72 Science & technology The Economist June 4th 2022
Testosterone and family lifeLike father,
like son?
M
ost males in the animal kingdom do
little parenting. Their strategy is sim-
ple: inseminate as many females as possi-
ble and hope for the best. Sometimes,
though, parental investment by a male
pays off. Songbird chicks are usually tend-
ed by both mother and father. Wolf packs
see alpha males and females collaborate to
raise the cubs. And in human beings, too,
the children’s father hangs around to lend
a hand in bringing up the kids.
Sometimes.
Understanding why some men settle
down to form families with the mothers of
their children, and others don’t, is normal-
ly seen as the prerogative of social science.
But biology has a role, too. And work just
published in the Proceedings of the National
Academy of Sciences, by Lee Gettler of the
University of Notre Dame, in Indiana,
clarifies how part of that biological mecha-
nism, testosterone, operates.
Previous studies suggest that high lev-
els of testosterone, the principal male hor-
mone, are bad for family life. Fathers with
lower testosterone levels provide more
child care and are better partners to the
children’s mothers. Indeed, fatherhood is
often associated with a drop in testoster-
one levels. Conversely, high-testosterone
males are less likely to stick around.
Dr Gettler has shown something fur-
ther. This is that a man’s adult testosterone
level seems correlated with whether his fa-
ther was present during his teenage years.
His data come from a survey begun in Cebu
City, in the Philippines, in 1983. This mon-
itored the health and nutrition of 966 men
enrolled as babies. It also collected exten-
sive information on whether the fathers of
these men were around and providing pa-
rental care in the households in which they
were brought up. It further documented
whether participants got married, had
children and, if they did, whether they par-
ticipated in child care. Crucially, it also
measured their testosterone levels at the
ages of 21, 26 and 30.
Overall, Dr Gettler and his colleagues
found that on becoming fathers, men had
lower testosterone levels if their own fa-
thers had lived with them and been in-
volved in their care during their teenage
years. Specifically, if that had happened,
testosterone levels in their saliva were 16%
below those of men whose fathers had not
stuck around to help raise them.
This difference has two possible expla-nations. One is that it is directly genetic,
with high-testosterone fathers (those least
likely to stick around) begetting high-tes-
tosterone sons. In this case the correlation
with paternal absence would be a coinci-
dence. The other is that teenage experience
actually modulates testosterone levels.
This explanation, which Dr Gettler favours,
could lead to a vicious circle of high-tes-
tosterone men abandoning their sons,
who thus become high-testosterone in
their turn.
Testosterone levels are not, Dr Gettler
found, completely deterministic in the
matter of parental care. Some of those in
the survey whose fathers were absent dur-
ing their adolescence, and who ended up
with high levels of the hormone, did never-
theless became nurturing parents. But
they are indicative.
Why this pattern should pertain is an
unanswered question. But a zoologist
looking at these data might be tempted to
see in them an example of developmental
plasticity, in which the same genes pro-
duce different, but appropriate, outcomes
in different circumstances.
If nurturing young carries a cost in re-
productive opportunities foregone else-
where (which it presumably does), then it
would not have been favoured by evolution
in times of uncertainty—the sorts of times
that lead to early death. A dead man cannot
care for his children, and dead children
cannot be cared for. Better, evolutionarily
speaking, to spread your genes far and
wide while you can. Since the absence of a
father could, in turn, mark such uncertain
times, for that absence to trigger a high-
testosterone developmental pathway en-
couraging this would make sense, even if it
is not appropriate to the modern world.
That is speculation. But whatever the
truth, Dr Gettler’s discovery surely throws
a useful light on the problem of fatherless
families, and how to try to end it. Sons of absent fathers have more of the
main male hormoneAerodynamicsO for the wings
of an albatross
W
hile chatting to a customer in the
family bicycle shop in Dayton, Ohio,
Wilbur Wright was idly twisting a piece of
cardboard that had once contained an in-
ner tube, when he came up with an idea.
The “semi-rigid” way in which the card-
board could be deformed yet still retain its
stiffness might, he considered, provide an
answer to a little problem he was working
on with his brother Orville: how to design awing for a heavier-than-air flying machine.
The Wright brothers knew, from orni-
thological observations, that if a wing on
one side of a bird’s body meets the oncom-
ing flow of air at a greater angle than the
opposite wing does, then that wing will
rise. An aircraft wing which could be made
to twist like this would help a pilot bank
and turn. Using mechanical gears and le-
vers to rotate an entire fully-rigid wing to
do that would make the plane too heavy. A
semi-rigid wing, however, could be warped
into different angles using a lightweight
series of wires and pulleys. Which is how,
on December 17th 1903, the brothers
achieved the first controlled and sustained
flight of a powered aircraft.
The Wright brothers called their system
wing-warping. But it did not last. Within a
few years, aviators began adopting a more
reliable form of control that fitted hinged
ailerons and flaps to the trailing edges of
wings, and in 1915 Orville (Wilbur having
died three years earlier) conceded, and fol-
lowed suit. But, in a slightly different
guise, wing-warping is now back. And not
only that. In their efforts to make wings
more efficient, which saves fuel, aerospace
engineers are also looking for inspiration
from birds’ wings in another way, by bor-
rowing a trick from the most accomplished
long-range flyer of them all, the albatross.
Airbus, a giant European producer of
passenger jets, recently completed a series
of tests on new forms of wing control using
a model in a wind tunnel at Filton, near
Bristol, in south-western Britain. As a re-
sult, the company is now fitting these sys-
tems to a specially built wing that will, as
an experiment, be used to replace one of
those on a Cessna Citation business jet.
This aircraft will then test the new designs
in real flying conditions.
One feature of the eXtra Performance
Wing, as it is called, is that instead of hav-Borrowing tricks from birds may result
in smoother flightsNot just for the birds...