Piano players who do drills when they are children to improve dexterity in their left hands experience as a result.

I believe the answer is: brain changes that greatly improve dexterity

As we are conditioning ourselves to do something with a certain part of our body, our brain would eventually improve and adjust itself to make us able to do that thing better, even on automatic function. The same thing happen to soccer youths who are continuously trained to use both of their leg to make a maneuver ever since they're little.

"social stratification refers to the way people are ranked and ordered in society. in western societies, stratification is primarily seen and understood as a result of socioeconomic status, which produces a hierarchy in which access to resources, and possession of them, increases from the lower to the upper strata"

it gave them more rights