FOXP2 gene is required for language and speech development and is present in all animals. It is a transcription factor which encodes for a regulatory protein. Both modern humans and Neanderthals share FOXP2 gene which differs from chimpanzee version by two amino acids. Its the different regulation of the same gene which made modern humans more capable of using language and speech. Neanderthals did use language rudiments but not completely constructed languages. There might be other speech genes involved too which differed between modern day humans and Neanderthals but not FOXP2.
