What makes us human?
That’s a loaded question, I’ll admit. It also needs some kind of context: what makes us human and not something else. For instance, what makes us human and not dolphins? Listing differences between humans is one of the easier answers to this question. A harder one has been addressed by researchers from the University of California San Diego: what makes us human, and not Neanderthal or Denisovan? Specifically, what makes our brains human brains and not Neanderthal or Denisovan brains? Neanderthals and Denisovans are now-extinct close relatives of our own species, Homo Sapiens, and lived from 2.5 million to 12 thousand years ago (roughly).
The researchers found 61 genes that were distinct between modern human beings and our Neanderthal and Denisovan relatives. But which one of these made the much-feted change in brain anatomy which is believed to have led to our globalising success? One of the 61 genes found was already noted to be involved in brain processes (a gene called NOVA1), so the researchers began there. It was found that a single tiny mutation was the only difference between modern human NOVA1 genes and those of Neanderthals, so human stem cells were gene edited to carry a Neanderthal NOVA1 gene and were then used to generate brain cells. This resulted in a brain ‘organoid’ in the lab which was ‘Neanderthalised’.
So, how different were these Neanderthal organ(oid)s to those of the modern humans? Incredibly different, as it turns out. The shapes of the organoid itself was notably different to a casual observer. The cells grew differently, and the synapses were different as well (synapses are the connections between brain cells, and how they communicate with each other). And remember, this is just one small change in one gene.
Is this genetic change the only one that separates our much-celebrated brain from that of the extinct Neanderthal? We don’t know, but it seems unlikely. The team behind this study is looking forward to repeating this study using some of the other differences out of the 61 identified, and even seeing what happens when two or more of the genes are changed at once. This is the beginning of an exciting line of research which seems likely to enhance our understanding of what makes our brains what they are, and why they seem to be capable of things not seen elsewhere in the animal kingdom.
I hope you learnt something new!
Read more:
https://science.sciencemag.org/content/371/6530/eaax2537 - original article in Science
https://www.youtube.com/watch?v=5FBxnkzI9HUv – Scientist from the team talking about the research (22min)
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