Humans and chimpanzees may have split slowly, over millions of years
Somewhere in Africa lived the last ancestor we share with chimpanzees and bonobos. No fossil of it has ever been confirmed, and estimates of when our lines parted swing from thirteen to five million years ago. One reason may be that the split was not a clean break but a long, messy separation.
Classification itself had to be rethought. The tribe Hominini was first drawn to set humans apart from chimps and gorillas, on the assumption that humans were the odd ones out. Genetic evidence then showed Pan and Homo are closer to each other than either is to gorillas, so chimpanzees joined humans in Hominini while gorillas were moved to their own tribe. Anthropologist Richard Wrangham argued in 2001 that the common ancestor probably looked so much like a common chimpanzee that it deserved the name Pan prior.
Several fossils have been floated as candidates or near relatives. Sahelanthropus tchadensis, about 7 million years old, lived close to the divergence but may be just a Miocene ape that happens to resemble later hominins. Orrorin, around 6 million years old, has thigh-bone features shared with modern humans and australopithecines, and Ardipithecus, about 5.5 million years old, appeared perhaps while the lineages still interbred. Chimp fossils are scarce: the first, found in Kenya's Rift Valley, is only between 545 and 284 thousand years old. Researcher Mounier has proposed building a virtual fossil of the ancestor using statistical models of skull shape.
Molecular dates keep shifting. A 1998 estimate put the split at 10 to 13 million years ago; a 2016 study using especially clocklike mutations gave 9.3 to 6.5 million; and a 2025 analysis of complete telomere-to-telomere genomes from six apes narrowed it to 6.3 to 5.5 million. Yet a 2026 meta-analysis found estimates have drifted older over the decades and that genome-based figures compatible with the fossil record point to about 8 million years ago.
The deeper answer may be that different chromosomes separated at different times, perhaps over as long as 4 million years. Patterson and colleagues found the two emerging lineages still exchanging genes between 6.3 and 5.4 million years ago. Similar tangled speciation seems to have occurred between humans and gorillas, suggesting such untidy splits are normal among large primates.
Source: Chimpanzee–human last common ancestor
