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Girls with fraternal male twins may earn less and be less likely to thrive in society, new research suggests.
Researchers in Norway and at Northwestern University posit that exposure to their brother's testosterone in the womb may damage the female twin, resulting in poorer cognitive functioning and fertility.
Studies - Humans - Testosterone - Exposure - Way
Though studies on humans vary, it may be that this testosterone exposure alters the way females develop, leading to more masculine traits that could explain the lower probability that these girls find partners and marry later in life.
Understanding these outcomes is more important now than ever, the researchers say, as IVF has let to a near two-fold increase in the number of twins born annually.
Disparities - Man - Woman - US
The disparities between any man and any woman in the US (and abroad) are clear and undeniable.
Men make more but die earlier.
Women - College - Degree - Access
Women are now more likely to get a college degree but have poorer access to healthcare.
The list goes on.
Twins - Share - Influence - Womb - Twins
But twins share a rare influence on one another, beginning in the womb - and it's becoming increasingly clear that even between twins, the female may be at a disadvantage.
Certain patterns and trends in male-female pairs have long been observed, including some worrying possible disadvantages for the girl half of the pair.
Number - Studies - Womb - Twins - Sexes
A number of studies have tried to examine how sharing a womb might affect twins, especially if they are of different sexes.
Though unproven, the 'twin testosterone-transfer hypothesis' suggests that the roots these divergent paths might be traced back to male hormones that a female twin is exposed to when developing alongside a boy.
Fetuses - Sac - Nutrients - Antibodies - Hormones
Fetuses develop in an amniotic sac swirling with nutrients, antibodies and hormones and get their blood supply from their mother - and twin fetuses share this fluid and blood supply with one another, too.
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