There seems to be quite a bit of anecdotal 'evidence' when I search. I think that fathers can be excellent primary caregivers -- because IMO anyone walking the walk and being in the primary position has the emotional ties that go with being that caregiver. If you want the position and do the parenting I can't see that (other than the nursing phase) it makes any difference. Plenty of men are simply fantastic parents.

This is a very interesting question but I would guess the confounding factors will be so immense that it will be very hard to get any reasonable results.

I think culture has a big part to play here. If a culture celebrates motherhood as the biggest achievement of a woman, and primarily sees it as her responsibility to raise a child, then yes, that culture will have mothers who are the better (if not only) primary caregiver. Fathers would tend to be the disciplinarian in the family and the secondary care giver of the baby. Barring that, I personally do not think there's general rule for who is the better care giver, biologically or psychologically speaking. Just like @Willow said.

@learner101 I don't think culture was part of the question though. In most places women are the primary caregivers for some pretty obvious reasons. That doesn't make it wrong for a father to be a primary caregiver or suggest that they can't be absolutely terrific at the job. I seriously doubt there is 'evidence' that proves one sex is better than another. One person over another -- certainly. Women have the advantage in this as it is often the way we are raised; while boys are encouraged elsewhere. My closest male friends have done a fantastic and loving job of parenting their three.

@Willow - "I don't think there is any evidence" is conjecture. There is evidence in the literature.

@anongoodnurse I think that (not including nursing) if men were equal in numbers to women as primary caregivers, the 'evidence' would be more believable. As long as women are paid less to do the same job and as long as society 'expects' certain functions from different sexes -- the evidence will be skewed to the subject.

If a woman can be as good as or even better than a man at medicine, that doesn't change that women are still fighting to be equals in that profession. Men can be fantastic parents. The stay at home Dad I know well certainly is. I think opportunity is far more of a factor in this. If men in general are less interested in being a primary caregiver, does that mean they are less capable? IMO, no.

@Willow - I think you're missing my point. There are studies on paternal primary caregiving. This is not asking for your (or my) opinion. It's asking for evidence. I'm saying, there are studies out there. I found two easily by searching in Scholar.

It's not a question asking for unsupported opinion.

If it did, I would close it for being POB.

As it is now, it's slightly unclear, because of associated remarks, what the OP is asking, but it's pretty clear that, while I think he's making assumptions, he wants evidence.

Not only are there studies of fathers as primary caregivers, there are also studies of paternal vs. maternal grandparental primary care givers! In other words, if the parents lose custody, which set of kin is most likely to do better as primaries (so far the literature states maternal grandparents tend to be more involved primaries.)

The world changes, fathers are more involved, and social scientists aren't blind to the fact.

Judges might be, and that's why specialists are called in to give testimony as to who would be the better custodian if it's not a 50-50 split.

So, I'll repeat (again): studies are requested as answers. You cannot state there are no studies out there if there are.

@Willow By the way, studies show pretty well that women are overall better doctors than men. :D

In nearly every measurable parameter, including lawsuits, health of their patients, patient satisfaction, missed diagnoses, etc., etc.