Researchers from the universities of Cambridge and Oxford suggest that hormones produced by the placenta influenced brain development. These substances, such as testosterone and estrogen, play a role in cognition and social interactions from fetal life onward.
Mini-brains, created in the lab from stem cells, have allowed researchers to observe the impact of these hormones. Testosterone appears to increase brain size, while estrogen enhances connections between neurons. These discoveries open new perspectives on our evolution.
The human ability to form large social groups may also stem from these hormonal mechanisms. Unlike other primates, humans exhibit less pronounced sexual differences, which may promote social cohesion. The placenta, by regulating these hormones, may have played a central role.
Previous studies show that estrogen levels are higher in pregnant humans than in other primates. This particularity could explain some of the physical and behavioral characteristics unique to our species.
The enzyme aromatase, more prevalent in humans, converts testosterone into estrogen. This conversion may have reduced male competition and increased female fertility, thus facilitating the emergence of societies.
This hypothesis places pregnancy at the heart of human evolution. The placenta, by modulating sex hormones, may have not only enabled the development of a larger and more connected brain but also the emergence of unique cognitive and social traits.
How do placental hormones influence brain development?
Hormones produced by the placenta, such as testosterone and estrogen, have a direct impact on brain formation. They act on neuron proliferation and the creation of synapses, the connections between these cells.
These substances cross the placental barrier and reach the fetus, where they modulate brain growth. High levels of estrogen, for example, promote better neural connectivity, essential for complex cognitive functions.
Imbalances in these hormones can have consequences for neurological development. This could explain some variations in social and cognitive abilities observed in individuals.
This discovery highlights the importance of the intrauterine environment in brain formation. It also opens avenues for understanding certain neurodevelopmental conditions, such as autism.
Why do humans form larger societies than other primates?
The size of human social groups far exceeds that observed in our closest primate relatives. This particularity may be linked to hormonal adaptations that occurred during our evolution.
Placental hormones, by reducing sexual differences, may have decreased competition between males. This reduction in conflict could have allowed for better cooperation within groups.
Simultaneously, increased estrogen levels may have improved female fertility. A larger and more stable population could thus have been maintained, favoring the expansion of human societies.
These hormonal changes, combined with a more developed brain, may have created the ideal conditions for the emergence of advanced cultures. It is this unique alchemy that distinguishes humanity from the rest of the animal kingdom.