The argument that having five girls for every boy would be better for the species is new to me.
I've seen it in a lot of places; it works better for species where male parental investment is minimal (which isn't as true for humans). Even then, the "good of the species" math and the "good for my line" math point in different directions.
or: Why Everything Is Terrible, An Overview.1
It sounds like a theory which explains too much. But it's not a theory, hardly even an explanation, more a pattern that manifests itself once you start trying to seriously answer rhetorical questions about the state of the world. From many perspectives, it's obvious to the point of being mundane, practically tautological, but sometimes such obvious facts are worth pointing out regardless.
The idea is this: The subset of participants which rises to prominence in any area does so because its members have traits helpful to becoming prominent, not necessarily because they have traits which are desirable. Thus, without ongoing and concerted effort, a great many arenas end up dominated by players employing strategies which are bad for everyone.
This comes up again and again: