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The morning before

Question: What is the evolutionary advantage of morning sickness? Why are so
many pregnant women incapacitated and unable to eat sensibly for the first three
months of their pregnancy and how can this possibly help the developing embryo?
Do any other animals get morning sickness?

Answer: The quick answer to this question is that statistically morning
sickness reduces the likelihood of miscarriage, pre-term birth, low birthweight
and perinatal death. More interesting is the question of how this advantage is
conferred. No one really knows, although several theories have been
advanced.

The traditional hypothesis is that nausea and vomiting make pregnant women
avoid foodstuffs containing chemicals likely to harm the fetus during the
critical period of organ formation. There is a variety of evidence to support
this: symptoms peak when embryonic organogenesis is most susceptible to chemical
disruption, between 6 and 18 weeks into pregnancy; women who experience morning
sickness are less likely to miscarry than women who do not; women who vomit
suffer fewer miscarriages than those who experience nausea alone; and many
pregnant women have aversions to alcoholic and caffeinated drinks and
strong-tasting vegetables, especially during the first trimester.

However, because it appears that the greatest aversions are to meat, fish,
poultry and eggs, the theory now goes that the purpose is to reduce exposure to
potential food-borne pathogens. This may be because the immune system is
weakened during this period of pregnancy.

An interesting alternative hypothesis put forward recently is that starving
the mother during the first trimester causes a corresponding increase in the
size of the placenta. This ensures better nutrition for the fetus for the rest
of the pregnancy, reducing the risk of miscarriage.

I understand that this has been known to sheep farmers for some time.
Apparently, many of them ensure that their ewes are mated while feeding on poor
pasture, where they remain for the first half of the pregnancy before being
moved to better pasture for the remainder. The result is larger lambs,
presumably because the starvation during early pregnancy results in a larger
placenta.

However, I know of one study of this in humans which failed to find any
significant link between vomiting in early pregnancy and higher birthweight. On
the other hand, vomiting in late pregnancy was found to lead to significantly
reduced birthweight.

Dr Thomas R. Lee

By e-mail, no address supplied

Answer: Margie Profet has written extensively on morning sickness as an
evolutionary adaptation. She argues that food aversions and vomiting in early
pregnancy are a way of ensuring that embryos are protected from toxins that
could harm them while the limbs and major organ systems are forming.

There is, however, a cost associated with pregnancy sickness: the loss of
important nutrients. It is presumably for this reason that morning sickness
stops once the embryo has developed into a fetus and is less vulnerable to
toxins. One recent study found that morning sickness is likely to harm the fetus
if the mother already suffers from poor nutrition. But for well-nourished women,
the adaptive view of morning sickness implies that they should be wary of
treatments that eliminate symptoms.

More research is needed into morning sickness in other animals, but most
mammals and other creatures already display an innate or learned aversion to
potentially harmful foods. Some mammals show physiological changes during
pregnancy that heighten sensitivity to toxins. But Profet points out that
morning sickness is most likely to evolve in creatures that experiment, eating a
wide variety of foods.

Women can experience dangerous amounts of vomiting during pregnancy, and
should never hesitate to seek medical advice. But in general they should look
upon morning sickness not as an affliction but as a mechanism designed to
protect the embryo.

David Hardman

Department of Psychology

London Guildhall University

Boxing clever

Question: How do box kites fly?

Answer: Box kites, like nearly all kites, fly in a stalled condition. They
are designed to be flown in strong winds. The bridle and string hold the kite at
an angle to the wind, which forces air downwards to generate lift while the air
passing over the upper surfaces breaks away in turbulence. The stalled condition
generates far less lift that the smooth flow over an aeroplane’s wing but is
sufficient to lift the relatively light structure of a kite.

The side panels channel airflow to prevent turbulence breaking away from
alternate edges of the kite. Without the panels, the kite is unstable and liable
to crash. In a classic diamond kite, the tail damps out the wiggles caused by
this turbulence.

The side panels of a box kite resist any turning forces by blowing the kite
body back into line if it yaws—twists about its vertical axis. The gap
between the two box sections helps to smooth the airflow, and the low ratio of
the kite’s length to its width reduces the effect of turbulence on the kite’s
orientation, helping it to stay upright and not nosedive. Box kites are not the
sort of kite to try stunts with but are certainly the best choice for a winter
gale.

Peter Lane

Peterborough, Cambridgeshire

This week’s questions

Bee lines 1: Children at my school are always asking me how bees make honey.
Can anyone help me explain?

Sally Bunker

By e-mail, no address supplied

Bee lines 2: Instead of foraging randomly for nectar, bees tend to stay with
the same plant species during a collecting session. The plants benefit from this
by being pollinated—but what’s in it for the bees?

Jim Sullivan

Warrington, Cheshire

Kalashnikov surfing: If I fire a gun at one of the buttons on my TV remote
control, will the remote have enough time to send a signal to change channel
before it is destroyed?

Dadayev Tohir

Tashkent, Uzbekistan

We all know how frustrating it is to be lying on the couch watching TV and
discover the remote control has been left over the other side of the room. But
we recommend readers do not resort to shooting the remote without adequate
supervision from qualified military personnel—Ed