The evolution of modern day humans has always been a topic that has been shrouded in mystery. Some of what is known is that Neanderthals, an archaic human species that lived on this planet up until about 11,700 years ago, interbred with our species (Homo sapiens) at some point in time. Although their brains were about as big as ours, anthropologists think they must have worked differently due to the fact that they never achieved the sophisticated technology and artistry modern humans have.

Since brains do not fossilize, it has been challenging to see how these two early human species have changed over time. To help answer this question, Dr. Alysson Muotri and his team at UC San Diego created so-called “mini-brains” using stem cells and gene editing technology to better understand how the Neanderthal brain might have functioned.

For this study, Dr. Muotri and his team closely evaluated the differences in genes between modern day humans and Neanderthals. They found a total of 61 different genes, but for this study focused on one in particular that plays a role in influencing early brain development.

Using gene editing technology, the team introduced the Neanderthal version of the gene into human stem cells. These stem cells, which have the ability to become various cell types, were then used to create brain cells. These cells eventually formed brain organoids or “mini-brains”, 3D models made of cells that can be used to analyze certain features of the human brain. Although they are far from perfect replicas, they can be used to study physical structure and other characteristics. In a previous CIRM funded study, Dr. Muotri had used “mini-brains” to model an autism spectrum disorder and help test treatments.

Dr. Muotri and his team found that the Neanderthal-like brain organoids looked very different than modern human brain organoids, having a distinctly different shape. Upon further analysis, the team found that modern and Neanderthal-like brain organoids also differed in the way their cells grow. Additionally, the way in which connections between neurons formed as well as the proteins involved in forming these connections differed between the two organoids. Finally, electrical impulses displayed higher activity at earlier stages, but didn’t synchronize in networks in Neanderthal-like brain organoids.

According to Muotri, the neural network changes in Neanderthal-like brain organoids mimic the way newborn primates acquire new abilities more rapidly than human newborns.

In a news release from UCSD, Dr. Muotri discusses the next steps in advancing this research.

“This study focused on only one gene that differed between modern humans and our extinct relatives. Next we want to take a look at the other 60 genes, and what happens when each, or a combination of two or more, are altered. We’re looking forward to this new combination of stem cell biology, neuroscience and paleogenomics.”

The full results of this study were published in Science.