The human brain has grown throughout evolution, and researchers have long sought to understand why.
A new peer-reviewed study from Swansea University, published in Early Human Development, indicates that estrogen during the fetal stage may have played a role.
The researchers link their findings to the theory that larger human brains evolved alongside more feminized skeletal traits.
At the same time, they point out that these biological changes may have come at a cost, including an increased risk of certain health problems in men.
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Study among newborns
The study is based on measurements of 225 newborns, including 100 boys and 125 girls. The research team also included anthropologists from Istanbul University.
The infants’ head circumference was measured and compared with the ratio between the lengths of the index and ring fingers.
Head circumference is often used as an indirect measure of brain size.
The results showed an association among boys. A higher 2D:4D ratio was linked to a larger head circumference. The same association was not found among the girls.
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What is the 2D:4D ratio?
The 2D:4D ratio describes the relationship between the lengths of the index and ring fingers.
In research, it is used as an indirect marker of the balance between estrogen and testosterone during the first trimester of pregnancy.
A relatively longer index finger is associated with higher exposure to estrogen before birth.
According to the researchers, the findings may contribute to understanding how prenatal hormones could have influenced the development of the human brain.
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Sources: Science Daily, and Early Human Development.
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