Biologists call these strange creations human brain organoids. It depicted a clump of human brain cells, silhouetted in black against the milky white of a petri dish. If you put loose brain cells together, they will multiply and interlink until they’ve cohered into autonomous globs of tissue. Human brain organoids practically make themselves. He and his colleagues have revived genetic material from the hominin fossil record to create “Neanderthalized” brain organoids.