Before the early 2010s, scientists were conflicted on the question of Homo sapiens interbreeding with Neanderthals, but since then, multiple studies have shown the incredible overlap between Neanderthal and human DNA - enough that approximately 1%-4% of modern human DNA traces directly back to Neanderthal ancestry.
Neanderthals coexisted with modern humans for tens of thousands of years, and the two groups certainly met. Evidence shows that Homo sapiens not only procreated with Neanderthals - they also slew and ate them.
It's not surprising that prehistoric humans mated with Neanderthals since prehistoric people were notoriously promiscuous. But while science proves humans mated with Neanderthals, the evidence still leaves some questions open. When did they begin to interbreed? Was it consensual? And were there human-Neanderthal relationships?
Only One Group Of Humans Doesn't Have Neanderthal DNA
Homo sapiens migrated around the world, sometimes mingling with other hominid species. But just one group of modern humans shows no evidence of interbreeding with Neanderthals.
Modern ethnic groups from around the world carry Neanderthal DNA from interbreeding - except for people with solely African ancestry. Subsaharan Africans never interacted with Neanderthals, and thus didn't have a chance to mingle their DNA. Everyone else carries around 1-4% Neanderthal genes.
Humans Share 99.7% Of Their DNA With Neanderthals
Homo sapiens and Neanderthals most likely mated and fought each other, but the two groups might have been nearly indistinguishable when they coexisted in Europe and the Middle East.
That's because Neanderthal DNA is almost identical to human DNA. Humans and Neanderthals shared 99.7% of their DNA. That makes Neanderthals much closer genetic relatives than chimps, who share 98.8% of their DNA with humans.
In addition to the close genetic relationship, Homo sapiens and Neanderthals crossbred, introducing additional Neanderthal DNA into the human genetic pool.
Neanderthals May Have Gone Extinct Due To Hybridization
Interbreeding with Homo sapiens might have been a bad idea for Neanderthals. The Neanderthal Y chromosome was not completely compatible with the human Y chromosome. As a result, if a Neanderthal male procreated with a human female, the pregnancy would have frequently ended in a miscarriage.
Population geneticist Fernando Mendez identified the mutations on the Neanderthal Y chromosome that would trigger an immune response from a human woman. If she became pregnant, the woman's immune system could have caused a miscarriage.
In fact, the Neanderthals may have gone extinct after intermixing with Homo sapiens and essentially becoming absorbed into their group.
Homo Sapiens Slew And Ate Neanderthals
Home sapiens and Neanderthals might have fought each other for 100,000 years as Homo sapiens tried to expand from Africa into Neanderthal territory in Europe and Asia. In November 2020, evolutionary biologist and paleontologist Nicholas R. Longrich said that although it's tempting to think the two groups might have got along, "biology and paleontology paint a darker picture. Far from peaceful, Neanderthals were likely skilled fighters and dangerous warriors."
Archaeological evidence indicates that Neanderthals used spears to hunt big game, so they likely also used such tools to protect themselves, and both Neanderthal and Homo sapien prehistoric remains show signs of skull and upper-body trauma.
Shanidar 3, for example, a 40-year-old Neanderthal who lived in Iraq around 50,000 years ago, was slain after a spear pierced him through the rib cage. Anthropologist Steven Churchill demonstrated that the tool that took Shanidar 3's life could have been a lightweight projectile spear. A Neanderthal jawbone discovered from a cave in southwestern France showed signs of cut marks from a stone tool, indicating the Neanderthal child was slain and eaten.
Longrich said Neanderthals likely survived for 100,000 years despite the conquest because they were far more familiar with the terrain, and had muscular bodies and large eyes that aided in close combat and dark lighting conditions. It's not clear why Homo sapiens eventually prevailed; perhaps they developed better weaponry or hunting techniques.