Ericka Kammerer wrote:

However, other research has suggested that fathers who
are primary caregivers have similar physiologic responses. To
me, that undermines the notion that this plasticity and adaptivity
is purely female. A very viable alternate explanation is that
our society's concepts of mothering and fathering get in the
way of supporting the sort of infant-father bonding that can
trigger many of these same changes in the *father*. Perhaps
what this research is really finding is changes associated with
being the primary caregiver (which just happens to be the mother
in the overwhelming majority of cases) rather than changes
associated with motherhood in particular.

I'm not able to look this up right now, but I remember reading
something which suggested that there might also be a basic variable
which controls some of this, which is how *fast* a parent responds. I
think there was some reseach showing that men and women were both able
and willing to respond to an infant's needs, but that a typical man's
response was just slightly slower than a typical woman's response, so
that if a mother and father were around the infant together, the
chances were good that the woman would respond to many more of the
infant's signals just because she was a little more reactive. If this
goes on for long enough, the mother does get better at interacting with
the infant than the father, because she's done it a lot more times. So
you can take a very small difference which - who knows? - could even be
biolgically based but isn't very meaningful, and it prompts a whole
variety of changes which wind up looking like 'women are better at
taking care of babies'.

Beth