About 100,000 years ago, a diverse group of hominids, or humanlike species, occupied Earth. By 30,000 years ago, however, only Homo sapiens—the most modern species—remained. One of the most hotly debated issues in paleoanthropology, the study of human origins, focuses on how Homo sapiens evolved to outlive the other hominids.

The current best explanation for the beginning of modern humans is the Out of Africa model. This holds that Homo sapiens arose in Africa and gradually replaced hominid species in the other parts of the world to which they migrated. To address the question of why our species survived, paleoanthropologists make certain assumptions about lifestyle and behavior based on fossil evidence.

The fossil record shows that early Homo sapiens—who had a body plan more or less like our own—and Neanderthals (Homo neanderthalensis)—a separate species characterized by a large, low-sloping cranial vault and a short, robust skeleton—inhabited the same land at about the same time, between approximately 30,000 and 40,000 years ago. Both species developed hunting tools and used fire. But paleoanthropologists theorize that Homo sapien understanding of geography might have given them a decisive competitive advantage. Artifacts suggest that nearly all known early Homo sapien settlements were situated on hilltops and high ridges. Their ability to survey large areas of land from such vantage points would very likely have helped their hunting strategy. Neanderthals, on the other hand, lived in valleys that did not permit a clear view to the horizon.

Even though the Neanderthals may have arrived first on the scene, the more modern species, Homo sapiens, came out ahead in the competition for resources. Over a period of roughly 5,000 to perhaps 10,000 years, the Neanderthals were gradually displaced to remote areas like the British Isles, northern Germany, and southern Spain. About 30,000 years ago, they became extinct.

While fossil evidence suggest that the Neanderthals may have adopted some of the technologies that made modern humans more effective hunters, recent DNA evidence suggests that Neanderthals and Homo sapiens did not interbreed. Because Neanderthals did not contribute mitochondrial DNA to modern humans, they are most likely not our direct ancestors. This finding provides further support to the Out of Africa model.

Look for trends in height data of North American boys from 1880 and 1960 in this NOVA classroom activity.

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