There are biological reasons favoring dad as well. As the father of a toddler, I count physical strength as a huge asset. Example use case is carrying my sleeping infant holding with a single arm while the other hand unlocks the door.
> Example use case is carrying my sleeping infant holding with a single arm while the other hand unlocks the door
I think you are underestimating the strength (as well as form) women are born with, specifically for this reason. Most women I've seen carrying children on their hips with one arm behind their backs look much more comfortable than when a man does the same thing.
