Scientists Discover Why Our Brains Are So Big

  • Kelly Shen ’23

A defining characteristic of mammals, and especially humans, are our very large brains. In fact, the human brain typically reaches about 1,500 cm3, nearly three times the size of the gorilla brain (500cm3) or the chimp brain (400cm3). How did we develop larger brains than most other organisms? Scientists believe they have finally unlocked some clues, starting with cells from our primate cousins. 

The Medical Research Council (MRC) Laboratory of Molecular Biology in Cambridge, UK, has grown brain “organoids” out of stem cells called neural progenitors. These cells are shaped like cylinders, and when they split make daughter cells of the same shape. Previous research in mice shows that this process of multiplication takes only a few hours. In chimps and gorillas it takes five hours, and in human seven. The extra time enables humans to develop more brain cells. In addition, the lab showed that the human brain organoids grew a lot bigger than the chimp and gorilla organoids, further supporting the scientists’ findings. 

The scientists also studied the gene behind the difference in development times, such as what genes are turned on and off in our brains vs. the chimp and gorillas’ brains. A difference was found in the gene ‘ZEB2’. It was turned on faster in gorilla brain organoids than in the human organoids. Interestingly enough, turning on this gene earlier in human brain organoids led them to develop in a more gorilla-like way, while turning the gene on later in gorilla brain organoids led them to develop inna more human-like way.

Image attribution:

“Human Brain” by InjuryMap is is licensed under the Creative Commons Attribution 4.0 International license.

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