Twins: a genealogical observation

[walkitout]

I just realized this last night but had to do a little checking to be absolutely sure.

I have four grandparents (you know, just like everyone else). None of my grandparents are themselves twins. All of my grandparents have twins-siblings.

All of them.

Is that weird? I still have to count the size of the group, but regardless, I think it is at least a little odd.

ETA: Okay, yup, that's odd. But I made an error. My maternal grandmother was half of a set of twins.

Paternal grandfather is one of 6, fraternal twins are two of them (girl and boy). Woman wound up in sanitarium for mental problem. Man died comparatively young for our family (in his 40s or 50s, IIRC, in a group of people commonly living to 80s).

Paternal grandmother is one of 3, not sure if they are fraternal or identical twins. Definitely both women.

Maternal grandfather is one of 14. Male twins.

Maternal grandmother is one of 7. Twins include her and a twin brother who died in 1920; I heard the story that he died of the Spanish Flu.

Total group size is 30, of whom 8 are twins. That sort of defies belief, actually.

Comments

[ethelmay.livejournal.com]

Well, you probably know all this, but highly fertile, long-lived women are more likely to have twins, and the twins they have are more likely to be healthy enough to survive. Higher parity and higher maternal age are both associated with twins, and to a slight extent so is height and weight (that is, taller, heavier women have more twins). This is all fraternal twins -- identical twins are essentially random (if there are any genetic or other factors predisposing one to identical twins, they aren't common enough to see across populations).

I don't think it's that odd that four families, three of them quite large, each happened to have *a* set of twins. After all, most families must have twins at some point. It's just that it was all in the same generation, among people who happened to marry one another, that makes it look like a trend.