In Bumgarner's _Mothering Your Nursing Toddler_: "Mothers have physical changes and hormonal shifts to trigger nurturing behavior, but fathers do not." No footnote to go with it. There have been numerous attempts to prove part (a) and success has been mixed to none. Unless you count mice mothers, but I'm pretty sure Bumgarner is sticking to humans here. To the extent there has been success at demonstrating (a), it has also been found in (b). Irritating.
Not precisely the same, but related: couvade has been found in other primates, and the weight gain is not all fat -- some of it is muscle.