New Innovation
Scientists have added a small piece of human DNA to mice, and something surprising happened—their brains grew larger than normal. This discovery could help us understand how human intelligence developed over time.
The mice with human DNA had brains that were about 6.5% bigger than usual. This change happened because the human DNA helped make more brain cells and made the outer part of the brain larger. These results give scientists new clues about why human brains are so much bigger than those of other animals, like chimpanzees.
Why Human Brains Are So Big
Compared to chimpanzees, human brains are three times larger. Scientists believe this change happened quickly in evolution, but they weren’t sure exactly how.
One possible reason could be special parts of our DNA called Human Accelerated Regions (HARs). These are pieces of DNA that changed a lot after humans split from chimpanzees. One of these pieces, called HARE5, seemed to be important for brain growth.
What Scientists Did
Researchers took HARE5 from human DNA and replaced the same part in mouse DNA. As the mice grew, the ones with the human HARE5 developed larger brains. A special type of brain cell, called radial glia, grew much faster in these mice. These cells are important because they help create other brain cells.
Scientists also found four small changes in human HARE5 that made it different from the chimpanzee version. These changes helped the brain cells grow more.
However, it’s still not clear if the mice with bigger brains are smarter or have better memory.
Growing Mini Brains in the Lab
To study this more, scientists made tiny brain models (called organoids) in the lab. When they used chimpanzee HARE5, fewer brain cells grew. But when they used human HARE5, the models made more and better-developed brain cells.
They also found that HARE5 affects a signaling pathway that helps stem cells grow—this may be one reason our brains are so complex.
The next step is to study how HARE5 works with the other 3,000 HARs in our DNA to fully understand how the human brain became what it is today.
“There are many, many different things that make the human brain so special,” said scientist Debra Silver.
