This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: How did the human brain become so much larger than that of our closest evolutionary relatives? Part of the answer lies not in new genes, but in how humans and non-human apes use the genes they share.
Using brain organoids grown from stem cells, an international team led by Prof. Mareike Albert at TUD Dresden University of Technology compared early brain development in humans, chimpanzees, and gorillas. They found that in humans, genetic switches make certain genes more active, which likely make the cells that build the brain more branched—a trait linked to producing more neurons and, in turn, a bigger brain.
The study is published in the journal Nature Communications. In the brain, the neocortex is the area responsible for higher cognitive functions such as abstract thinking, long-term planning and speech. The human neocortex is much larger than that of other great apes.
Although certain human-specific genes have been linked to a larger brain, they alone do not explain the massive evolutionary expansion of the human neocortex. "Changes in brain size actually arise during development. This is when the majority of neurons are generated.
But developing brain tissue of nonhuman great apes is not available for research, and for good ethical reasons," explains Albert, research group leader at the Center for Regenerative Therapies Dresden (CRTD) and the Faculty of Biology of TUD Dresden University of Technology. "So we asked: How can we still compare brain development of different species side by side?" The answer was brain organoids, tiny, three-dimensional tissue structures grown from stem cells. Organoids resemble the developing brain, in this case the neocortex.
The researchers grew organoids from human, chimpanzee and gorilla stem cells and compared the early stages of brain development between the species. They found clear differences in how the three species use their shared genes. The human coding genome is 98%–99% identical to that of chimpanzees and gorillas.
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