Before anyone jaunts too far down the road of literal survivorship bias, I'd like to point out that it'd be incredibly premature—or perhaps way too late—to speculate much on the social side of things.

Elsewhere I've seen some people making hay about exactly whose-males were with whose-females, and want to point out that it's normal for genes to cause asymmetries.

In particular, consider the modern problem of RH incompatibility [0], where one pairing is more likely to end up with a child than an identical but gender-bent one.

[0] https://my.clevelandclinic.org/health/diseases/21053-rh-fact...

or even as simple as mitochondria...