The faithful get more parenting help
Saw this a couple of weeks ago: Faithful females key to evolution of bird societies. (It’s got lovely photos of a vermilion flycatcher, a white-fronted bee eater and, my favourite, a pair of pied babblers.) Among birds, apparently, those species in which the females are promiscuous are the same as those in which the aunts co-operate in raising the young. If the mother is sexually loyal to one mate, her sisters are more likely to help out with the kids.
The reason, they (Oxford’s zoology department and the Natural History Museum) think, is that when a female mates with only one male, all her offspring are full siblings – whereas the young of a female who has multiple partners will generally be half-siblings. And it makes evolutionary sense that nieces and nephews that are more closely related will be more conscientiously looked after.
The OU article I have linked to says this correlation has already been shown in various lower-order animals (if that term is still used), but now it’s been found true for vertebrates, possibly it holds for mammals too. Including primates… so, I have to wonder, including us?
Obviously morality, social pressure, and simply not knowing the kids are only half- and not full siblings (!) will all affect an aunt’s conscious decision on how often to babysit. But you never know.
As always, I like to think about cause and effect the other way round. I’d love to do a study to see if children who are more babysat (that term certainly isn’t used) grow up into adults who sleep around more. If you follow my promiscuous connection-making.