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A groundbreaking hypothesis from researchers at the Universities of Cambridge and Oxford suggests that the placenta and the hormones it produces during pregnancy may have played a pivotal role in the evolution of the human brain and the unique behavioral traits that distinguish our species.
The study, published in Evolutionary Anthropology, argues that prenatal sex steroid hormones—such as testosterone and estrogen—not only influence the developing brain and behavior but may also be a driving force behind the cognitive and social abilities that have enabled humans to form large, complex societies. Small variations in these hormones in the womb can predict rates of social and cognitive learning in infants and even the likelihood of conditions such as autism, prompting scientists to consider their broader evolutionary significance.
Dr. Alex Tsompanidis, senior researcher at the Autism Research Centre at the University of Cambridge and lead author of the study, emphasized that the human brain does not develop in isolation. “Our hypothesis puts pregnancy at the heart of our story as a species. Adaptations in the placenta and the way it produces sex steroid hormones may have been crucial for our brain’s evolution, and for the emergence of the cognitive and social traits that make us human,” he said.
Recent research using “mini-brains”—clusters of human neuronal cells grown in the lab—has revealed that testosterone can increase brain size, while estrogens can enhance connectivity between neurons. The placenta acts as a critical link between the mother’s and baby’s endocrine systems, regulating both the duration of pregnancy and the supply of nutrients and hormones necessary for brain development.
Notably, human pregnancies exhibit higher levels of estrogen compared to other primates, which may contribute to the development of our uniquely large and interconnected brains. The researchers also suggest that the placenta’s increased ability to convert testosterone to estrogens—via an enzyme called aromatase—may have reduced competition between males and improved fertility in females, facilitating the formation of larger, more cohesive social groups.
Professor Simon Baron-Cohen, Director of the Autism Research Centre and joint senior author, highlighted the long-term study of prenatal sex steroids and their impact on neurodiversity. “This new hypothesis takes this further in arguing that these hormones may have also shaped the evolution of the human brain,” he said.
Disclaimer:
This news article is based on a recent scientific hypothesis and does not constitute medical advice. The views and findings presented are those of the researchers and may not be universally accepted. Further research is needed to confirm these findings and understand their full implications. Always consult a qualified healthcare professional for information regarding pregnancy, brain development, or neurodevelopmental conditions.
