Chimpanzee–human last common ancestor

The chimpanzee–human last common ancestor (CHLCA) is the last shared ancestor between humans and the species we call chimpanzees and bonobos. Scientists study this ancestor to learn more about how humans and these close relatives are connected.

Estimates suggest that humans and chimpanzees shared this common ancestor between five and thirteen million years ago. This time frame helps scientists understand how our species has changed over millions of years.

In studies of human genetics, the CHLCA serves as an important reference point. By comparing human DNA with chimpanzee DNA, scientists can calculate how quickly genetic changes occur in human populations.

Although researchers have searched for fossils of this ancestor, none have been found yet. Some ancient fossils, like Sahelanthropus tchadensis, Orrorin tugenensis, and Ardipithecus ramidus, might be related to the CHLCA, but scientists are still unsure because the fossils are incomplete.

Taxonomy

Main article: Hominini

The group called Hominini was made to separate humans (genus Homo) from chimpanzees (Pan) and gorillas (genus Gorilla). Scientists later learned that chimpanzees and humans are more closely related to each other than chimpanzees are to gorillas. Because of this, chimpanzees were grouped with humans in the Hominini tribe, and gorillas were placed in a separate group called Gorillini.

Some scientists suggested dividing Hominini into two smaller groups. They placed humans and other walking apes in a group called Hominina, and chimpanzees in another group called Panina.

All groups related to humans that came after the split from chimpanzees belong to the subtribe Hominina, including humans (Homo) and Australopithecus. These groups are known as "hominins".

Fossil evidence

Scientists have not found fossils that clearly show the last common ancestor of humans and chimpanzees. Some ancient fossils, like Sahelanthropus tchadensis and Orrorin, lived around the time humans and chimpanzees separated from each other, about 7 million years ago. These fossils have some features that are similar to both humans and chimpanzees, but it is hard to know if they are direct ancestors or just close relatives.

Another fossil, Ardipithecus, appeared after the split, around 5.5 million years ago. It shares some traits with chimpanzees but is not complete enough to know its exact place in our family tree. Because fossils from this time are rare, scientists are using computers to learn more about our shared ancestors.

Age estimates

Scientists have tried to find out when humans and chimpanzees last shared a common ancestor. In 1998, they thought it might have been between 10 and 13 million years ago. By 2009, some scientists suggested it was between 7 and 10 million years ago.

More recent studies, like one from 2022, suggest it might have been between 6.6 and 4.7 million years ago. A 2025 study, using full genome sequences, estimated the split happened between 6.3 and 5.5 million years ago.

Gene flow

It is hard to know exactly when chimpanzees and humans last had a common ancestor. Their DNA did not all separate at once. Instead, different parts of their DNA split over millions of years. During this time, the two groups mixed their genes as recently as between 6.3 million and 5.4 million years ago.

Scientists think the split between chimpanzees and humans happened in the last 9 million years. After the first split, there were times when the groups mixed their genes again before separating. The final split happened sometime between 13 million and 4 million years ago, but scientists are not sure of the exact time. This mixing makes it difficult to pick one date for when humans and chimpanzees last shared a common ancestor.