Neanderthals were modern humans' closest relatives, and the two types of humans lived in many of the same habitats and interbred multiple times before our cousins died out around 40,000 years ago, which is why some Neanderthal DNA still lives in most Eurasians today.
Yet despite this closeness, Neanderthals' (Homo neanderthalensis) and Homo sapiens' lineages diverged sometime between 400,000 and 800,000 years ago, and the two species differed in many ways.
