The placenta that feeds the fetus also regulates the contribution of essential hormones for the development of the brain: it may have given man an extra gear.
The secret of the brain so much more evolved of humans could reside in the placenta, the temporary organ responsible for metabolic exchanges between the maternal and fetal organism. According to a new hypothesis proposed by researchers from the universities of Cambridge and Oxford, the placenta, which also has the task of producing and regulating pregnancy hormones, could having played a very important role in the evolution of the human brainand have contributed to the behavioral traits that make man a social being. The idea is explained in an article published in the scientific journal Evolutionary Anthropology.
Hormones and brain
“Small variations in prenatal levels of steroid hormones, such as testosterone and estrogen, can predict the social and cognitive learning rate in babies and even the probability of pathologies such as autism. This prompted us to consider their relevance for human evolution “, explains Alex Tsompanidis, senior researcher of the Autism Research Center of the University of Cambridge and the main author of the study.
Tsompanidis and colleagues have tried to search for the physiological mechanisms that may have contributed to making our species so predisposed to living in large and complex groups, a context associated with the development of larger and more efficient brains. One of these mechanisms could see prenatal steroid hormones as protagonists such as Testosterone and estrogenthe chemical messengers to whom the fetus is exposed in pregnancy, which can affect both the development of the brain and on human social behavior.
The placenta: an organ for hormonal exchanges
Previous studies on human brain organoids have allowed for the first time to clarify the effects of these hormones on brain development: testosterone, the main male hormone, can increase the size of the brain, while estrogen, the main female hormones, improve connectivity between neurons.
And the placenta? AND The meeting point between these hormones and the unborn childbecause it connects the endocrine systems of mom and child. In fact, this organ produces hormones throughout pregnancy, as well as providing nutrients and antibodies to the fetus and to regulate the exchange of oxygen and carbon dioxide.
The advantages provided by the human placenta
Not negligible is also the fact that the placenta regulates the duration of pregnancythrough hormonal production and the synchronization of fundamental physiological processes for mother and child. But then, How the human placenta benefits usgiving us – based on the hypothesis of British scientists – a bigger brain?
Based on the new study, it would do so favoring the production of estrogen on that of testosteroneusing an enzyme called aromatase which is present in greater quantities in the human placenta, compared to that of other primates.
This enzyme transforms testosterone into estrogenmore prevalent hormones in human pregnancies than those of species close to us, and which have important functions in regulating the sexual differentiation.
In order for man to form complex social groups, the maintenance of high fertility in females and the reduction of potential conflicts for partners and resources in males were important.
High testosterone levels compared to estrogen before birth lead the scale needle to hang more in the male direction both for the anatomical characteristics (strength, physical dimensions), and for behavioral ones (competition). But in human beings these differences are attenuated compared to other primates and compared to extinct species such as Neanderthals. While characteristics dictated by estrogen seem to prevail (such as reduction of hair).
A transitional but relevant organ for our species
All these pieces of the puzzle contribute to forming the hypothesis that The placenta may have made the largest and most interconnected human brainsfinely regulating the exposure of the brain of the hidden to steroid hormones and making the contribution of estrogen prevail over that of testosterone. This balance may have brought to a reduction of conflicts between malesimproved women’s fertility sapiens and contributed to the formation of larger social groupscohesive and complex. Who have fed and further increase our brain.
