The human brain is one of the most complex objects in the Universe, and this complexity may be caused by a surge of hormones released by the placenta during pregnancy, reports New Scientist, writes UNN.
Details
Although, as stated, many ideas have been proposed to explain the evolution of the human brain, it remains one of the greatest scientific mysteries. One explanation, known as the social brain hypothesis, suggests that our large brains evolved to manage complex social relationships. It argues that managing the dynamics of large groups requires a certain degree of cognitive ability, pushing social species to develop larger brains. For example, other highly social animals, such as dolphins and elephants, also have relatively large brains. But the biological mechanism underlying this connection remains unclear.
Now, Alex Tzompandidis from Cambridge University and his colleagues say that placental sex hormones may be the answer. During pregnancy, the placenta - a temporary organ that acts as an intermediary between the fetus and the mother - produces hormones that are crucial for fetal development. These include sex hormones such as estrogens and androgens.
"I know it seems like a leap - to think about human evolution and then end up at the placenta," says Tzompandidis. "But the reason is that we study the fluctuations and changes in the levels of these hormones in the womb and see that they predict things like language development and social development."
New research also shows that these hormones affect the developing brain. For example, a 2022 study showed that administering androgens, such as testosterone, to brain organoids - simplified, miniature versions of the brain created from human stem cells - during a critical developmental period increases the number of cells in the cortex, a brain region crucial for memory, learning, and thinking. Other studies of brain organoids have shown that estrogens are important for forming and stabilizing connections between neurons.
There is also some limited evidence that humans are exposed to higher levels of these hormones during pregnancy than non-human primates. A 1983 study showed that gorillas and chimpanzees have four to five times less estrogen in their urine during pregnancy than humans. The placenta also has greater activity in genes that produce aromatase - an enzyme that converts androgens to estrogens - in humans compared to macaques.
"These hormones have become very important for brain development, and if we compare them to other primates and other species, there is probably evidence that these hormones are very high in humans [during pregnancy]," says Tzompandidis.
This may also help explain why humans form such large social groups. Some evolutionary biologists believe that we are able to build large social networks because gender differences in humans are more subtle than in other primates. For example, men and women are more similar in body size than male and female Neanderthals, says Tzompandidis. This is likely due to higher estrogen levels in the womb, he says.
Defining the factors that shaped the evolution of the human brain is more than just an intellectual pursuit: it can also shed light on diversity.
"Not all people are social or have incredible language skills - and that's okay. It doesn't make them less human," says Tzompandidis. Understanding how the brain developed can provide insight into whether certain cognitive traits are related to trade-offs, he says.
Music affects the rhythms of the human brain - research13.05.25, 07:12 • [views_3738]