Philip Ball’s “mini brain,” stained with fluorescent dye to show the neurons. Photo: Chris Lovejoy and Selina Wray, UCL

Plans to grown Neanderthal “mini-brains” take this already science-fictional biomedical technology to new extremes. Mini-brains are a form of organoids—tiny organ-like clusters of cells grown in the laboratory, both for fundamental research in biology and also for possible transplantation to replace damaged or malfunctioning organs. But the new proposal, by eminent palaeontologist Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, would use the technique to investigate our extinct close relatives the Neanderthals, attempting to figure out what if anything made their brains different from those of the early Homo sapiens with whom they coexisted.

It’s a bold idea, and indeed some researchers see it as a long shot that might tell us rather little. But at the very least it shows how advances in genetics, tissue engineering and stem-cell technology, and palaeontology could converge to let us address questions one might have imagined long lost in the mists of time.

Mini-brains are formed when stem cells—either made by “induced” means from adult body cells or taken from human embryos—are coaxed into becoming neurons, the nerve cells that signal to each other in the brain. These stem cells are capable of growing into any tissue in the body, and in a cell culture (where they are sustained in a medium that supplies essential nutrients) they can be guided into particular tissue types—heart, kidney or muscle cells, say—typically by adding the right cocktail of proteins to the medium.

But in general, these cultured stem cells don’t just proliferate into a vague mass of the target cell type. Instead they develop some of the organisation found in real organs—an indication that cells are already programmed with the instructions needed for building the complex structures and organs of the body. So it is for neurons grown from cultured stem cells: they develop into brain-like structures, for example making layers of neurons like those seen in the cortex. The resulting brain organoids can grow to the size of a small pea before cells in the interior start to die for lack of a blood supply. The organoid is far from a miniature version of a real brain, but it reproduces enough of the developing brain’s structure to provide researchers with…

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