Sesame seed-size brains created from a mix of human and Neanderthal genes lived briefly in petri dishes in a University of California, San Diego laboratory, offering tantalizing clues as to how the organs have evolved over millennia.
Scientists have long wondered how human beings evolved to have such big, complex brains. One way to figure that out is by comparing modern genes involved in brain development with those found in our ancient cousins. Though scientists have found plenty of fossilized remains from Neanderthals — cousins of modern humans that died out about 37,000 years ago — they have yet to find a preserved Neanderthal brain. To bridge that gap in knowledge, a research team grew tiny, unconscious "minibrains" in petri dishes. Some of the brains were grown using standard human genes, and others were altered using the gene-editing tool CRISPR to have a brain development gene taken from Neanderthal remains.
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It's not the first time tiny brains have been grown for research, as Live Science has reported, but it is the first time anyone has cultivated a hybrid of the human organ with an ancient human cousin.
Specifically, the researchers replaced the human NOVA1 gene in some of the stem cells used to grow the minibrains with a NOVA1 gene pieced together from genetic remnants in the bones of long-dead Neanderthals. NOVA1, researchers know, plays a role in brain development.
The difference between the completely human brain and the human-Neanderthal hybrid was immediately obvious, Alysson Muotri, a neuroscientist at UCSD who led the project, told Nature (opens in new tab).
Human minibrains tend to be smooth spheres, like little marbles. The Neanderthal brains were smaller and more irregular, the researchers reported. They also took longer to develop. Anyone looking at the different petri dishes could immediately spot the difference, the researchers said.
A closer analysis revealed that the part-Neanderthal minibrains were more chaotic in their neural activity and produced different sets of proteins than the all-human ones
Moutri and her team chose NOVA1 for their experiment because it plays a role in forming the connections between nerves, and because damage to this gene can lead to neurological disorders — making it a key target of study for researchers hoping to understand the brain.
Neanderthal NOVA1 genes are also relatively easy to synthesize. Only one letter in their genetic code is different from the human variant.
NPR reported that the differences suggest Neanderthal brains matured more quickly than human brains did, making Neanderthals more capable at younger ages. But that quick development robbed Neanderthals of the extended development period that likely gave human children advantages in complex thought and social bonding.
The paper was published Feb. 12 in the journal Science.
Originally published on Live Science.