Neanderthals are the human species known to have contributed DNA to modern non-African populations.
Genomic studies show that most people with ancestry outside Africa carry roughly 1–4% Neanderthal-derived DNA, although newer estimates often place the average closer to 1.5–2.6%. The main interbreeding episode probably occurred about 47,000–65,000 years ago, after some Homo sapiens populations left Africa and encountered Neanderthals in Eurasia.
Neanderthals were not direct ancestors of modern humans in a simple straight line. They were a closely related sister group that lived across Europe and parts of western and central Asia until roughly 40,000 years ago. Their surviving genetic contribution is uneven: some inherited variants affect immunity, skin biology, metabolism, and other traits, while much Neanderthal DNA was likely removed by natural selection.
A common mix-up is Denisovans, another archaic human group that contributed DNA especially to populations in Melanesia and parts of Asia. Neanderthals and Denisovans were related to each other, but they are distinct groups.