Scientists examine why men even exist

[Donald Ian Rankin]

7. Another question is why are there so many.

It's a straightforward biological theorem that you want to invest an equal amount of energy into your sons and your daughters, because every grandchild will have exactly one father and one mother, so on average they'll pass on the same number of genes (although this is only true on average - there's some fascinating research suggesting that in some species higher-status females have more sons than daughters, and lower-status females the reverse).

But in many species (although less so among monogamous ones like humans) the variance in number of children is significantly higher for a son than a daughter, and so is the competition, so it's not obvious to me why a winning strategy isn't to have fewer, larger sons and more, smaller daughters, so that your sons will outcompete your neighbour's and father a higher proportion of the next generation but one. But I don't know of any species that do this.