground.<p>Obviously, being complex areas they are affected by many indirect skills, and the more something is loved, the safer it is to assume the indirect skills involved are also loved or at least liked, indirect skills matter. Clearly fiddling with computers and watching movies that involve technology is not programming, but will make you better at it.<p>In the end, the best explanation so far is that your tastes are the defining factor. And yes, it can be argued that tastes are genetic, but currently there's not nearly enough data to debunk the standing theory, we need more studies and we need better studies, taking all variables into account and actually monitoring the subjects throughout their lives.<p>Maybe in 50 years we'll find out where our tastes come from. Not that it actually matters since it's out of our control anyways.