written by Alison Motluk
From New Scientist, 8 January 2000
Fatherly love
When new dads go gooey-eyed, blame their hormones
A pregnant woman is on a nine-month hormonal roller coaster--and it turns
out that the father of her child goes along for the ride. Researchers in
Canada have shown for the first time that expectant fathers' hormones also
fluctuate, and that the way they change mimics their partners' ups and
downs.
During pregnancy, levels of several hormones rise in an expectant
mother.These
include prolactin, which triggers lactation; the stress hormone cortisol,
which is known to be related to a mother's attraction to her child; and the
main female sex hormone, oestradiol.Immediately after the birth, the levels
crash. These hormonal changes are thought to be driven by the development
of the
baby in the womb.
Recently, however, studies in certain animals, including most birds, some
rodents and even a few primates, have shown that fathers are also
hormonally primed for the birth of their young (New Scientist, 12 December
1998, p 38). But until now no one knew whether the same was true for men.
Anne Storey of Memorial University in St John's, Newfoundland, and her
colleagues wanted to find out. They recruited 34 couples from an antenatal
class in a Newfoundland hospital and took blood samples at different times
during and after the pregnancies.
Twelve couples were sampled in the fourth or fifth month, eight in the last
month, nine three weeks after the birth, and eight between three and six
weeks after the birth. Most of the volunteers gave samples just once, but
two couples gave blood before and after the birth, and one couple donated
10 blood samples at different times during the pregnancy. The researchers
found that in fathers, levels of cortisol, prolactin and testosterone
changed significantly during their partners' pregnancies."The differences
for mums were much more drastic, but the patterns were similar," says
Storey. Testosterone dropped 33 per cent just after the baby's birth, and
lower levels of testosterone were associated with men becoming more
parental, they found. They will report their results in a future issue of
the journal Evolution and Human Behavior.
The team also asked fathers about changes that might signal a "sympathetic
pregnancy", such as fatigue, change of appetite and weight gain. Fathers
who reported these symptoms also had higher prolactin levels and a steeper
drop in testosterone than those who did not have these symptoms.
The researchers also studied short-term changes. After giving a blood
sample, volunteers listened to a six-minute tape of a newborn's cries and
watched a video about the trials of learning to breastfeed. Thirty minutes
later, their blood was sampled again. The researchers found that the men
experienced pronounced hormonal changes after exposure to the baby cues.
Like mothers, fathers' cortisol plummeted.
Storey speculates that a combination of behaviour and pheromones from a
pregnant woman somehow prompts the father to prepare for the birth of his
child. "There's something about the couple being together that sets the
stage," she says.
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