German biologists have found out, that the size of the neocortex in different species is directly influenced by the duration of pregnancy.
The neocortex, or new cortex, the youngest and largest part of our brain responsible for speech and the process of thinking, has significantly increased in size during human evolution. In an effort to understand the reasons for this increase, scientists at the Max Planck Society’s Institute for Molecular Cell Biology and Genetics have focused their previous research on a gene called ARHGAP11B, which is found only in humans and causes increased production of brain stem cells.
Now, however, the same research group in a study of mice has discovered a completely different cause of the enlargement of the neocortex. As it turned out, the longer the duration of pregnancy in a certain species, the longer the neurogenic phase – the period of time in which the formation of neocortex nerve cells occurs, and the greater the number of these cells are in its upper neuronal layers, which, in fact, is an indicator of an increase in the new cortex …
“We found that mouse embryos with a longer gestation period (20.5 days) did indeed have a longer neurogenic phase and produced significantly more neocortex nerve cells than mouse embryos with a shorter gestation period (19.5 days),” says one from study authors Samir Waid. According to scientists, humans have the longest pregnancy among primates, the longest neurogenic phase and the most nerve cells in the neocortex. Specifically, the human neurogenic phase is eight days longer than that of the gorilla or orangutan. “During the neurogenesis of the neocortex, the nerve cells in the upper layer are the last to form,” explains Samir Waid. “Therefore, lengthening this last phase of neurogenesis leads to a specific increase in nerve cells in the upper layers of the neocortex, which is a sign of its evolutionary expansion.”
In addition, the authors of the study found that the mother’s womb also affects the duration of neurogenesis. They placed the embryos of mice with a short gestation period in the womb of mothers in which the pregnancy lasted longer, and vice versa, and as a result, they found that the time of formation of nerve cells in these cases changes.
According to Wieland Huttner, who led the research team, the results of the study identified a second factor besides the ARHGAP11B gene that increases brain size during evolution – and that factor is time.
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