Ancient teeth reveal that human evolution was a tangled tree, not a straight line

Science · Published 12 October 2026 Swipe more like this →

In short: For decades, we imagined human evolution as a steady, linear march from apes to modern humans. However, new fossil discoveries in Ethiopia are shattering that image, revealing a complex, branching history where different human ancestors lived side-by-side in the same landscape.

At the Ledi-Geraru site in Ethiopia, researchers have uncovered evidence that challenges the traditional view of human ancestry. Rather than a direct progression, the fossil record suggests a 'tangled, branching tree' where multiple species coexisted. Among the finds are 13 teeth that include both members of the genus Homo and a previously unknown species of the genus Australopithecus.

This discovery is significant because it places these distinct lineages in the same location between 2.6 and 2.8 million years ago. This coexistence contradicts the old perception of a linear evolution. Instead, it suggests that as the climate in East Africa became drier, nature 'experimented' with different ways of being human, with various species branching out into different ecological niches.

The findings highlight how much of the evolutionary story remains incomplete. While scientists have identified the mandible and teeth of the earliest Homo specimens, dating back to 2.8 million years ago, the broader picture of how these lineages interacted is still emerging. These discoveries, including the ability to extract molecular information from 1.7 million-year-old teeth using new methods, are fundamentally reshaping our understanding of the human lineage.

This pattern of branching is not unique to humans; it is a characteristic shared by every other tree of life. The presence of these diverse species in the same African sediments confirms the antiquity of our lineage and underscores the complexity of the evolutionary experiments that occurred millions of years ago.

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