(CNN)Brains are not preserved in the fossil record, making it impossible to know how modern human brains differ from our long-extinct ancestors, the Neanderthals.
From fossilized skulls we know that their brains were big -- slightly bigger than ours, in fact -- but they tell us little about their neurology and development.
Scientists from the University of California San Diego have come up with an exciting and provocative way to begin to answer this question. They have created blobs of brain tissue genetically modified to carry a gene that belonged to Neanderthals and other archaic hominins but not Homo sapiens.
While the research is at a very early stage, the researchers found that the Neanderthalized brain organoids produced significant changes in how the brain is organized and wired.
"The question here is what makes us human," said Alysson Muotri, professor and director of the Stem Cell Program at the University of California San Diego School of Medicine's Institute for Genomic Medicine.
"Why are our brains so different from other species including our own extinct relatives?"
Muotri, who has so far spent eight years on the project, calls his work "neuroarchaeology."
"When you find a piece of bone or (charcoal) and you try to reconstruct how that society lived, what they were doing, how they connected with each other -- you try to understand the mind. We are doing the