Assume that Bob knocks up both Alice and Eve.

Alice has a son, Eve has a daughter.

Alice's son knocks up Eve's daughter.

Their kid will have two biological grandmothers, but only one biological grandfather.

Apparently, historically, this type of thing was quite common and could heavily skew family trees towards the female side of things.

That skews the tree shape, but the odds of each baby are still ~50/50 so the overall population numbers should be stable.

The overall population is roughly 50:50, but men are more likely to be the "final node" in the family tree.

Let's adjust the example above slightly to include Bob's friend Darren, who who never got laid because he spent his whole life watching pornography and playing video games.

Even in this case, despite the 50:50 ratio of males and females both across society as a whole and within each generation, the child has more male ancestors.

This will be the case for any sufficiently large population where males have more variance in reproductive success than females, and people (of either sex) reproduce with others who have a shared ancestor (the closer the ancestor, the greater the effect the variance has on the ratio of male to female ancestors).

Aussie was demonstrating how an individual could have more male ancestors than female ancestors. And his very simple example did in fact provide the 3:2 ratio that was previously mentioned.

I think I misunderstood the proposition. Sorry.

It doesn't because mating cousins is likely the effect of a skewed population,not the cause.

(im not a historian so this is speculation)

I imagine that early humans had divided roles, and roles assigned to males involved more danger. (bearing in mind that the state of medicine meant that relatively minor incidents by our standards could lead to infection and death in theirs.)

So populations start out 50/50,but skew badly once men age enough to take on dangerous work.

This leads to men having multiple partners and the scenario mentioned in the sibling comment.