I wasn't aware of this and find it quite surprising, actually. Do you have a link to something that talks about this fact?
No direct data, but it's kind of a general principle. It's like asking, if a person is really strong, is it because they have naturally big muscles, or because they've done a lot of weight training? Well, it's the interaction of the two.
A person with a naturally slight build just won't be able to benefit much from weight training. A person with a robust build may be fairly weak with no training, but with good training they can get REALLY strong.
Put it another way, with little environmental opportunity, perhaps to the point of neglect, a person with natural talent and a person with little talent will look quite similar. It's when environmental opportunity is added to the mix that the differences between the two really show up.
As another example, consider someone who is naturally musically talented. With no musical training, they really won't look much different from someone with no musical talent. But with training, the talented person can go far and the untalented person can't.
