 News
18th June 2008
Feisty women more likely to have boysFeisty
women are more likely to give birth to boys than girls, according to scientists.
High levels of testosterone in the womb - apparently evident in more aggressive
women - provide a much better environment for the sperm coded to produce boys,
they claim. But fiery females whose hearts are set on a daughter shouldn't
throw out those pretty pink baby dresses just yet. So far the correlation
has been proved only in tests on animals. The scientists who carried out
the research, however, expect the same outcome will be seen in humans.
And those girls with an aggressive streak won't be the only ones expecting boys.
Testosterone levels rise in women under stress so those feeling anxious
could also be in line for sons, according to the scientists. At the most
basic level, it is the type of sperm which decides whether a child is a boy or
a girl. If the sperm which fertilises the egg contains an X chromosome,
a girl will be born; but if it is a Y chromosome, a boy is the result. However
the environment within a woman's womb affects the likelihood of different types
of sperm making it to the egg first. This study appears to show that -
at least in cows - a higher than average amount of testosterone in the womb makes
it easier for Y-bearing sperm than X sperm. Testosterone levels in women
are linked to traits of maternal dominance and aggression. To prove the
link, scientists in New Zealand extracted the follicles from cow ovaries, which
contain eggs. The follicles were tested for levels of testosterone, and
then the eggs were fertilised in the lab. The sexes of the resulting embryos
were ascertained and then compared with testosterone levels in the follicles from
which they came. Team leader Dr Valerie Grant, of Auckland University,
said: 'Results showed that follicular testosterone levels were significantly higher
for subsequently male embryos.' She said the fact that testosterone levels
rose in women after experiencing chronic stress could mean that they were more
likely to have boys after a nerve-racking experience. Scientists had previously
thought sex selection was a matter of chance based simply on which sperm reached
the egg first. But this could not explain how some animals had managed
to change the ratio of male and females born as they had evolved. Where
to next? | 
