Are you as ignorant as me?

I am constantly astounded by my lack of knowledge. This is something I learned recently.

Everyone is familiar with holly trees as a symbol of this time of year. If you look at holly trees in the fall you will notice that some are convered with fruit and others have absolutely none. This is completely natural and both types of tree are perfectly healthy. What accounts for the difference?

I suspect that this is something that people 100 years ago knew perfectly well. Are we losing touch with nature? Or maybe just me.