Confirmation of Genetic Influence On Progeny Gender

There are genetic factors predisposing families to boys or girls. So that some families tend to have more girls or boys. Unknown if mothers or fathers. Age can magnify the effect.

There was another study maybe last year that says the effect is cross-generational, that the father inherit from their own mothers the immune factors to select for specific sex sperms. But this study apparently did not reference that. Because it only looked at nurses, and hence mothers.

But the fact that they can observe this gender trend says something. Because that means most of the observed mothers stayed with a single sexual partner long enough to have more than one child. Thus they were faithful enough to their spouses or partners. Which is not the observed outcome of infidelity studies.