Genetic 'explanations' for human behavior

As I've mentioned in passing, I'm 59 years old. As with most older people, I can no longer focus properly on close work, such as when reading a book; no doubt most of this is due to age, but I expect that part of it is because I have spent most of my life staring at computer screens. Also, I understand that for most people, this inability to focus properly generally becomes a problem at about age 40. In my case, I began noticing it at around age 52 or 53 ... and, to this day, cheap (i.e. $1.50) reading glasses, at the lowest level (1.25) take care of the problem for me.

On the other hand, my mother needed glasses before age 30 and my father not long after. My twin sisters needed glasses from childhood. Our brother is somewhere in between (but closer to my condition that to the girls').

So, two human beings, both of whom had faulty vision from a relatively young age, produced four children (with three genetic profiles), two of whom (having a single genetic profile) had worse vision that either of the parents (*), and two of whom had better vision that either of them, and at least one of those has vision that is at least one or two standard deviations better than average.

So, given how useless looking at peoples' genes would be in telling one physical facts about their children, such as what the children's vision would be like, how does it even begin to make sense to "explain" human behavior in terms of genes, especially when one ignores culture to do so?



(*) My sisters had three children each, and only one of the six needed glasses as a child.