He was the first (in 1864) to propose that the bones found in the German valley of Neanderthal in 1856 were not of Homo sapiens, but of a distinct species: Homo neanderthalensis.
He was among the earliest (in 1864) to identify the bones from the German valley of Neanderthal as belonging to a separate species, which he termed Homo neanderthalensis, differing from Homo sapiens.