We appear to be talking up and down the family tree a lot more than across the tree.

From Horizontal and vertical family relationships, literarily by Philip N. Cohen. Cohen is a sociologist at University of Maryland.

Aunt and uncle yield to grandmother and grandfather.

In my Sociology of Family class, I ask the students to raise their hands if they experienced a substantial direct relationship with a great-grandparent. As all eight of my great-grandparents predeceased me, I am surprised that so many student raise their hands. (Maybe elite college students come from families with better health and healthcare, but still.)

Demographically speaking, the decline of fertility and the increase in survival to old ages has meant that we have fewer horizontal (intragenerational) relationships and more vertical (intergenerational) relationships. And these intergenerational relationships are also more intensive, lasting years and decades.

And so, for the question of the day: Does this shift from intragenerational to intergenerational show up in the giant Google book word database? As a one-day expert in ngramology, I can conclude: Mostly, yes.

The ratio of reference of Mother to sister; father to brother; grandfather to uncle; and grandmother to aunt, are all increasing. We appear to be talking up and down the family tree a lot more than across the tree.

An interesting fact. Its significance? To be determined. Perhaps none, but I suspect it is an indicator of some significance. Narrower families expose you to much less human behavioral variety. Literature can expose you to the tropes of the fretful, the cavalier, the cold, the effusive, the withdrawn, the hale-fellow-well met, the creepy uncle, the schoolmarm aunt, the morally loose cousin, the swot, and all the other rich variety of human behavior. But literature is an echo. Far more meaningful to see and experience it within the family.

I have wondered, occasionally, whether the seeming rise of left-right intolerance in recent decades might be functionally related to the narrowing of families. If you are not practiced at experiencing and accommodating behavioral variance within the family, how well prepared are you to do that in the real world of adulthood?

The psychological and economic safety also probably narrows for a member within the family tree. A wide tree gives you access to a wider range of personalities and circumstances. You are more likely to find a safe harbor when under stress if there are more people within the tree; people more likely to have both a familial commitment to you as well as a greater probability of finding someone with a temperamental empathy.

But that is just speculation. Cohen has some additional links worth looking at.