I'm surprised at how many people on this thread have said they don't think cognitive functions are inherited. How could they not be inherited? Where do we get them if they aren't dictated by the genes we get from our mothers and fathers.
Just because people can't decipher a pattern in their own immediate families doesn't mean that JCFs aren't a product of genetics. The way we inherit them could be much more complex than a simple A or B gene choice. Look at eye and hair color which is a result of multiple, competing genes. So it could be with the inheritance of cognitive functions.