Neanderthals were primitive, brutish, and less intelligent than modern humans.

In 1908, workers excavating a limestone quarry near La Chapelle-aux-Saints in southern France uncovered the skeleton of an elderly Neanderthal man. The bones reached Marcellin Boule at the Muséum National d'Histoire Naturelle in Paris, who spent three years producing the definitive scientific portrait of Neanderthal anatomy. His 1911 monograph described a creature with a stooped posture, bent knees, and a head thrust forward on a thick neck, the prototype of the brutish cave dweller. Boule concluded that Neanderthals had been physically and mentally inferior to early modern humans, capable of little more than grunting and crude tool use. The image spread rapidly: textbooks, museum dioramas, and newspaper illustrations depicted them as shambling subhumans swept aside by the superior intelligence of Homo sapiens.

What Boule had actually examined was a man crippled by severe arthritis. A reanalysis of the La Chapelle skeleton in the 1950s by William Straus and A.J.E. Cave revealed that the stooped posture and bent joints were symptoms of degenerative disease, not species-typical anatomy. When reconstructed without the distortions of arthritis, Neanderthals stood upright and moved much as modern humans do. The image of the hunched brute had been built on a misdiagnosis.

Archaeologists excavating Neanderthal sites across Europe and the Middle East then accumulated evidence of sophisticated behavior the brutish model could not accommodate. Ralph Solecki's 1960 excavation at Shanidar Cave in Iraqi Kurdistan uncovered a Neanderthal burial with pollen clusters around the remains, which he interpreted as evidence of mourners placing flowers on the body. The Mousterian tool industry, long dismissed as crude, involved careful raw material selection, heat treatment of flint, and production of standardized tools requiring significant planning. Neanderthals also used pigments, ochre and manganese dioxide, in ways consistent with symbolic behavior once considered the exclusive domain of anatomically modern humans.

The most consequential revision came from genetics. In 2010, Svante Pääbo and colleagues at the Max Planck Institute for Evolutionary Anthropology published the first draft sequence of the Neanderthal genome, reconstructed from bone fragments at Vindija Cave in Croatia. The analysis revealed that people of non-African ancestry carry approximately one to four percent Neanderthal DNA, the genetic signature of interbreeding between Neanderthals and modern humans who spread out of Africa roughly 60,000 to 70,000 years ago. Some of those inherited sequences affect immune responses, skin pigmentation, and susceptibility to specific diseases, meaning Neanderthal DNA has shaped modern human biology in measurable ways.

Boule's portrait was a projection as much as a description. The La Chapelle man had survived into old age with severe arthritis, a condition requiring sustained care from others. Had Boule read that evidence clearly, it might have suggested something about Neanderthal society from the beginning. Instead it took a century of reanalysis, fieldwork, and ancient DNA to replace the stooped brute with something closer to the truth: a species sophisticated enough to leave its mark permanently on the human genome.

The interbreeding evidence also complicated the longstanding model of human evolution as a simple branching tree in which modern humans replaced Neanderthals through competitive superiority. The genetic data indicated instead a more complex picture of overlapping populations, periodic gene flow, and a degree of biological continuity between archaic and modern human lineages that the replacement model had ruled out. The discovery shifted the question from why Neanderthals went extinct to how completely they did, and whether extinction is even the right frame for a population that left heritable traces in the majority of humans alive today.