I highly doubt that the roughhousing/social flexibility connection is a cause/effect relationship. I'd be more inclined to interpret that data as the personality which at a young age leans toward roughhousing, also inclines an older person toward social flexibility. My surmising is based on anecdotal evidence, however.
For example, our son (now 14) liked to roughhouse as a young boy, but not even close to the level of the neighbor boys' enjoyment of roughhousing (they were the same age). He would stand back and watch, would dart in-and-out quickly, but would not engage in the activity nearly as much. It wasn't because his parents didn't roughhouse with him (we did), nor was it because he is an only child (some of the other boys he watched were only children). He just didn't like it as much. Now, if you look at him compared with those same neighbor boys, they are far more socially flexible than he is. The boy in the neighborhood who was even less inclined to roughhousing is even less socially flexible.
I take that to be a personality issue that causes both effects, not that roughhousing causes social flexibility. If that makes sense.
