Khaberni - Scientists at Swansea University in the UK have discovered a relationship between the length of newborns' fingers and the size of their brains.
This supports the hypothesis known as the "estrogen-influenced monkey", which suggests that hormone levels in the womb play a pivotal role in the development of human intelligence.
According to the journal Early Human Development, human development is closely linked to an increase in brain size, and the new study shows that this process depends on the level of estrogen in the womb. The key to this connection lies in a simple anatomical detail, namely the length of the fingers.
Professor John Manning, an expert in the study of finger length ratio (index to ring finger 2D:4D), pointed out that the impact of hormones on fetal growth extends over a long period. A higher length of the index finger compared to the ring finger (high 2D:4D ratio) indicates a higher level of estrogen relative to testosterone in the first trimester of pregnancy.
The scientists measured the fingers and head circumference of 225 newborns (100 males and 125 females), and found that a high prenatal estrogen level in males directly correlates with a larger head size and thus brain size, while this correlation was not observed in females.
The professor confirms that this discovery supports the hypothesis of the "estrogen-influenced monkey," which assumes that brain enlargement coincided with the feminization of the skeletal structure, although this evolutionary progress comes with some costs.
He explained, "A higher finger index in men is often associated with an increased risk of heart disease, lower sperm count, and a predisposition to schizophrenia."
Scientists believe that the evolutionary need for a larger brain has led to a decline in physical fitness in males and an increased prevalence of certain diseases, while the larger brain compensates for these shortcomings and ensures the survival of the species through intelligence.
