Here’s the deal: you can write or say Neanderthal or Neandertal, but you should only write Homo neanderthalensis and say “Homo neander-TAL-ensis.” I promise that will make sense by the end of this.
The name comes from Neander Valley, Germany, where the first recognized Neanderthal fossil was found in 1856 (other Neanderthal bones had been discovered earlier, but people didn’t know what to make of them).