on low calorie
diets or who skip breakfast at the time of
conception are more likely to give
birth to girls than boys, British scientists said in
sex is associated
with the mother's diet, and higher energy intake is
linked to males.
This research may help to explain why in developed
countries, where many young women choose to have
diets, the proportion of boy born is falling.
There has been a small but consistent decline, of
about one per 1,000 births annually, in the
proportion of boys being born in industrialized
countries over the past 40 years.
In humans, going without breakfast may be
interpreted by the body as signaling low food
availability, since it depresses levels of blood
sugar. Although sex is genetically determined by
fathers, it is known that high levels of glucose
encourage the growth and development of male embryos
while inhibiting female ones, although the exact
mechanism is unclear.
George and colleagues studied 740 first-time
pregnant mothers in Britain and found 56 percent of
those in the group with the highest energy intake at
conception had sons, compared with 45 percent in the
lowest group. In evolutionary terms, this
correlation may make sense. Males' breeding
potential is strongly influenced by fitness, while
females breed more consistently.
a mother has plentiful resources then it can make
sense to invest in producing a son because he is
likely to produce more grandchildren than would a
daughter. However, in leaner times having a daughter
is a safer bet.
Some researchers have been sounding alarms for years
over the change in sex ratios in developed countries
and have in the past blamed pollutants and synthetic
chemicals such as those found in some pesticides
which disrupt human hormones.