Previous studies had shown that a particular gene, when expressed in mice and ferrets at non-physiologically high levels, led to an expansion of the neocortex, but its relevance to primate evolution has never been clear.
The human neocortex, the evolutionarily youngest part of the cerebral cortex, is about three times larger in us than that of our closest relatives, the chimpanzees, and its wrinkle fold increased during evolution to accommodate the restricted space of the skull.
How did our neocortex get so big?
Now, a team of scientists has developed larger-than-usual monkey brains by giving marmoset fetuses a gene that is unique to humans. This may sound more like the Planet of the Apes sci-fi movie saga, but the research could shed light on how this all-important gene helped make us human.
Researchers at the Max Planck Institute for Molecular Cell Biology and Genetics in collaboration with the Central Institute for Experimental Animals, expressed a specific gene: ARHGAP11B that is only found in humans and activates brain stem cells to form more stem cells – a prerequisite for a bigger brain. This gene was introduced into 101-day fetuses (50 days before birth) of common marmosets and they found that it produced an enlarged neocortex, a part of the cerebral cortex that is exceptionally larger in humans compared to other primates and is responsible for abilities. advanced cognitive skills, such as reasoning and language.
Influence on human evolution
This study is not only incredible, it is also enlightening. It could replicate the time in evolution where humans split from other primates . All due to a single gene.
“In fact, we found that the neocortex of the brain of the common marmoset was enlarged and the surface of the brain bent. His cortical plate was also thicker than normal, “said Michael Heide, lead author of the study, in the journal Science that publishes the study.” In addition, we were able to see a greater number of basal progenitors of the radial glia in the subventricular zone. external and a greater number of neurons of the upper layer. This type of cortical neuron increases in the evolution of the primates “.
Given the importance of the size of the neocortex in the development of human cognitive abilities, it is clear that ARHGAP11B is a specific human gene that was produced in our lineage after the divergence of chimpanzees but before our separation from Neanderthals and Neanderthals. Denisovans, which means that these extinct relatives also had the “big brain gene.”
The gene had previously been expressed in mice and ferrets, but this is the first time that it has been shown to have the same brain-enlarging effect in a non-human primate.
What happened to the fetuses?
The researchers have clarified that the marmoset fetuses used in the experiment were treated with high ethical standards and were not carried to term. According to the authors, letting them be born would have been irresponsible for not knowing what type of behavior they were going to present.
Referencia: Michael Heide, Christiane Haffner, Ayako Murayama, Yoko Kurotaki, Haruka Shinohara, Hideyuki Okano, Erika Sasaki and Wieland B. Huttner. Human-specific ARHGAP11B increases size and folding of primate neocortex in the fetal marmoset,. Science, 2020 DOI: 10.1126/science.abb2401
