Israeli historian Yuval Noah Harari writes in his international bestseller Sapiens: A Brief History of Humankind,

Tolerance is not a Sapiens trademark. In modern times, a small difference in skin color, dialect or religion has been enough to prompt one group of Sapiens to set about exterminating another group. Would ancient Sapiens have been more tolerant towards an entirely different human species? It may well be that when Sapiens encountered Neanderthals, the result was the first and most significant ethnic-cleansing campaign in history.