The history of human evolution has long been linked to increases in brain size, and now new research has discovered that hormones produced during pregnancy may play an unexpected role in this process. By studying the length of the thumb and ring finger (pointer and middle fingers), which indicate exposure to estrogen and testosterone during pregnancy, researchers found that higher estrogen levels were associated with larger head size in newborn boys.
The research, which offers a new perspective on human brain development, suggests that high levels of estrogen during pregnancy may result in larger brain size. This study was conducted by Professor John Manning of Swansea University, who has been studying finger ratios for years.
The length of the pointer and ring fingers is compared in the finger ratio (2D:4D), and this ratio reflects hormonal influences during the first trimester of pregnancy. The index finger is longer than the ring finger due to higher estrogen levels, making this ratio higher.
In this latest study, Professor Manning, together with researchers from Istanbul University’s Department of Anthropology, analyzed the head size and finger proportions of newborn babies. The study involved 225 newborns, including 100 boys and 125 girls.
The results of the study revealed that a higher 2D:4D ratio in boys, reflecting higher estrogen exposure in pregnancy, was associated with larger head size. However, no such association was found in girls.
Professor Manning explained the significance of this study and said, “This finding is important for human evolution, because increases in brain size are linked to skeletal feminization, known as the ‘estrogenized AP hypothesis’.”
Researchers say this study shows that estrogen during pregnancy plays a positive role in human brain development, although there are some biological problems associated with it.
This study also showed that finger ratio is related to brain size, which may prove important for future medical and developmental studies.
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